# Prefactor vs W&B Weave

> W&B Weave scores 66.7 (B) on agent readiness against Prefactor's 65.6 (B), and leads in 3 of 7 scored categories. Prefactor leads on reliability, schema & documentation, agent ergonomics and payments & pricing. Both do obs traces. Category scores, facts, verdicts and agent notes…

- Canonical: https://www.anchorterminal.com/compare/prefactor-vs-wandb-weave
- Markdown: https://www.anchorterminal.com/compare/prefactor-vs-wandb-weave.md (~2,550 tokens)
- Slim: https://www.anchorterminal.com/compare/prefactor-vs-wandb-weave.min.md (~730 tokens, same facts, less prose, for token-sensitive contexts)
- JSON: https://www.anchorterminal.com/compare/prefactor-vs-wandb-weave.json (this page as data, same URL with Accept: application/json)
- Site index for agents: https://www.anchorterminal.com/llms.txt (full text: https://www.anchorterminal.com/llms-full.txt)
- API: https://www.anchorterminal.com/api/v1/index.json
- Updated: 2026-10-09

W&B Weave scores 66.7 (B) on agent readiness against Prefactor's 65.6 (B), and leads in 3 of 7 scored categories. Prefactor leads on reliability, schema & documentation, agent ergonomics and payments & pricing. Both do obs traces.

- Prefactor: grade B, 65.6/100, rank #286 of 842. Markdown https://www.anchorterminal.com/tools/prefactor.md · JSON https://www.anchorterminal.com/api/v1/tools/prefactor.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

### Prefactor (B)

Good for: A team that wants an auditable record of agent runs with declared data-risk labels, quality payloads from its own evaluations and a remote stop signal.

Ahead on:
- Reliability, 78 against 68
- Schema & documentation, 80 against 74
- Agent ergonomics, 88 against 71
- Payments & pricing, 40 against 35

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

Watch for: The pricing page lists hold, approve or block and PII detection on every plan, while the docs say a risk threshold blocks nothing and that Prefactor does not detect sensitive data

### 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:
- Security & auth, 63 against 56
- Maintenance & community, 87 against 82
- Transparency & trust, 75 against 42

Also in its favour:
- Open source
- No incidents deducted, where Prefactor loses 3 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 | Prefactor | W&B Weave | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 78 | 68 | Prefactor +10 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 80 | 74 | Prefactor +6 |
| Agent ergonomics | 13% (16.2 this run) | 88 | 71 | Prefactor +17 |
| Security & auth | 14% (17.5 this run) | 56 | 63 | W&B Weave +7 |
| Payments & pricing | 10% (12.5 this run) | 40 | 35 | Prefactor +5 |
| Task success | 10%, pending | pending | pending | not scored in this run |
| Maintenance & community | 7% (8.8 this run) | 82 | 87 | W&B Weave +5 |
| Transparency & trust | 7% (8.8 this run) | 42 | 75 | W&B Weave +33 |
| Negative events | ≤15 | -3 | 0 | |
| **Total** | | **65.6 · B** | **66.7 · B** | |

## Facts side by side

| Fact | Prefactor | W&B Weave |
| --- | --- | --- |
| Kind | HTTP API | HTTP API |
| Vendor | Prefactor Pty Ltd | Weights & Biases (CoreWeave) |
| Hosted endpoint | `https://app.prefactorai.com/api/v1` | `https://trace.wandb.ai` |
| Transports | HTTP | HTTP, Streamable HTTP |
| Auth | API key | API key |
| Pricing | Freemium | Freemium |
| x402 | no | no |
| Licence | Proprietary hosted service. The TypeScript and Python SDKs and the CLI 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 |
| Read-only variant documented | no | no |
| llms.txt | yes | yes |
| Last release | 2026-09-13 | 2026-09-25 |
| Terms last updated | no document linked | 2026-09-30 |
| Privacy policy last updated | couldn't be read | 2026-02-24 |
| Customer content may train models |  | not found in the text |
| Terms restrict automated access |  | yes |
| Terms restrict benchmarking |  | yes |
| Terms or service can change without notice |  | not found in the text |
| Arbitration or class-action waiver |  | yes |
| Popularity | 3 stars, 19 npm/wk, 28 PyPI/wk | 624k npm/wk, 219k PyPI/wk |

## Verdicts

**Prefactor.** The public OpenAPI document lists 157 operations, each accepting an idempotency key, and tokens can be read-only or bound to one agent deployment. The pricing and security pages describe approval, blocking and PII detection that the documentation says the product does not do, and the only published terms cover the website.

