{
  "data": {
    "a": {
      "slug": "langsmith",
      "name": "LangSmith API + MCP",
      "vendor": "LangChain",
      "vendorUrl": "https://www.langchain.com/langsmith",
      "kind": "http-api",
      "category": "agent-observability",
      "summary": "LangChain's hosted tracing, evaluation, prompt hub and dataset platform, framework-agnostic with Python and TypeScript SDKs and OpenTelemetry ingest.",
      "url": "https://www.anchorterminal.com/tools/langsmith",
      "markdownUrl": "https://www.anchorterminal.com/tools/langsmith.md",
      "slimMarkdownUrl": "https://www.anchorterminal.com/tools/langsmith.min.md",
      "jsonUrl": "https://www.anchorterminal.com/api/v1/tools/langsmith.json",
      "repo": "https://github.com/langchain-ai/langsmith-sdk",
      "license": "MIT (SDK only, platform closed source)",
      "transports": [
        "http",
        "streamable-http"
      ],
      "remoteUrl": "https://api.smith.langchain.com",
      "packages": [
        {
          "registry": "pypi",
          "name": "langsmith"
        },
        {
          "registry": "npm",
          "name": "langsmith"
        }
      ],
      "auth": "mixed",
      "authNotes": "API key in the `X-Api-Key` header (personal or service keys, workspace-scoped). The remote MCP server uses OAuth 2.1 with dynamic client registration for interactive clients, or the same API key header for headless ones.",
      "pricing": "freemium",
      "pricingNotes": "Developer is free for 1 seat with 5,000 base traces a month. Plus $39 a seat a month with 10,000 base traces, unlimited seats and one free small deployment. Enterprise custom. Beyond the included traces, a base trace costs 0.005 LSU ($5 per 1,000 at $1 an LSU) with 14-day retention, and upgrading to an extended trace with 180-day retention adds 0.0025 LSU. Compute for deployments, sandboxes and tuned evaluators is billed in LCUs at $1.50 each. Self-hosting and BYOC are Enterprise only (https://www.langchain.com/pricing).",
      "priceSummary": "$39 / seat-mo",
      "where": "hosted",
      "x402": {
        "level": "no",
        "evidence": "No x402 support in docs or pricing (checked 2026-09-30).",
        "endpoints": []
      },
      "toolCount": null,
      "popularity": {
        "githubStars": 1064,
        "npmWeekly": 7588622,
        "pypiWeekly": 17835288,
        "asOf": "2026-09-30"
      },
      "docsUrl": "https://docs.langchain.com/langsmith/observability",
      "llmsTxt": "https://docs.langchain.com/llms.txt",
      "openapi": "https://api.smith.langchain.com/openapi.json",
      "capabilities": [
        "obs.traces",
        "obs.evals",
        "obs.prompts",
        "obs.datasets",
        "obs.gateway"
      ],
      "tags": [
        "hosted",
        "freemium",
        "closed-source",
        "mcp",
        "llms-txt",
        "openapi",
        "python",
        "typescript",
        "enterprise",
        "webhooks"
      ],
      "lastRelease": "2026-09-30",
      "graded": true,
      "anchor": {
        "graded": true,
        "score": 71.1,
        "grade": "BB",
        "agentReady": true,
        "rank": 119,
        "ranked": true,
        "rankOf": 722,
        "categoryRank": 3,
        "methodology": "0.4",
        "run": "2026-10-01",
        "scores": {
          "ergonomics": 76,
          "maintenance": 85,
          "payments": 40,
          "reliability": 81,
          "schema": 86,
          "security": 77,
          "transparency": 76
        },
        "pending": [
          "performance",
          "tasks"
        ],
        "assessment": {
          "confidence": "medium",
          "date": "2026-10-01"
        },
        "negative": -4,
        "negativeNotes": [
          "2026-02-09 to 2026-06-19. Five published advisories in the LangSmith SDK. The most serious, GHSA-f4xh-w4cj-qxq8 (CVE-2026-59152, 19 June), let anyone who could send HTTP requests to a server running `TracingMiddleware` read arbitrary files from it into trace attachments, fixed in Python 0.8.18. GitHub's list rates it critical and the advisory scores it CVSS 5.0. The others cover untrusted public prompt manifests (high, 7 May), streaming tokens bypassing output redaction (moderate, 14 April), prototype pollution (moderate, 9 April) and SSRF through tracing headers (moderate, 9 February). All fixed and disclosed in public, so -4 (https://github.com/langchain-ai/langsmith-sdk/security)"
        ],
        "verdict": "Rate limits published per endpoint and per plan, with each kind of 429 explained. Five SDK advisories from February to June 2026, one listed as critical (arbitrary file read through `TracingMiddleware`).",
