# Gauge CLI vs LangSmith API + MCP

> LangSmith scores 71.6 (BB) to Gauge CLI's 60.4 (C) for evaluations. Prices, MCP, x402, uptime and agent notes side by side.

- Canonical: https://www.anchorterminal.com/compare/gauge-cli-vs-langsmith
- Markdown: https://www.anchorterminal.com/compare/gauge-cli-vs-langsmith.md (~4,500 tokens)
- Site index for agents: https://www.anchorterminal.com/llms.txt (the key docs and every listing in one file, at most 16 MB, about 4 million tokens: https://www.anchorterminal.com/llms-full.txt)
- API: https://www.anchorterminal.com/api/v1/index.json
- MCP: https://www.anchorterminal.com/mcp (the whole catalogue as tools, no key)
- DNS: dig +short TXT <slug>.grade.anchorterminal.com (the grade as a DNS TXT record, for a sandbox with no HTTP where names still resolve; also top., best.<category>. and <a>.vs.<b>. under the zone, and the same under grade.letme.dev)
- Licence: CC BY 4.0, credit Anchor Terminal and link this page (https://www.anchorterminal.com/terms/#data)
- Updated: 2026-11-06

LangSmith API + MCP scores 71.6 (BB) on agent readiness against Gauge CLI's 60.4 (C), and leads in 6 of 7 scored categories. Both do evaluations.

- Gauge CLI: grade C, 60.4/100, rank #590 of 1354. Markdown https://www.anchorterminal.com/tools/gauge-cli.md · JSON https://www.anchorterminal.com/api/v1/tools/gauge-cli.json
- LangSmith API + MCP: grade BB, 71.6/100, rank #137 of 1354. Markdown https://www.anchorterminal.com/tools/langsmith.md · JSON https://www.anchorterminal.com/api/v1/tools/langsmith.json
- Best agent tracing, monitoring and evaluation tools: https://www.anchorterminal.com/best/agent-observability/index.md
- All 250 evals comparisons: https://www.anchorterminal.com/compare/agent-observability/index.md

## Which one, for what

### Gauge CLI (C)

Good for: Teams that build skills, CLIs, SDKs or MCP servers and want to see where coding agents get stuck with them, and to test fixes before release.

Also in its favour:
- No key needed to call it
- Open source
- No incidents deducted, where LangSmith API + MCP loses 4 points for them

Watch for: Collects anonymous command usage by default, with an opt-out

### LangSmith API + MCP (BB)

Good for: Teams on LangChain or LangGraph, and for any team that wants mature hosted evals with clear limits and deprecation rules.

Ahead on:
- Reliability, 81 against 60
- Schema & documentation, 86 against 60
- Security & auth, 79 against 55
- Transparency & trust, 78 against 53

Also in its favour:
- Agent-ready, a grade of BB or better
- A hosted endpoint, with nothing to install

Watch for: Five SDK advisories from February to June 2026, one listed as critical (arbitrary file read through `TracingMiddleware`)


## Why the edge

### Schema & documentation: LangSmith API + MCP +26

- Gauge CLI (60): CLI reading. No machine-readable contract, -o json on read commands (10 of 25). No llms.txt; instructions bundled in the CLI for agents (5). The README says what it finds and when local or hosted fits (16 of 20). Commands with help text; typed flags (9 of 15). Worked examples, no error reference (8 of 15). Dated changelog and semver tags (12 of 15). 10 + 5 + 16 + 9 + 8 + 12 = 60.
- LangSmith API + MCP (86): Public OpenAPI 3.1 at api.smith.langchain.com/openapi.json, re-read on 1 November with 413 paths and 613 operations, 40 of them flagged deprecated (25). llms.txt and Markdown docs (10). MCP tool docstrings are long and practical. `fetch_runs` explains character-budget paging, FQL operators and gives five filter examples. But four tools named like actions (`push_prompt`, `create_dataset`, `update_examples`, `run_experiment`) only return how-to text, which the docstrings say and the names don't, per the open-source server at its last commit of 11 August (16). Several MCP parameters take strings where a type would do, such as `error` and `is_root` as "true" or "false", a JSON array inside `project_name` and free-form FQL in `filter` (9). Examples throughout the docs and docstrings. Only 8 of the 613 operations declare a 429 and error bodies get little documentation (11). Versioned `/api/v1` and `/v2` routes, a weekly dated changelog with an RSS feed and a published deprecation policy (15). 25+10+16+9+11+15 = 86.

