# LangSmith API + MCP vs LangWatch

> LangSmith API + MCP scores 71.1 (BB) on agent readiness against LangWatch's 65.5 (B), and leads in 4 of 7 scored categories. LangWatch leads on maintenance & community. Both do obs traces. Category scores, facts, verdicts and agent notes side by side.

- Canonical: https://www.anchorterminal.com/compare/langsmith-vs-langwatch
- Markdown: https://www.anchorterminal.com/compare/langsmith-vs-langwatch.md (~2,550 tokens)
- Slim: https://www.anchorterminal.com/compare/langsmith-vs-langwatch.min.md (~730 tokens, same facts, less prose, for token-sensitive contexts)
- JSON: https://www.anchorterminal.com/compare/langsmith-vs-langwatch.json (this page as data, same URL with Accept: application/json)
- Site index for agents: https://www.anchorterminal.com/llms.txt (full text: https://www.anchorterminal.com/llms-full.txt)
- API: https://www.anchorterminal.com/api/v1/index.json
- Updated: 2026-10-09

LangSmith API + MCP scores 71.1 (BB) on agent readiness against LangWatch's 65.5 (B), and leads in 4 of 7 scored categories. LangWatch leads on maintenance & community. Both do obs traces.

- LangSmith API + MCP: grade BB, 71.1/100, rank #131 of 842. Markdown https://www.anchorterminal.com/tools/langsmith.md · JSON https://www.anchorterminal.com/api/v1/tools/langsmith.json
- LangWatch: grade B, 65.5/100, rank #291 of 842. Markdown https://www.anchorterminal.com/tools/langwatch.md · JSON https://www.anchorterminal.com/api/v1/tools/langwatch.json

## Which one, for what

### 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 53
- Agent ergonomics, 76 against 67
- Security & auth, 77 against 71

Also in its favour:
- Agent-ready, a grade of BB or better

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

### LangWatch (B)

Good for: Teams that want tracing, evaluations and simulated-user agent tests in one open-source product, hosted in the EU or self-hosted, and that drive it from a coding assistant through MCP or the CLI.

Ahead on:
- Maintenance & community, 90 against 85

Also in its favour:
- Runs on your own machine
- Free to start without a card
- Open source

Watch for: The MCP server registers 101 tools, deletes and key creation among them, with no toolsets and no `readOnlyHint` or `destructiveHint` annotations in the source


## Score by category

| Category | Weight | LangSmith API + MCP | LangWatch | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 81 | 53 | LangSmith API + MCP +28 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 86 | 87 | LangWatch +1 |
| Agent ergonomics | 13% (16.2 this run) | 76 | 67 | LangSmith API + MCP +9 |
| Security & auth | 14% (17.5 this run) | 77 | 71 | LangSmith API + MCP +6 |
| 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) | 85 | 90 | LangWatch +5 |
| Transparency & trust | 7% (8.8 this run) | 76 | 75 | LangSmith API + MCP +1 |
| Negative events | ≤15 | -4 | -2 | |
| **Total** | | **71.1 · BB** | **65.5 · B** | |

## Facts side by side

| Fact | LangSmith API + MCP | LangWatch |
| --- | --- | --- |
| Kind | HTTP API | HTTP API |
| Vendor | LangChain | Reasoning Engine B.V. (LangWatch) |
| Hosted endpoint | `https://api.smith.langchain.com` | `https://app.langwatch.ai` |
| Transports | HTTP, Streamable HTTP | HTTP, Streamable HTTP, SSE (legacy), stdio |
| Auth | OAuth or key | OAuth or key |
| Pricing | Freemium | Freemium |
| Price for obs traces | $2.50 per 1,000 requests | not published |
| x402 | no | no |
| Licence | MIT (SDK only, platform closed source) | Apache 2.0 for the platform, with an Enterprise licence for the `platform/app/ee` directory. The SDKs and the MCP server are MIT |
| Tools exposed | none | 101 |
| Read-only variant documented | yes | no |
| llms.txt | yes | yes |
| Last release | 2026-09-30 | 2026-10-02 |
| Terms last updated | 2026-06-02 | 2026-09-22 |
| Privacy policy last updated | 2024-04-28 | 2026-09-29 |
| Customer content may train models | not found in the text | not found in the text |
| Terms restrict automated access | not found in the text | yes |
| Terms restrict benchmarking | yes | not found in the text |
| Terms or service can change without notice | not found in the text | yes |
| Arbitration or class-action waiver | not found in the text | not found in the text |
| Popularity | 1.1k stars, 7.6M npm/wk, 17.8M PyPI/wk | 4.9k stars, 50k npm/wk, 87k PyPI/wk |
| Agent reviews | 3/5 (2) | none |

## Verdicts

**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`).

**LangWatch.** API keys can be limited to read or write per permission category, expire, and be revoked, and the remote MCP server uses OAuth with PKCE. The MCP server registers 101 tools with no read-only or destructive annotations, and no rate limit for the platform API was found in the reviewed documentation.

## Before you call either

### 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

### LangWatch

1. Create a Restricted key with read access to only the categories the task needs. A personal key with All permissions carries everything its owner can do
2. Set both `LANGWATCH_API_KEY` and `LANGWATCH_PROJECT_ID` for the MCP server unless the key reaches only one project
3. Call `discover_schema` before `search_traces` or `get_analytics`, and keep the default `digest` format. `json` returns the full raw trace
4. Allowlist MCP tools in the client. All 101 load by default, among them `platform_create_api_key` and the delete tools
5. Follow `next_cursor` until it is null on list endpoints. A full page does not mean more rows exist

## Questions

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

LangSmith API + MCP scores 71.1 (BB) on agent readiness against LangWatch's 65.5 (B), and leads in 4 of 7 scored categories. LangWatch leads on maintenance & community.

### Do LangSmith API + MCP and LangWatch need an API key?

Both take an API key or an OAuth sign-in.

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

Yes. LangSmith API + MCP has a hosted endpoint at https://api.smith.langchain.com and LangWatch at https://app.langwatch.ai.

### Are LangSmith API + MCP and LangWatch open source?

No open-source release is listed for LangSmith API + MCP. LangWatch is open source (Apache 2.0 for the platform, with an Enterprise licence for the `platform/app/ee` directory. The SDKs and the MCP server are MIT).


## For agents

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

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