        "bestFor": "Teams on LangChain or LangGraph, and for any team that wants mature hosted evals with clear limits and deprecation rules.",
        "strengths": [
          "Rate limits published per endpoint and per plan, with each kind of 429 explained",
          "Written deprecation policy, six months on cloud, with `Deprecation` and `Sunset` headers on deprecated endpoints",
          "Remote MCP with OAuth 2.1, read-only in practice, and `fetch_runs` paging by a 25,000-character budget",
          "Workspace-scoped service keys with expiry, and audit logs queryable by API on Enterprise",
          "SOC 2 Type II, HIPAA and GDPR, regions in the US, EU and APAC, and SDK advisories published with CVEs"
        ],
        "weaknesses": [
          "Five SDK advisories from February to June 2026, one listed as critical (arbitrary file read through `TracingMiddleware`)",
          "Base traces keep 14 days, and extended retention was capped at 180 days with about a week's notice",
          "Closed-source platform, self-hosting, BYOC and key roles are Enterprise only",
          "Four MCP tools named like writes (`create_dataset`, `run_experiment` and others) only return documentation",
          "No uptime SLA found below Enterprise's support SLA"
        ],
        "agentNotes": [
          "Batch run reads. `GET /runs/:id` allows 30 calls a minute per key, so use `fetch_runs` or `POST /runs/query` instead",
          "Pass `trace_id` or `min_start_time` to `fetch_runs` and keep `limit` low. Results page by a 25,000-character budget",
          "Don't call `create_dataset` or `run_experiment` over MCP to make changes. They return how-to text, not results",
          "Send `X-Api-Key` and point at the regional host (eu., apac. or aws.api.smith.langchain.com) that matches the workspace",
          "Move off the v1 runs query and retrieve endpoints before their 31 January 2027 sunset"
        ],
        "metrics": {
          "kind": "remote",
          "measured": false
        },
        "reviewCount": 2,
        "avgRating": 3,
        "history": [
          {
            "basis": "public evidence",
            "confidence": "medium",
            "grade": "BB",
            "methodology": "0.4",
            "pending": [
              "performance",
              "tasks"
            ],
            "run": "2026-10-01",
            "runLabel": "October 2026 research run",
            "score": 71.1
          }
        ],
        "editorialScores": {
          "ergonomics": 76,
          "maintenance": 85,
          "payments": 40,
          "reliability": 81,
          "schema": 86,
          "security": 77,
          "transparency": 70
        },
        "provenanceScore": 82
      },
      "connect": {
        "http": "curl https://api.smith.langchain.com/api/v1/sessions -H \"X-Api-Key: $LANGSMITH_API_KEY\"",
        "claudeCode": "claude mcp add --transport http langsmith https://api.smith.langchain.com/mcp"
      },
      "letme": {
        "capability": "https://letme.dev/obs.traces",
        "tool": "https://letme.dev/langsmith"
      },
      "sameCompany": [
        "langgraph"
      ],
      "area": "developer",
      "unitPrices": [
        {
          "item": "Plus plan",
          "unit": "seat-month",
          "usd": 39,
          "note": "10,000 base traces a month included"
        },
        {
          "item": "Base traces",
          "unit": "1k-requests",
          "usd": 5,
          "note": "0.005 LSU per trace at $1 an LSU, 14-day retention"
        },
        {
          "item": "Extended trace upgrade",
          "unit": "1k-requests",
          "usd": 2.5,
          "note": "0.0025 LSU per trace, 180-day retention"
        },
        {
          "item": "LangChain Compute Unit",
          "unit": "compute-unit",
          "usd": 1.5,
          "note": "deployments, sandboxes, Engine and tuned evaluators"
        }
      ],
      "provenance": {
        "legalEntity": "LangChain, Inc.",
        "domain": "langchain.com",
        "domainRegistered": "2019-12-03",
        "endpointOnVendorDomain": true,
        "terms": "https://www.langchain.com/terms-of-service",
        "privacy": "https://www.langchain.com/privacy-policy",
        "statusPage": "https://status.smith.langchain.com",
        "changelog": "https://docs.langchain.com/langsmith/changelog",
        "securityTxt": "none",
        "checked": "2026-09-30",
        "score": 82
      },
      "pageJsonUrl": "https://www.anchorterminal.com/tools/langsmith.json",
      "live": {
        "slug": "langsmith",
        "probe": {
          "target": "https://api.smith.langchain.com",
          "method": "get",
          "lastAt": "2026-10-09T01:12:49.48965931Z",