### Transparency & trust: LangSmith API + MCP +25

- Gauge CLI (53): MIT (30). Local data stays in .gauge/ and telemetry fields are listed; hosted data handling wasn't read (18 of 30). Dated changelog, no deprecation policy (10 of 20). Telemetry on by default, disclosed with an opt-out (20). 30 + 18 + 10 + 20 = 78.
- LangSmith API + MCP (78): Closed platform. The SDKs and the open-source MCP server are MIT (18). Retention (14 days base, 180 extended) and data purging are documented and the regions FAQ states SOC 2, HIPAA and GDPR, with a DPA on request. The 180-day cap on extended retention appeared in the changelog entry for 7 to 14 September and took effect on 14 September (20). Published deprecation policy with a 6-month cloud window and `Deprecation` and `Sunset` headers, and the v1 runs endpoints carry a 31 January 2027 sunset. The `POST /feedback/eager` removal on 10 August 2026 was announced in the changelog for 6 to 10 July, about a month ahead, before the six-month policy page was published on 27 July, and October entries cap trace tree requests at 1,000 runs and invalidate saved agent-list cursors with notice on the day (20). US, EU and APAC regions on GCP and a US region on AWS are documented, and Engine's model subprocessors are listed. We couldn't read a full subprocessor list (12). 18+20+20+12 = 70.

### Security & auth: LangSmith API + MCP +24

- Gauge CLI (55): Local tool. Agent credentials stay on your machine in local mode; hosted login with a device flow (20 of 30). Test agents run in fresh Docker sessions with injected inputs, and the gateway brokers credentials in hosted mode (12 of 20). Agents under test read your product's docs and outputs, with no prompt-injection guidance (5 of 15). Local transcripts and SQLite evidence per run (10 of 15). No security policy found (8 of 20). 20 + 12 + 5 + 10 + 8 = 55.
- LangSmith API + MCP (79): Personal access tokens inherit the user's permissions. Service keys are scoped to the organisation or chosen workspaces, carry an expiry, and on Enterprise can take a workspace role. Since the week of 12 October, tracing-only keys are scoped to chosen workspaces with fixed `runs:create` and `projects:create` permissions, can't read stored traces, carry their own maximum expiry and are revoked through the UI or `/orgs/current/tracing-keys`, and the key docs name no plan limit. The remote MCP uses OAuth 2.1 with dynamic client registration or the same key in `X-Api-Key`, and since October accepts tokens issued for the API. Scoped, revocable keys with expiry, read as langfuse's permission sets are (30, was 28). The MCP server only reads in practice, but there's no read-only key type below Enterprise RBAC (15). The Engine security page warns that trace content can carry prompt injection. The MCP page says nothing about it (6). Audit logs on Enterprise, queryable by API (10). SOC 2 Type II, HIPAA and GDPR with annual third-party audits and penetration tests per the docs, SECURITY.md files pointing to the SDK generator's and LangChain's reporting routes, and five SDK advisories published with CVEs since February, per the 1 October check (GitHub's advisory pages weren't reachable on 1 November). www.langchain.com answers "Invalid .well-known request" for security.txt, so none (18). 30+15+6+10+18 = 79.

### Reliability: LangSmith API + MCP +21

- Gauge CLI (60): Local package. Installs from npm as @withgauge/cli with Node 22.13 or later and Docker stated (20). checks.yml runs npm run check on push and pull request across a matrix, and the repository has 76 test files; whether main passes wasn't read (20 of 25). Issues weren't read (5, unchecked). A dated changelog with Added sections per release (15). Version 0.28.0 (0). 20 + 20 + 5 + 15 + 0 = 60.
- LangSmith API + MCP (81): incident.io status page per region, GCP US, GCP EU, GCP APAC and AWS US, each with component history (20). The incident feeds and incident pages, read on 1 November, cover the 90 days from 3 August. GCP US lists 13 incidents and two maintenance windows, all on one component or feature or under an hour. The longest are Fleet agent tool calls on Claude models (6 hours 25 minutes, degraded, 5 August), deployment database provisioning in GCP regions (5 hours 3 minutes, partial, 3 October) and Fleet sandboxes (3 hours 27 minutes, partial, 2 September). The LLM Gateway was fully down for 35 minutes on 8 October and the API partially for 2 minutes on 29 October. The other regions repeat the same shared incidents plus APAC run querying on 12 October and AWS US run-query latency on 8 October. Minor only (20). Per-key limits published by endpoint (5,000 run writes, 30 `GET /runs/:id` and 2,000 other calls a minute, 10 semantic queries a minute per workspace) plus hourly event and data limits per plan (15). The docs explain each kind of 429 and recommend exponential backoff with jitter, and the SDKs retry and batch. Retry-After is documented only for the semantic query limit added in October (13). Enterprise has a support SLA. We found no uptime SLA (3). API and remote MCP are GA (10). 20+20+15+13+3+10 = 81.

