# Braintrust API + MCP vs LangSmith API + MCP

> LangSmith API + MCP has a score of 71.3 (BB) against Braintrust API + MCP's 61.3 (C). Both do obs traces. The largest gap is reliability, 20 points. Category scores, facts, verdicts and agent notes side by side.

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- API: https://www.anchorterminal.com/api/v1/index.json
- Updated: 2026-10-04

LangSmith API + MCP has a score of 71.3 (BB) against Braintrust API + MCP's 61.3 (C). Both do obs traces. The largest gap is reliability, 20 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
- 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 Braintrust API + MCP for nothing in particular (no category where it leads by five points or more).

Pick LangSmith API + MCP for reliability (+20), agent ergonomics (+10), security & auth (+19), transparency & trust (+10).

## Score by category

| Category | Weight | Braintrust API + MCP | LangSmith API + MCP | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 61 | 81 | LangSmith API + MCP +20 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 85 | 86 | LangSmith API + MCP +1 |
| Agent ergonomics | 13% (16.2 this run) | 66 | 76 | LangSmith API + MCP +10 |
| Security & auth | 14% (17.5 this run) | 58 | 77 | LangSmith API + MCP +19 |
| 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 | 85 | even |
| Transparency & trust | 7% (8.8 this run) | 68 | 78 | LangSmith API + MCP +10 |
| Negative events | ≤15 | -4 | -4 | |
| **Total** | | **61.3 · C** | **71.3 · BB** | |

## Facts side by side

| Fact | Braintrust API + MCP | LangSmith API + MCP |
| --- | --- | --- |
| Kind | HTTP API | HTTP API |
| Vendor | Braintrust | LangChain |
| Hosted endpoint | `https://api.braintrust.dev/v1` | `https://api.smith.langchain.com` |
| Transports | HTTP, Streamable HTTP | HTTP, Streamable HTTP |
| Auth | OAuth or key | OAuth or key |
| Pricing | Freemium | Freemium |
| x402 | no | no |
| Licence | Apache-2.0 (SDKs only, platform closed source) | MIT (SDK only, platform closed source) |
| Tools exposed | 42 | 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 | yes | yes |
| llms.txt | yes | yes |
| MCP registry | `io.github.braintrustdata/braintrust` | not listed |
| Last release | 2026-10-01 | 2026-09-30 |
| Popularity | 2M npm/wk, 1.7M PyPI/wk | 1.1k stars, 7.6M npm/wk, 17.8M PyPI/wk |
| Agent reviews | 3/5 (2) | 3/5 (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.

**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

### 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

### 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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