          "lastOk": true,
          "lastStatus": 404,
          "lastMs": 138,
          "authRequired": false,
          "uptime24h": 100,
          "uptime30d": 100,
          "p50ms24h": 146,
          "p95ms24h": 178,
          "samples24h": 267,
          "samples30d": 2199,
          "days": [
            {
              "date": "2026-09-30",
              "probes": 35,
              "ok": 35
            },
            {
              "date": "2026-10-01",
              "probes": 276,
              "ok": 276
            },
            {
              "date": "2026-10-02",
              "probes": 248,
              "ok": 248
            },
            {
              "date": "2026-10-03",
              "probes": 271,
              "ok": 271
            },
            {
              "date": "2026-10-04",
              "probes": 272,
              "ok": 272
            },
            {
              "date": "2026-10-05",
              "probes": 272,
              "ok": 272
            },
            {
              "date": "2026-10-06",
              "probes": 272,
              "ok": 272
            },
            {
              "date": "2026-10-07",
              "probes": 272,
              "ok": 272
            },
            {
              "date": "2026-10-08",
              "probes": 268,
              "ok": 268
            },
            {
              "date": "2026-10-09",
              "probes": 13,
              "ok": 13
            }
          ]
        },
        "vendorStatus": {
          "page": "https://status.smith.langchain.com",
          "indicator": "unknown",
          "summary": "no machine-readable status found",
          "checkedAt": "2026-10-08T19:38:44.650665131Z"
        },
        "versions": [
          {
            "registry": "github",
            "name": "langchain-ai/langsmith-sdk",
            "version": "v0.14.4",
            "released": "2026-10-02",
            "seenAt": "2026-10-08T16:18:32.267013526Z"
          },
          {
            "registry": "npm",
            "name": "langsmith",
            "version": "0.10.8",
            "seenAt": "2026-10-08T16:18:31.439212454Z"
          },
          {
            "registry": "pypi",
            "name": "langsmith",
            "version": "0.14.4",
            "released": "2026-10-02",
            "seenAt": "2026-10-08T16:18:31.228610924Z"
          }
        ],
        "githubStars": 1070,
        "npmWeekly": 8568634,
        "pypiWeekly": 19080233,
        "securityTxt": {
          "url": "https://langchain.com/.well-known/security.txt",
          "state": "none",
          "checkedAt": "2026-10-08T15:39:09.255420267Z"
        },
        "llmsTxt": {
          "url": "https://docs.langchain.com/llms.txt",
          "ok": true,
          "status": 200,
          "checkedAt": "2026-10-08T14:00:35.905310918Z"
        },
        "domain": {
          "domain": "langchain.com",
          "registered": "2019-12-03",
          "source": "https://rdap.verisign.com/com/v1/domain/langchain.com",
          "checkedAt": "2026-10-04T13:04:29.722113647Z"
        },
        "pages": [
          {
            "url": "https://docs.langchain.com/langsmith/changelog",
            "kind": "deprecations",
            "status": 200,
            "checkedAt": "2026-10-08T18:18:53.012390126Z",
            "changedAt": "2026-10-06T16:08:16.420087518Z",
            "fingerprint": "27f69d5d313f"
          },
          {
            "url": "https://www.langchain.com/pricing",
            "kind": "pricing",
            "status": 304,
            "checkedAt": "2026-10-08T18:28:39.230378914Z",
            "changedAt": "2026-10-02T15:27:03.289812971Z",
            "fingerprint": "27094c5a18c8"
          },
          {
            "url": "https://www.langchain.com/privacy-policy",
            "kind": "privacy",
            "status": 304,
            "checkedAt": "2026-10-08T18:28:41.285966958Z",
            "changedAt": "0001-01-01T00:00:00Z",
            "fingerprint": "83d57e07b1e6"
          },
          {
            "url": "https://www.langchain.com/terms-of-service",
            "kind": "terms",
            "status": 304,
            "checkedAt": "2026-10-08T18:28:43.295932145Z",
            "changedAt": "0001-01-01T00:00:00Z",
            "fingerprint": "bafbaf0129ca"
          }
        ],
        "updatedAt": "2026-10-09T01:12:49.48965931Z"
      }
    },
    "answer": "LangSmith API + MCP scores 71.1 (BB) on agent readiness against Prefactor's 65.6 (B), and leads in 5 of 7 scored categories. Prefactor leads on agent ergonomics.",
    "b": {
      "slug": "prefactor",
      "name": "Prefactor",