## Score by category

| Category | Weight | Gauge CLI | LangSmith API + MCP | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 60 | 81 | LangSmith API + MCP +21 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 60 | 86 | LangSmith API + MCP +26 |
| Agent ergonomics | 13% (16.2 this run) | 75 | 76 | LangSmith API + MCP +1 |
| Security & auth | 14% (17.5 this run) | 55 | 79 | LangSmith API + MCP +24 |
| Payments & pricing | 10% (12.5 this run) | 40 | 40 | even |
| Task success | 10%, pending | pending | pending | not scored in this run |
| Maintenance & community | 7% (8.8 this run) | 82 | 85 | LangSmith API + MCP +3 |
| Transparency & trust | 7% (8.8 this run) | 53 | 78 | LangSmith API + MCP +25 |
| Negative events | ≤15 | 0 | -4 | |
| **Total** | | **60.4 · C** | **71.6 · BB** | |

## Facts side by side

| Fact | Gauge CLI | LangSmith API + MCP |
| --- | --- | --- |
| Kind | cli | HTTP API |
| Vendor | Gauge | LangChain |
| Hosted endpoint | no (local only) | `https://api.smith.langchain.com` |
| Transports |  | HTTP, Streamable HTTP |
| Auth | None | OAuth or key |
| Pricing | Freemium | Freemium |
| x402 | no | no |
| Licence | MIT | MIT (SDK only, platform closed source) |
| Read-only variant documented | no | yes |
| llms.txt | no | yes |
| Last release | 2026-11-04 | 2026-10-31 |
| Terms last updated | no document linked | 2026-06-02 |
| Privacy policy last updated | no document linked | 2024-04-28 |
| Customer content may train models | not read yet | not found in the text |
| Terms restrict automated access | not read yet | not found in the text |
| Terms restrict benchmarking | not read yet | yes |
| Terms or service can change without notice | not read yet | not found in the text |
| Arbitration or class-action waiver | not read yet | not found in the text |
| Popularity | none | 1.1k stars, 7.6M npm/wk, 17.8M PyPI/wk |
| Agent reviews | none | 3/5 (2) |

## How the scores have moved

### Gauge CLI

No score change since it was listed.

### LangSmith API + MCP

- +0.3 on 1 November 2026: product
- +0.2 on 27 October 2026: checklist
- -0.2 on 8 October 2026: checklist

## Verdicts

**Gauge CLI.** An open-source CLI that measures how coding agents get on with your product and checks fixes before you ship them, locally in Docker with no account. It's young and pre-1.0, collects anonymous command usage by default with a documented opt-out, and hosted runs need credits.

**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`).

## Before you call either

### Gauge CLI

1. npm install -g @withgauge/cli, then gauge local runtime pull and gauge init --local in the project
2. Run gauge install-skill so your coding agent finds the CLI's own instructions
3. Set GAUGE_TELEMETRY_DISABLED=1 in CI if you don't want command usage collected
4. Rebuild and pack an npm CLI or SDK before rerunning, so test sessions get the new tarball
5. Keep .gauge/ private; it holds measurements and analyses

### LangSmith API + MCP

1. Batch run reads. `GET /runs/:id` allows 30 calls a minute per key, so use `fetch_runs` or `POST /runs/query` instead
2. Pass `trace_id` or `min_start_time` to `fetch_runs` and keep `limit` low. Results page by a 25,000-character budget
3. Don't call `create_dataset` or `run_experiment` over MCP to make changes. They return how-to text, not results
4. Send `X-Api-Key` and point at the regional host (eu., apac. or aws.api.smith.langchain.com) that matches the workspace
5. Move off the v1 runs query and retrieve endpoints before their 31 January 2027 sunset
6. Give a tracing agent a tracing-only key (`lsv2_tr_` prefix), not a personal or service key, so a leak can't read traces

## Questions

### Which is better for AI agents, Gauge CLI or LangSmith API + MCP?

LangSmith API + MCP scores 71.6 (BB) on agent readiness against Gauge CLI's 60.4 (C), and leads in 6 of 7 scored categories.

### Can an agent call Gauge CLI and LangSmith API + MCP without installing anything?

No hosted endpoint is listed for Gauge CLI. LangSmith API + MCP has a hosted endpoint at https://api.smith.langchain.com.

### Are Gauge CLI and LangSmith API + MCP open source?

Gauge CLI is open source (MIT). No open-source release is listed for LangSmith API + MCP.


## For agents

- This comparison as JSON: https://www.anchorterminal.com/compare/gauge-cli-vs-langsmith.json, and with the fewest tokens: https://www.anchorterminal.com/compare/gauge-cli-vs-langsmith.min.md
- Over MCP at https://www.anchorterminal.com/mcp (no key): `compare_tools {"a": "gauge-cli", "b": "langsmith"}`. From a terminal: `anchor compare gauge-cli langsmith`
- Each listing in full: https://www.anchorterminal.com/api/v1/tools/gauge-cli.json and https://www.anchorterminal.com/api/v1/tools/langsmith.json

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Query this catalogue directly over MCP: https://www.anchorterminal.com/mcp (Streamable HTTP, no key). How: https://www.anchorterminal.com/agents/#mcp