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Head to head · Obs traces · October 2026 research run

LangWatch vs W&B Weave

W&B Weave scores 66.7 (B) on agent readiness against LangWatch's 65.5 (B), and leads in 2 of 7 scored categories. LangWatch leads on schema & documentation, security & auth and payments & pricing. Both do obs traces.

LangWatchReasoning Engine B.V. (LangWatch) · HTTP API B65.5/100#291 of 841 W&B WeaveWeights & Biases (CoreWeave) · HTTP API B66.7/100#260 of 841

Which one, for what

LangWatch B

Good for Teams that want tracing, evaluations and simulated-user agent tests in one open-source product, hosted in the EU or self-hosted, and that drive it from a coding assistant through MCP or the CLI.

Ahead on

  • Schema & documentation, 87 against 74
  • Security & auth, 71 against 63
  • Payments & pricing, 40 against 35

Also in its favour

  • Runs on your own machine
  • Free to start without a card

Watch for

The MCP server registers 101 tools, deletes and key creation among them, with no toolsets and no readOnlyHint or destructiveHint annotations in the source

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 53

Watch for

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

Score by category

CategoryWeight this runLangWatchW&B WeaveEdge
Reliability16%205368W&B Weave +15
Performance10%pendingpendingpendingnot scored in this run
Schema & documentation13%16.28774LangWatch +13
Agent ergonomics13%16.26771W&B Weave +4
Security & auth14%17.57163LangWatch +8
Payments & pricing10%12.54035LangWatch +5
Task success10%pendingpendingpendingnot scored in this run
Maintenance & community7%8.89087LangWatch +3
Transparency & trust7%8.87575even
Negative events≤15-20
Total65.5 · B66.7 · B

Facts side by side

FactLangWatchW&B Weave
KindHTTP APIHTTP API
VendorReasoning Engine B.V. (LangWatch)Weights & Biases (CoreWeave)
Hosted endpointhttps://app.langwatch.aihttps://trace.wandb.ai
TransportsHTTP, Streamable HTTP, SSE (legacy), stdioHTTP, Streamable HTTP
AuthOAuth or keyAPI key
PricingFreemiumFreemium
x402nono
LicenceApache 2.0 for the platform, with an Enterprise licence for the platform/app/ee directory. The SDKs and the MCP server are MITHosted 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 exposed101none
Read-only variant documentednono
llms.txtyesyes
Last release2026-10-022026-09-25
Terms last updated2026-09-222026-09-30
Privacy policy last updated2026-09-292026-02-24
Customer content may train modelsnot found in the textnot found in the text
Terms restrict automated accessyesyes
Terms restrict benchmarkingnot found in the textyes
Terms or service can change without noticeyesnot found in the text
Arbitration or class-action waivernot found in the textyes
Popularity4.9k stars, 50k npm/wk, 87k PyPI/wk624k npm/wk, 219k PyPI/wk

Verdicts

LangWatch

API keys can be limited to read or write per permission category, expire, and be revoked, and the remote MCP server uses OAuth with PKCE. The MCP server registers 101 tools with no read-only or destructive annotations, and no rate limit for the platform API was found in the reviewed documentation.

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

LangWatch

  1. Create a Restricted key with read access to only the categories the task needs. A personal key with All permissions carries everything its owner can do
  2. Set both LANGWATCH_API_KEY and LANGWATCH_PROJECT_ID for the MCP server unless the key reaches only one project
  3. Call discover_schema before search_traces or get_analytics, and keep the default digest format. json returns the full raw trace
  4. Allowlist MCP tools in the client. All 101 load by default, among them platform_create_api_key and the delete tools
  5. Follow next_cursor until it is null on list endpoints. A full page does not mean more rows exist

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, LangWatch or W&B Weave?

W&B Weave scores 66.7 (B) on agent readiness against LangWatch's 65.5 (B), and leads in 2 of 7 scored categories. LangWatch leads on schema & documentation, security & auth and payments & pricing.

Do LangWatch and W&B Weave need an API key?

LangWatch takes an API key or an OAuth sign-in. W&B Weave needs an API key.

Can an agent call LangWatch and W&B Weave without installing anything?

Yes. LangWatch has a hosted endpoint at https://app.langwatch.ai and W&B Weave at https://trace.wandb.ai.

Are LangWatch and W&B Weave open source?

Yes. LangWatch is open source (Apache 2.0 for the platform, with an Enterprise licence for the `platform/app/ee` directory. The SDKs and the MCP server are MIT). 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 LangWatch or W&B Weave

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