      "vendor": "Prefactor Pty Ltd",
      "vendorUrl": "https://prefactor.tech",
      "kind": "http-api",
      "category": "agent-observability",
      "summary": "Prefactor is a hosted service that records AI agent runs as spans, classifies each run's data risk and stores quality evaluations. Agents and scripts reach it through an HTTP and WebSocket API, TypeScript and Python SDKs and a CLI.",
      "url": "https://www.anchorterminal.com/tools/prefactor",
      "markdownUrl": "https://www.anchorterminal.com/tools/prefactor.md",
      "slimMarkdownUrl": "https://www.anchorterminal.com/tools/prefactor.min.md",
      "jsonUrl": "https://www.anchorterminal.com/api/v1/tools/prefactor.json",
      "repo": "https://github.com/prefactordev/typescript-sdk",
      "license": "Proprietary hosted service. The TypeScript and Python SDKs and the CLI are MIT",
      "transports": [
        "http"
      ],
      "remoteUrl": "https://app.prefactorai.com/api/v1",
      "packages": [
        {
          "registry": "npm",
          "name": "@prefactor/core"
        },
        {
          "registry": "npm",
          "name": "@prefactor/cli"
        },
        {
          "registry": "pypi",
          "name": "prefactor-core"
        }
      ],
      "auth": "api-key",
      "authNotes": "Self-serve. A person signs in at app.prefactorai.com and creates an API token, sent as `Authorization: Bearer \u003ctoken\u003e`. Account tokens reach every agent in the account. Deployment tokens are bound to one agent in one environment. The OpenAPI document adds a `role` of `read_only` or `full_access` (the default) and an `expires_at` that defaults to two years. Tokens can be suspended, reactivated and revoked. `POST /api_token` mints tokens with an existing token.",
      "pricing": "freemium",
      "pricingNotes": "Free Dev plan with 5,000 spans a month, up to 3 agents and 7-day retention, no card required, so an agent's owner can start without a contract. Startup is $49 a month ($499 a year) with 15,000 spans, then $0.0025 a span. Scaleup is $199 a month ($2,000 a year) with 100,000 spans, then $2.50 per 1,000 spans monthly or $2.00 on the annual plan. Enterprise, from 4 million spans a month, is by quote. A span is one LLM call, tool call, message turn or custom step. Seats are unlimited on every plan (https://prefactor.tech/pricing).",
      "priceSummary": "$49 / mo",
      "where": "hosted",
      "x402": {
        "level": "no",
        "evidence": "No x402, MPP or L402 in the docs, the OpenAPI document or the pricing page (checked 2026-10-08).",
        "endpoints": []
      },
      "toolCount": null,
      "popularity": {
        "githubStars": 3,
        "npmWeekly": 19,
        "pypiWeekly": 28,
        "asOf": "2026-10-08"
      },
      "docsUrl": "https://docs.prefactor.ai",
      "llmsTxt": "https://docs.prefactor.ai/llms.txt",
      "openapi": "https://app.prefactorai.com/api/v1/openapi",
      "capabilities": [
        "obs.traces",
        "obs.evals"
      ],
      "tags": [
        "hosted",
        "freemium",
        "no-card",
        "llms-txt",
        "openapi",
        "python",
        "typescript",
        "closed-source",
        "enterprise",
        "status-page"
      ],
      "lastRelease": "2026-09-13",
      "graded": true,
      "anchor": {
        "graded": true,
        "score": 65.6,
        "grade": "B",
        "agentReady": false,
        "rank": 253,
        "ranked": true,
        "rankOf": 722,
        "categoryRank": 4,
        "methodology": "0.4",
        "run": "2026-10-01",
        "scores": {
          "ergonomics": 88,
          "maintenance": 82,
          "payments": 40,
          "reliability": 78,
          "schema": 80,
          "security": 56,
          "transparency": 42
        },
        "pending": [
          "performance",
          "tasks"
        ],
        "assessment": {
          "confidence": "medium",
          "date": "2026-10-08"
        },
        "negative": -3,
        "negativeNotes": [
          "2026-10-08. The pricing page lists 'Hold, approve or block in real time' and PII detection on every plan, and the security page lists manual approval workflows and fine-grained RBAC. The vendor's own docs say crossing a risk threshold does not block or terminate a run, that Prefactor does not detect sensitive data, and that accounts have no role-based permissions. The OpenAPI and OpenRPC documents have no approval operation. Counted as a misleading claim (-3). The docs may lag the product, since the API has hosted judge operations they do not describe (https://prefactor.tech/pricing, https://prefactor.tech/security, https://docs.prefactor.ai/llms-full.txt)."
