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Head to head · Obs traces · October 2026 research run

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.

Braintrust API + MCPBraintrust · HTTP API C61.1/100#433 of 841 W&B WeaveWeights & Biases (CoreWeave) · HTTP API B66.7/100#260 of 841

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

CategoryWeight this runBraintrust API + MCPW&B WeaveEdge
Reliability16%206168W&B Weave +7
Performance10%pendingpendingpendingnot scored in this run
Schema & documentation13%16.28574Braintrust API + MCP +11
Agent ergonomics13%16.26671W&B Weave +5
Security & auth14%17.55863W&B Weave +5
Payments & pricing10%12.54035Braintrust API + MCP +5
Task success10%pendingpendingpendingnot scored in this run
Maintenance & community7%8.88587W&B Weave +2
Transparency & trust7%8.86675W&B Weave +9
Negative events≤15-40
Total61.1 · C66.7 · B

Facts side by side

FactBraintrust API + MCPW&B Weave
KindHTTP APIHTTP API
VendorBraintrustWeights & Biases (CoreWeave)
Hosted endpointhttps://api.braintrust.dev/v1https://trace.wandb.ai
TransportsHTTP, Streamable HTTPHTTP, Streamable HTTP
AuthOAuth or keyAPI key
PricingFreemiumFreemium
x402nono
LicenceApache-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 exposed42none
Read-only variant documentedyesno
llms.txtyesyes
MCP registryio.github.braintrustdata/braintrustnot listed
Last release2026-10-012026-09-25
Terms last updated2026-07-072026-09-30
Privacy policy last updated2023-09-212026-02-24
Customer content may train modelsnot found in the textnot found in the text
Terms restrict automated accessnot found in the textyes
Terms restrict benchmarkingyesyes
Terms or service can change without noticenot found in the textnot found in the text
Arbitration or class-action waiveryesyes
Popularity2M npm/wk, 1.7M PyPI/wk624k npm/wk, 219k PyPI/wk
Agent reviews3/5 (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).

Other comparisons with Braintrust API + MCP or W&B Weave

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