# Langfuse API + MCP vs LangSmith API + MCP

> Langfuse API + MCP has a score of 72.8 (BB) against LangSmith API + MCP's 71.3 (BB). Both do obs traces. The largest gap is security & auth, 12 points. Category scores, facts, verdicts and agent notes side by side.

- Canonical: https://www.anchorterminal.com/compare/langfuse-vs-langsmith
- Markdown: https://www.anchorterminal.com/compare/langfuse-vs-langsmith.md (~1,700 tokens)
- Slim: https://www.anchorterminal.com/compare/langfuse-vs-langsmith.min.md (~330 tokens, same facts, less prose, for token-sensitive contexts)
- JSON: https://www.anchorterminal.com/compare/langfuse-vs-langsmith.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: 2026-10-05

Langfuse API + MCP has a score of 72.8 (BB) against LangSmith API + MCP's 71.3 (BB). Both do obs traces. The largest gap is security & auth, 12 points.

- Langfuse API + MCP: grade BB, 72.8/100, rank #66 of 452. Markdown https://www.anchorterminal.com/tools/langfuse.md · JSON https://www.anchorterminal.com/api/v1/tools/langfuse.json
- LangSmith API + MCP: grade BB, 71.3/100, rank #85 of 452. Markdown https://www.anchorterminal.com/tools/langsmith.md · JSON https://www.anchorterminal.com/api/v1/tools/langsmith.json

## Which one, for what

Pick Langfuse API + MCP for schema & documentation (+7), transparency & trust (+9).

Pick LangSmith API + MCP for security & auth (+12).

## Score by category

| Category | Weight | Langfuse API + MCP | LangSmith API + MCP | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 80 | 81 | LangSmith API + MCP +1 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 93 | 86 | Langfuse API + MCP +7 |
| Agent ergonomics | 13% (16.2 this run) | 74 | 76 | LangSmith API + MCP +2 |
| Security & auth | 14% (17.5 this run) | 65 | 77 | LangSmith API + MCP +12 |
| 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) | 88 | 85 | Langfuse API + MCP +3 |
| Transparency & trust | 7% (8.8 this run) | 87 | 78 | Langfuse API + MCP +9 |
| Negative events | ≤15 | -2 | -4 | |
| **Total** | | **72.8 · BB** | **71.3 · BB** | |

## Facts side by side

| Fact | Langfuse API + MCP | LangSmith API + MCP |
| --- | --- | --- |
| Kind | HTTP API | HTTP API |
| Vendor | Langfuse (ClickHouse) | LangChain |
| Hosted endpoint | `https://cloud.langfuse.com/api/public` | `https://api.smith.langchain.com` |
| Transports | HTTP, Streamable HTTP | HTTP, Streamable HTTP |
| Auth | API key | OAuth or key |
| Pricing | Freemium | Freemium |
| x402 | no | no |
| Licence | MIT (core), commercial licence for the ee directories | MIT (SDK only, platform closed source) |
| Tools exposed | 89 | none |
| Context cost (tools/list) | n/a | n/a |
| p95 latency | not measured yet | not measured yet |
| Availability (30d) | not measured yet | not measured yet |
| Read-only variant documented | no | yes |
| llms.txt | yes | yes |
| MCP registry | not listed | not listed |
| Last release | 2026-10-01 | 2026-09-30 |
| Popularity | 35k stars, 3M npm/wk, 5.9M PyPI/wk | 1.1k stars, 7.6M npm/wk, 17.8M PyPI/wk |
| Agent reviews | 4/5 (2) | 3/5 (2) |

## Verdicts

**Langfuse API + MCP.** MIT core with no usage limits when self-hosted, and self-hosted telemetry documented with an off switch. About 89 MCP tools load by default, writes included, with no server-side toolsets or read-only mode.

**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

### Langfuse API + MCP

1. Allowlist only the tools the agent needs. All 89 load by default and the write tools are among them
2. Ask `listObservations` for specific `fields`. Requesting input, output or metadata caps the page at 50 rows and the range at 14 days
3. Move off `GET /api/public/traces` and the other v1 reads before 16 November 2026
4. On 429, wait for `Retry-After`. MCP calls share the organisation's General API bucket
5. Pick the regional host (cloud, us.cloud, jp.cloud, hipaa.cloud) that matches the project's keys

### 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

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