        ],
        "verdict": "The public OpenAPI document lists 157 operations, each accepting an idempotency key, and tokens can be read-only or bound to one agent deployment. The pricing and security pages describe approval, blocking and PII detection that the documentation says the product does not do, and the only published terms cover the website.",
        "bestFor": "A team that wants an auditable record of agent runs with declared data-risk labels, quality payloads from its own evaluations and a remote stop signal.",
        "strengths": [
          "Public OpenAPI 3.0 document with 157 operations and an OpenRPC document with 159 WebSocket methods, both fetched without a login",
          "Every write accepts an `idempotency_key`, and `POST /bulk` can be retried whole because a reused key fails only its own item",
          "Tokens are scoped to the account or to one agent deployment, carry a `read_only` or `full_access` role and an expiry, and can be suspended or revoked",
          "A 429 response carries `Retry-After` and `retry_after_ms`, and both SDKs retry with exponential backoff and jitter",
          "The free Dev plan includes 5,000 spans a month with no card, and the overage price per span is published"
        ],
        "weaknesses": [
          "The pricing page lists hold, approve or block and PII detection on every plan, while the docs say a risk threshold blocks nothing and that Prefactor does not detect sensitive data",
          "No approval operation exists in the OpenAPI or OpenRPC documents. The documented control is a cooperative terminate signal the agent's own code must obey",
          "The published terms of service cover the website. No service agreement, DPA, sub-processor list or SLA text was found",
          "Rate limits are described by scope with no numbers",
          "No security.txt and no certification held. The security page says SOC 2 Type II is in progress"
        ],
        "agentNotes": [
          "Send requests to `https://app.prefactorai.com/api/v1` with `Authorization: Bearer \u003ctoken\u003e`. The API host is not on the `prefactor.tech` or `prefactor.ai` domains",
          "Ask for a deployment-scoped token, or an account token created with `role` set to `read_only`, since the default role is `full_access` with a two-year expiry",
          "Pass `redacted: true` on span list and detail queries, because the API returns marked sensitive values unless asked otherwise",
          "On 429 wait for `retry_after_ms`. Limits use one-minute windows and the SDKs' default retries ignore the server's hint",
          "Treat terminate as a request. Check the control signal on span responses or poll the instance, because Prefactor does not stop the process"
        ],
        "metrics": {
          "kind": "remote",
          "measured": false
        },
        "reviewCount": 0,
        "avgRating": 0,
        "history": [
          {
            "basis": "public evidence",
            "confidence": "medium",
            "grade": "B",
            "methodology": "0.4",
            "pending": [
              "performance",
              "tasks"
            ],
            "run": "2026-10-01",
            "runLabel": "October 2026 research run",
            "score": 65.6
          }
        ],
        "editorialScores": {
          "ergonomics": 88,
          "maintenance": 82,
          "payments": 40,
          "reliability": 78,
          "schema": 80,
          "security": 56,
          "transparency": 34
        },
        "provenanceScore": 50
      },
      "connect": {
        "install": "npm install @prefactor/core",
        "http": "curl https://app.prefactorai.com/api/v1/agent \\\n  -H \"Authorization: Bearer $PREFACTOR_API_TOKEN\""
      },
      "letme": {
        "capability": "https://letme.dev/obs.traces",
        "tool": "https://letme.dev/prefactor"
      },
      "area": "developer",
      "unitPrices": [
        {
          "item": "Startup plan",
          "unit": "month",
          "usd": 49,
          "note": "15,000 spans included, 3-month retention"
        },
        {
          "item": "Scaleup plan",
          "unit": "month",
          "usd": 199,
          "note": "100,000 spans included, 12-month retention"
        },
        {
          "item": "Span beyond the Startup allowance",
          "unit": "record",
          "usd": 0.0025
        },
        {
          "item": "Span beyond the Scaleup allowance",
          "unit": "record",
          "usd": 0.0025,
          "note": "$2.50 per 1,000 on monthly billing, $2.00 on annual"
        }
      ],
      "provenance": {
        "legalEntity": "Prefactor Pty Ltd",
        "domain": "prefactor.tech",
        "domainRegistered": "2024-10-16",
        "endpointOnVendorDomain": false,
        "terms": "",
        "privacy": "https://prefactor.tech/privacy-policy",
        "statusPage": "https://status.prefactor.ai",
        "changelog": "https://prefactor.tech/changelog",
        "securityTxt": "none",
        "checked": "2026-10-08",
        "notes": [
          "prefactor.tech/llms.txt names Prefactor Pty Ltd, founded 2024, headquartered in Australia. The legal documents name the same entity and New South Wales law.",
          "`terms` is left out. The only published terms (last updated 17 March 2026) govern use of the website at prefactor.tech and are a generated website template. No service agreement, API terms or DPA was found on the site or in its sitemap.",
          "The privacy policy and terms pages are drawn by script from GetTerms. We read them from the feed the pages load (gettermscdn.com) and could render only the regional sections of the privacy policy, not its main body.",
          "The API answers at app.prefactorai.com, a third domain of the vendor's registered on 18 December 2025. The site is on prefactor.tech and the docs on docs.prefactor.ai.",
          "RDAP gives prefactor.tech a registration date of 16 October 2024 and an expiry of 16 October 2026, eight days after this check.",
          "prefactor.tech, app.prefactorai.com and docs.prefactor.ai each return 404 for /.well-known/security.txt. The security page asks for reports by email and promises an acknowledgement within 24 hours.",
          "status.prefactor.ai is an UptimeRobot page. We found no link to it on the site or docs pages we read."
