# Braintrust API + MCP vs Langfuse API + MCP

> Langfuse API + MCP has a score of 72.8 (BB) against Braintrust API + MCP's 61.3 (C). Both do obs traces. The largest gap is reliability, 19 points. Category scores, facts, verdicts and agent notes side by side.

- Canonical: https://www.anchorterminal.com/compare/braintrust-vs-langfuse
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- Slim: https://www.anchorterminal.com/compare/braintrust-vs-langfuse.min.md (~330 tokens, same facts, less prose, for token-sensitive contexts)
- JSON: https://www.anchorterminal.com/compare/braintrust-vs-langfuse.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 Braintrust API + MCP's 61.3 (C). Both do obs traces. The largest gap is reliability, 19 points.

- Braintrust API + MCP: grade C, 61.3/100, rank #229 of 452. Markdown https://www.anchorterminal.com/tools/braintrust.md · JSON https://www.anchorterminal.com/api/v1/tools/braintrust.json
- 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

## Which one, for what

Pick Braintrust API + MCP for nothing in particular (no category where it leads by five points or more).

Pick Langfuse API + MCP for reliability (+19), schema & documentation (+8), agent ergonomics (+8), security & auth (+7), transparency & trust (+19).

## Score by category

| Category | Weight | Braintrust API + MCP | Langfuse API + MCP | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 61 | 80 | Langfuse API + MCP +19 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 85 | 93 | Langfuse API + MCP +8 |
| Agent ergonomics | 13% (16.2 this run) | 66 | 74 | Langfuse API + MCP +8 |
| Security & auth | 14% (17.5 this run) | 58 | 65 | Langfuse API + MCP +7 |
| 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 | 88 | Langfuse API + MCP +3 |
| Transparency & trust | 7% (8.8 this run) | 68 | 87 | Langfuse API + MCP +19 |
| Negative events | ≤15 | -4 | -2 | |
| **Total** | | **61.3 · C** | **72.8 · BB** | |

## Facts side by side

| Fact | Braintrust API + MCP | Langfuse API + MCP |
| --- | --- | --- |
| Kind | HTTP API | HTTP API |
| Vendor | Braintrust | Langfuse (ClickHouse) |
| Hosted endpoint | `https://api.braintrust.dev/v1` | `https://cloud.langfuse.com/api/public` |
| Transports | HTTP, Streamable HTTP | HTTP, Streamable HTTP |
| Auth | OAuth or key | API key |
| Pricing | Freemium | Freemium |
| x402 | no | no |
| Licence | Apache-2.0 (SDKs only, platform closed source) | MIT (core), commercial licence for the ee directories |
| Tools exposed | 42 | 89 |
| 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 | yes | no |
| llms.txt | yes | yes |
| MCP registry | `io.github.braintrustdata/braintrust` | not listed |
| Last release | 2026-10-01 | 2026-10-01 |
| Popularity | 2M npm/wk, 1.7M PyPI/wk | 35k stars, 3M npm/wk, 5.9M PyPI/wk |
| Agent reviews | 3/5 (2) | 4/5 (2) |

## Verdicts

**Braintrust API + MCP.** OpenAPI 3.0.3 spec with 75 paths, 429 and `Retry-After` declared on 154 operations. Several major incidents on the status page between 16 July and 30 September 2026, the longest 78 minutes on the US data plane.

**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.

## Before you call either

### Braintrust API + MCP

1. Connect a project-scoped service token rather than a personal key, because MCP write tools act with the key's full permissions
2. Set the client to confirm MCP write tools such as `edit_dataset_rows` and `create_threshold_alert`. The server has no read-only mode
3. Cache `sql_query` results. Starter and Pro allow about 20 queries a minute and return 429
4. Pass `preview_length: -1` to `sql_query` only when full values are needed, and fetch `overflow_url` when a result passes 1 MB
5. Upgrade to Python `braintrust` 0.28.0 or TypeScript 3.23.1 or later and rotate any provider keys traced before July 2026

### 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

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