# 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. Category scores, facts, verdicts and agent notes side by side.

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- API: https://www.anchorterminal.com/api/v1/index.json
- Updated: 2026-10-09

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.

- LangWatch: grade B, 65.5/100, rank #291 of 842. Markdown https://www.anchorterminal.com/tools/langwatch.md · JSON https://www.anchorterminal.com/api/v1/tools/langwatch.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

### 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

| Category | Weight | LangWatch | W&B Weave | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 53 | 68 | W&B Weave +15 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 87 | 74 | LangWatch +13 |
| Agent ergonomics | 13% (16.2 this run) | 67 | 71 | W&B Weave +4 |
| Security & auth | 14% (17.5 this run) | 71 | 63 | LangWatch +8 |
| Payments & pricing | 10% (12.5 this run) | 40 | 35 | LangWatch +5 |
| Task success | 10%, pending | pending | pending | not scored in this run |
| Maintenance & community | 7% (8.8 this run) | 90 | 87 | LangWatch +3 |
| Transparency & trust | 7% (8.8 this run) | 75 | 75 | even |
| Negative events | ≤15 | -2 | 0 | |
| **Total** | | **65.5 · B** | **66.7 · B** | |

## Facts side by side

| Fact | LangWatch | W&B Weave |
| --- | --- | --- |
| Kind | HTTP API | HTTP API |
| Vendor | Reasoning Engine B.V. (LangWatch) | Weights & Biases (CoreWeave) |
| Hosted endpoint | `https://app.langwatch.ai` | `https://trace.wandb.ai` |
| Transports | HTTP, Streamable HTTP, SSE (legacy), stdio | HTTP, Streamable HTTP |
| Auth | OAuth or key | API key |
| Pricing | Freemium | Freemium |
| x402 | no | no |
| Licence | Apache 2.0 for the platform, with an Enterprise licence for the `platform/app/ee` directory. The SDKs and the MCP server are MIT | 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 | 101 | none |
| Read-only variant documented | no | no |
| llms.txt | yes | yes |
| Last release | 2026-10-02 | 2026-09-25 |
| Terms last updated | 2026-09-22 | 2026-09-30 |
| Privacy policy last updated | 2026-09-29 | 2026-02-24 |
| Customer content may train models | not found in the text | not found in the text |
| Terms restrict automated access | yes | yes |
| Terms restrict benchmarking | not found in the text | yes |
| Terms or service can change without notice | yes | not found in the text |
| Arbitration or class-action waiver | not found in the text | yes |
| Popularity | 4.9k stars, 50k npm/wk, 87k PyPI/wk | 624k 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).


## For agents

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

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