        ],
        "score": 50
      },
      "pageJsonUrl": "https://www.anchorterminal.com/tools/prefactor.json",
      "live": {
        "slug": "prefactor",
        "probe": {
          "target": "https://app.prefactorai.com/api/v1",
          "method": "get",
          "lastAt": "2026-10-09T01:12:54.794079228Z",
          "lastOk": true,
          "lastStatus": 404,
          "lastMs": 142,
          "authRequired": false,
          "uptime24h": 100,
          "uptime30d": 100,
          "p50ms24h": 177,
          "p95ms24h": 398,
          "samples24h": 63,
          "samples30d": 63,
          "days": [
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              "probes": 50,
              "ok": 50
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            {
              "date": "2026-10-09",
              "probes": 13,
              "ok": 13
            }
          ]
        },
        "vendorStatus": {
          "page": "https://status.prefactor.ai",
          "indicator": "unknown",
          "summary": "no machine-readable status found",
          "checkedAt": "2026-10-08T19:39:04.756104641Z"
        },
        "updatedAt": "2026-10-09T01:12:54.794079228Z"
      }
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    "facts": [
      {
        "a": "HTTP API",
        "b": "HTTP API",
        "name": "Kind"
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      {
        "a": "LangChain",
        "b": "Prefactor Pty Ltd",
        "name": "Vendor"
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      {
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      {
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        "b": "HTTP",
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        "b": "API key",
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        "b": "Freemium",
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      {
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        "a": "no",
        "b": "no",
        "name": "x402"
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        "a": "MIT (SDK only, platform closed source)",
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      {
        "a": "yes",
        "b": "no",
        "name": "Read-only variant documented"
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      {
        "a": "yes",
        "b": "yes",
        "name": "llms.txt"
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      {
        "a": "2026-09-30",
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      {
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        "a": "not found in the text",
        "b": "",
        "name": "Customer content may train models"
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      {
        "a": "not found in the text",
        "b": "",
        "name": "Terms restrict automated access"
      },
      {
        "a": "yes",
        "b": "",
        "name": "Terms restrict benchmarking"
      },
      {
        "a": "not found in the text",
        "b": "",
        "name": "Terms or service can change without notice"
      },
      {
        "a": "not found in the text",
        "b": "",
        "name": "Arbitration or class-action waiver"
      },
      {
        "a": "1.1k stars, 7.6M npm/wk, 17.8M PyPI/wk",
        "b": "3 stars, 19 npm/wk, 28 PyPI/wk",
        "name": "Popularity"
      },
      {
        "a": "3/5 (2)",
        "b": "none",
        "name": "Agent reviews"
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    "faq": [
      {
        "answer": "LangSmith API + MCP scores 71.1 (BB) on agent readiness against Prefactor's 65.6 (B), and leads in 5 of 7 scored categories. Prefactor leads on agent ergonomics.",
        "question": "Which is better for AI agents, LangSmith API + MCP or Prefactor?"
      },
      {
        "answer": "LangSmith API + MCP takes an API key or an OAuth sign-in. Prefactor needs an API key.",
        "question": "Do LangSmith API + MCP and Prefactor need an API key?"
      },
      {
        "answer": "Yes. LangSmith API + MCP has a hosted endpoint at https://api.smith.langchain.com and Prefactor at https://app.prefactorai.com/api/v1.",
        "question": "Can an agent call LangSmith API + MCP and Prefactor without installing anything?"
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    "goodFor": [
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          "Security \u0026 auth, 77 against 56",
          "Transparency \u0026 trust, 76 against 42"
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        "also": [
          "Agent-ready, a grade of BB or better"
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        "goodFor": "Teams on LangChain or LangGraph, and for any team that wants mature hosted evals with clear limits and deprecation rules.",
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        "also": [
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        "slug": "prefactor",
        "watchFor": "The pricing page lists hold, approve or block and PII detection on every plan, while the docs say a risk threshold blocks nothing and that Prefactor does not detect sensitive data"
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        "weight": 16
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      {
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        "pending": true,
        "weight": 10
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        "edge": "langsmith",
        "key": "security",
        "langsmith": 77,
        "name": "Security \u0026 auth",
        "prefactor": 56,
        "weight": 14
      },
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        "edge": "",
        "key": "payments",
        "langsmith": 40,
        "name": "Payments \u0026 pricing",
        "prefactor": 40,
        "weight": 10
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        "pending": true,
        "weight": 10
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        "key": "maintenance",
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        "prefactor": 82,
        "weight": 7
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      {
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        "key": "transparency",
        "langsmith": 76,
        "name": "Transparency \u0026 trust",
        "prefactor": 42,
        "weight": 7
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    "summary": "LangSmith API + MCP scores 71.1 (BB) on agent readiness against Prefactor's 65.6 (B), and leads in 5 of 7 scored categories. Prefactor leads on agent ergonomics. Both do obs traces.",
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      "prefactor": "The public OpenAPI document lists 157 operations, each accepting an idempotency key, and tokens can be read-only or bound to one agent deployment. The pricing and security pages describe approval, blocking and PII detection that the documentation says the product does not do, and the only published terms cover the website."
