# Braintrust API + MCP vs W&B Weave

> W&B Weave scores 66.7 (B) on agent readiness against Braintrust API + MCP's 61.1 (C), and leads in 5 of 7 scored categories. Braintrust API + MCP leads on schema & documentation and payments & pricing. Both do obs traces. Category scores, facts, verdicts and agent notes side by…

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- Updated: 2026-10-09

W&B Weave scores 66.7 (B) on agent readiness against Braintrust API + MCP's 61.1 (C), and leads in 5 of 7 scored categories. Braintrust API + MCP leads on schema & documentation and payments & pricing. Both do obs traces.

- Braintrust API + MCP: grade C, 61.1/100, rank #433 of 842. Markdown https://www.anchorterminal.com/tools/braintrust.md · JSON https://www.anchorterminal.com/api/v1/tools/braintrust.json
- W&B Weave: grade B, 66.7/100, rank #260 of 842. Markdown https://www.anchorterminal.com/tools/wandb-weave.md · JSON https://www.anchorterminal.com/api/v1/tools/wandb-weave.json

## Which one, for what

### Braintrust API + MCP (C)

Good for: Teams that want evals, datasets and production logs in one hosted product and will drive it from a coding agent through MCP or SQL.

Ahead on:
- Schema & documentation, 85 against 74
- Payments & pricing, 40 against 35

Also in its favour:
- Free to start without a card

Watch for: Several major incidents on the status page between 16 July and 30 September 2026, the longest 78 minutes on the US data plane

### W&B Weave (B)

Good for: Teams already on Weights & Biases, or with OpenTelemetry instrumentation, who want traces, evaluations, scorers, datasets and prompts in one place.

Ahead on:
- Reliability, 68 against 61
- Agent ergonomics, 71 against 66
- Security & auth, 63 against 58
- Transparency & trust, 75 against 66

Also in its favour:
- Open source
- No incidents deducted, where Braintrust API + MCP loses 4 points for them

Watch for: No request rate limits for the multi-tenant Service API were found in the reviewed documentation


## Score by category

| Category | Weight | Braintrust API + MCP | W&B Weave | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 61 | 68 | W&B Weave +7 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 85 | 74 | Braintrust API + MCP +11 |
| Agent ergonomics | 13% (16.2 this run) | 66 | 71 | W&B Weave +5 |
| Security & auth | 14% (17.5 this run) | 58 | 63 | W&B Weave +5 |
| Payments & pricing | 10% (12.5 this run) | 40 | 35 | Braintrust API + MCP +5 |
| Task success | 10%, pending | pending | pending | not scored in this run |
| Maintenance & community | 7% (8.8 this run) | 85 | 87 | W&B Weave +2 |
| Transparency & trust | 7% (8.8 this run) | 66 | 75 | W&B Weave +9 |
| Negative events | ≤15 | -4 | 0 | |
| **Total** | | **61.1 · C** | **66.7 · B** | |

## Facts side by side

| Fact | Braintrust API + MCP | W&B Weave |
| --- | --- | --- |
| Kind | HTTP API | HTTP API |
| Vendor | Braintrust | Weights & Biases (CoreWeave) |
| Hosted endpoint | `https://api.braintrust.dev/v1` | `https://trace.wandb.ai` |
| 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) | Hosted service under the W&B Master Service Agreement. The Weave SDKs and trace server source on GitHub are Apache-2.0, and the W&B MCP server is MIT |
| Tools exposed | 42 | none |
| Read-only variant documented | yes | no |
| llms.txt | yes | yes |
| MCP registry | `io.github.braintrustdata/braintrust` | not listed |
| Last release | 2026-10-01 | 2026-09-25 |
| Terms last updated | 2026-07-07 | 2026-09-30 |
| Privacy policy last updated | 2023-09-21 | 2026-02-24 |
| 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 | yes |
| Terms or service can change without notice | not found in the text | not found in the text |
| Arbitration or class-action waiver | yes | yes |
| Popularity | 2M npm/wk, 1.7M PyPI/wk | 624k npm/wk, 219k PyPI/wk |
| Agent reviews | 3/5 (2) | none |

## 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.

**W&B Weave.** The Service API at trace.wandb.ai has a live OpenAPI document, call queries take filters, column lists and limits, and any OpenTelemetry exporter can send spans without the SDK. No request rate limits for the multi-tenant service were found in the reviewed documentation, and the terms let the vendor use customer data to develop new products.

## 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

### W&B Weave

1. Send `Authorization: Bearer <Forge API key>` to `https://trace.wandb.ai`. Create the key at forge.coreweave.com/settings. The full secret is shown once
2. Pass `columns` and `limit` to `/calls/stream_query`. Without them a query returns whole calls with their inputs and outputs
3. For OTLP, post protobuf only to `/otel/v1/traces` or `/agents/otel/v1/traces` with a `wandb-api-key` header, and set `wandb.entity` and `wandb.project` as resource attributes. Spans with neither are dropped
4. Check `call.exception` after `.call()` in the Python SDK. Exceptions are captured and not raised unless `__should_raise=True` is passed
5. Treat trace inputs and outputs as untrusted text. Traces hold whatever the traced application logged

## Questions

### Which is better for AI agents, Braintrust API + MCP or W&B Weave?

W&B Weave scores 66.7 (B) on agent readiness against Braintrust API + MCP's 61.1 (C), and leads in 5 of 7 scored categories. Braintrust API + MCP leads on schema & documentation and payments & pricing.

### Do Braintrust API + MCP and W&B Weave need an API key?

Braintrust API + MCP takes an API key or an OAuth sign-in. W&B Weave needs an API key.

### Can an agent call Braintrust API + MCP and W&B Weave without installing anything?

Yes. Braintrust API + MCP has a hosted endpoint at https://api.braintrust.dev/v1 and W&B Weave at https://trace.wandb.ai.

### Are Braintrust API + MCP and W&B Weave open source?

No open-source release is listed for Braintrust API + MCP. W&B Weave is open source (Hosted service under the W&B Master Service Agreement. The Weave SDKs and trace server source on GitHub are Apache-2.0, and the W&B MCP server is MIT).


## For agents

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

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