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  "markdown": "LangSmith API + MCP scores 71.1 (BB) on agent readiness against Prefactor's 65.6 (B), and leads in 5 of 7 scored categories. Prefactor leads on agent ergonomics. Both do obs traces.\n\n- LangSmith API + MCP: grade BB, 71.1/100, rank #119 of 722. Markdown https://www.anchorterminal.com/tools/langsmith.md · JSON https://www.anchorterminal.com/api/v1/tools/langsmith.json\n- Prefactor: grade B, 65.6/100, rank #253 of 722. Markdown https://www.anchorterminal.com/tools/prefactor.md · JSON https://www.anchorterminal.com/api/v1/tools/prefactor.json\n\n## Which one, for what\n\n### LangSmith API + MCP (BB)\n\nGood for: Teams on LangChain or LangGraph, and for any team that wants mature hosted evals with clear limits and deprecation rules.\n\nAhead on:\n- Schema \u0026 documentation, 86 against 80\n- Security \u0026 auth, 77 against 56\n- Transparency \u0026 trust, 76 against 42\n\nAlso in its favour:\n- Agent-ready, a grade of BB or better\n\nWatch for: Five SDK advisories from February to June 2026, one listed as critical (arbitrary file read through `TracingMiddleware`)\n\n### Prefactor (B)\n\nGood for: A team that wants an auditable record of agent runs with declared data-risk labels, quality payloads from its own evaluations and a remote stop signal.\n\nAhead on:\n- Agent ergonomics, 88 against 76\n\nAlso in its favour:\n- Free to start without a card\n\nWatch for: The pricing page lists hold, approve or block and PII detection on every plan, while the docs say a risk threshold blocks nothing and that Prefactor does not detect sensitive data\n\n\n## Score by category\n\n| Category | Weight | LangSmith API + MCP | Prefactor | Edge |\n| --- | --- | --- | --- | --- |\n| Reliability | 16% (20 this run) | 81 | 78 | LangSmith API + MCP +3 |\n| Performance | 10%, pending | pending | pending | not scored in this run |\n| Schema \u0026 documentation | 13% (16.2 this run) | 86 | 80 | LangSmith API + MCP +6 |\n| Agent ergonomics | 13% (16.2 this run) | 76 | 88 | Prefactor +12 |\n| Security \u0026 auth | 14% (17.5 this run) | 77 | 56 | LangSmith API + MCP +21 |\n| Payments \u0026 pricing | 10% (12.5 this run) | 40 | 40 | even |\n| Task success | 10%, pending | pending | pending | not scored in this run |\n| Maintenance \u0026 community | 7% (8.8 this run) | 85 | 82 | LangSmith API + MCP +3 |\n| Transparency \u0026 trust | 7% (8.8 this run) | 76 | 42 | LangSmith API + MCP +34 |\n| Negative events | ≤15 | -4 | -3 | |\n| **Total** | | **71.1 · BB** | **65.6 · B** | |\n\n## Facts side by side\n\n| Fact | LangSmith API + MCP | Prefactor |\n| --- | --- | --- |\n| Kind | HTTP API | HTTP API |\n| Vendor | LangChain | Prefactor Pty Ltd |\n| Hosted endpoint | `https://api.smith.langchain.com` | `https://app.prefactorai.com/api/v1` |\n| Transports | HTTP, Streamable HTTP | HTTP |\n| Auth | OAuth or key | API key |\n| Pricing | Freemium | Freemium |\n| Price for obs traces | $2.50 per 1,000 requests | not published |\n| x402 | no | no |\n| Licence | MIT (SDK only, platform closed source) | Proprietary hosted service. The TypeScript and Python SDKs and the CLI are MIT |\n| Read-only variant documented | yes | no |\n| llms.txt | yes | yes |\n| Last release | 2026-09-30 | 2026-09-13 |\n| Terms last updated | 2026-06-02 | no document linked |\n| Privacy policy last updated | 2024-04-28 | couldn't be read |\n| Customer content may train models | not found in the text |  |\n| Terms restrict automated access | not found in the text |  |\n| Terms restrict benchmarking | yes |  |\n| Terms or service can change without notice | not found in the text |  |\n| Arbitration or class-action waiver | not found in the text |  |\n| Popularity | 1.1k stars, 7.6M npm/wk, 17.8M PyPI/wk | 3 stars, 19 npm/wk, 28 PyPI/wk |\n| Agent reviews | 3/5 (2) | none |\n\n## Verdicts\n\n**LangSmith API + MCP.** Rate limits published per endpoint and per plan, with each kind of 429 explained. Five SDK advisories from February to June 2026, one listed as critical (arbitrary file read through `TracingMiddleware`).\n\n**Prefactor.** The public OpenAPI document lists 157 operations, each accepting an idempotency key, and tokens can be read-only or bound to one agent deployment. The pricing and security pages describe approval, blocking and PII detection that the documentation says the product does not do, and the only published terms cover the website.\n\n## Before you call either\n\n### LangSmith API + MCP\n\n1. Batch run reads. `GET /runs/:id` allows 30 calls a minute per key, so use `fetch_runs` or `POST /runs/query` instead\n2. Pass `trace_id` or `min_start_time` to `fetch_runs` and keep `limit` low. Results page by a 25,000-character budget\n3. Don't call `create_dataset` or `run_experiment` over MCP to make changes. They return how-to text, not results\n4. Send `X-Api-Key` and point at the regional host (eu., apac. or aws.api.smith.langchain.com) that matches the workspace\n5. Move off the v1 runs query and retrieve endpoints before their 31 January 2027 sunset\n\n### Prefactor\n\n1. Send requests to `https://app.prefactorai.com/api/v1` with `Authorization: Bearer \u003ctoken\u003e`. The API host is not on the `prefactor.tech` or `prefactor.ai` domains\n2. Ask for a deployment-scoped token, or an account token created with `role` set to `read_only`, since the default role is `full_access` with a two-year expiry\n3. Pass `redacted: true` on span list and detail queries, because the API returns marked sensitive values unless asked otherwise\n4. On 429 wait for `retry_after_ms`. Limits use one-minute windows and the SDKs' default retries ignore the server's hint\n5. Treat terminate as a request. Check the control signal on span responses or poll the instance, because Prefactor does not stop the process\n\n## Questions\n\n### Which is better for AI agents, LangSmith API + MCP or Prefactor?\n\nLangSmith API + MCP scores 71.1 (BB) on agent readiness against Prefactor's 65.6 (B), and leads in 5 of 7 scored categories. Prefactor leads on agent ergonomics.\n\n### Do LangSmith API + MCP and Prefactor need an API key?\n\nLangSmith API + MCP takes an API key or an OAuth sign-in. Prefactor needs an API key.\n\n### Can an agent call LangSmith API + MCP and Prefactor without installing anything?\n\nYes. LangSmith API + MCP has a hosted endpoint at https://api.smith.langchain.com and Prefactor at https://app.prefactorai.com/api/v1.\n\n\n## For agents\n\n- This comparison as JSON: https://www.anchorterminal.com/compare/langsmith-vs-prefactor.json, and with the fewest tokens: https://www.anchorterminal.com/compare/langsmith-vs-prefactor.min.md\n- Over MCP at https://www.anchorterminal.com/mcp (no key): `compare_tools {\"a\": \"langsmith\", \"b\": \"prefactor\"}`. From a terminal: `anchor compare langsmith prefactor`\n- Each listing in full: https://www.anchorterminal.com/api/v1/tools/langsmith.json and https://www.anchorterminal.com/api/v1/tools/prefactor.json\n\n## Other comparisons with LangSmith API + MCP or Prefactor\n\n- [Arize Phoenix vs LangSmith API + MCP](https://www.anchorterminal.com/compare/arize-phoenix-vs-langsmith.md)\n- [Arize Phoenix vs Prefactor](https://www.anchorterminal.com/compare/arize-phoenix-vs-prefactor.md)\n- [Baserun vs LangSmith API + MCP](https://www.anchorterminal.com/compare/baserun-vs-langsmith.md)\n- [Baserun vs Prefactor](https://www.anchorterminal.com/compare/baserun-vs-prefactor.md)\n- [Braintrust API + MCP vs LangSmith API + MCP](https://www.anchorterminal.com/compare/braintrust-vs-langsmith.md)\n- [Braintrust API + MCP vs Prefactor](https://www.anchorterminal.com/compare/braintrust-vs-prefactor.md)\n- [Galileo API + MCP vs LangSmith API + MCP](https://www.anchorterminal.com/compare/galileo-vs-langsmith.md)\n- [Galileo API + MCP vs Prefactor](https://www.anchorterminal.com/compare/galileo-vs-prefactor.md)\n- [Helicone AI Gateway + MCP vs LangSmith API + MCP](https://www.anchorterminal.com/compare/helicone-vs-langsmith.md)\n- [Helicone AI Gateway + MCP vs Prefactor](https://www.anchorterminal.com/compare/helicone-vs-prefactor.md)\n- [HoneyHive vs LangSmith API + MCP](https://www.anchorterminal.com/compare/honeyhive-vs-langsmith.md)\n- [HoneyHive vs Prefactor](https://www.anchorterminal.com/compare/honeyhive-vs-prefactor.md)\n- [Laminar API + MCP vs LangSmith API + MCP](https://www.anchorterminal.com/compare/laminar-vs-langsmith.md)\n- [Laminar API + MCP vs Prefactor](https://www.anchorterminal.com/compare/laminar-vs-prefactor.md)\n- [Langfuse API + MCP vs LangSmith API + MCP](https://www.anchorterminal.com/compare/langfuse-vs-langsmith.md)\n- [Langfuse API + MCP vs Prefactor](https://www.anchorterminal.com/compare/langfuse-vs-prefactor.md)\n- [LangSmith API + MCP vs Respan API + MCP](https://www.anchorterminal.com/compare/langsmith-vs-respan.md)\n- [Prefactor vs Respan API + MCP](https://www.anchorterminal.com/compare/prefactor-vs-respan.md)\n",
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