**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

### Prefactor

1. Send requests to `https://app.prefactorai.com/api/v1` with `Authorization: Bearer <token>`. The API host is not on the `prefactor.tech` or `prefactor.ai` domains
2. Ask for a deployment-scoped token, or an account token created with `role` set to `read_only`, since the default role is `full_access` with a two-year expiry
3. Pass `redacted: true` on span list and detail queries, because the API returns marked sensitive values unless asked otherwise
4. On 429 wait for `retry_after_ms`. Limits use one-minute windows and the SDKs' default retries ignore the server's hint
5. Treat terminate as a request. Check the control signal on span responses or poll the instance, because Prefactor does not stop the process

### 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, Prefactor or W&B Weave?

W&B Weave scores 66.7 (B) on agent readiness against Prefactor's 65.6 (B), and leads in 3 of 7 scored categories. Prefactor leads on reliability, schema & documentation, agent ergonomics and payments & pricing.

### Do Prefactor and W&B Weave need an API key?

Both need an API key.

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

Yes. Prefactor has a hosted endpoint at https://app.prefactorai.com/api/v1 and W&B Weave at https://trace.wandb.ai.

### Are Prefactor and W&B Weave open source?

No open-source release is listed for Prefactor. 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/prefactor-vs-wandb-weave.json, and with the fewest tokens: https://www.anchorterminal.com/compare/prefactor-vs-wandb-weave.min.md
- Over MCP at https://www.anchorterminal.com/mcp (no key): `compare_tools {"a": "prefactor", "b": "wandb-weave"}`. From a terminal: `anchor compare prefactor wandb-weave`
- Each listing in full: https://www.anchorterminal.com/api/v1/tools/prefactor.json and https://www.anchorterminal.com/api/v1/tools/wandb-weave.json

## Other comparisons with Prefactor or W&B Weave

- [Arize Phoenix vs Prefactor](https://www.anchorterminal.com/compare/arize-phoenix-vs-prefactor.md)
- [Arize Phoenix vs W&B Weave](https://www.anchorterminal.com/compare/arize-phoenix-vs-wandb-weave.md)
- [Baserun vs Prefactor](https://www.anchorterminal.com/compare/baserun-vs-prefactor.md)
- [Baserun vs W&B Weave](https://www.anchorterminal.com/compare/baserun-vs-wandb-weave.md)
- [Braintrust API + MCP vs Prefactor](https://www.anchorterminal.com/compare/braintrust-vs-prefactor.md)
- [Braintrust API + MCP vs W&B Weave](https://www.anchorterminal.com/compare/braintrust-vs-wandb-weave.md)
- [Galileo API + MCP vs Prefactor](https://www.anchorterminal.com/compare/galileo-vs-prefactor.md)
- [Galileo API + MCP vs W&B Weave](https://www.anchorterminal.com/compare/galileo-vs-wandb-weave.md)
- [Helicone AI Gateway + MCP vs Prefactor](https://www.anchorterminal.com/compare/helicone-vs-prefactor.md)
- [Helicone AI Gateway + MCP vs W&B Weave](https://www.anchorterminal.com/compare/helicone-vs-wandb-weave.md)
- [HoneyHive vs Prefactor](https://www.anchorterminal.com/compare/honeyhive-vs-prefactor.md)
- [HoneyHive vs W&B Weave](https://www.anchorterminal.com/compare/honeyhive-vs-wandb-weave.md)
- [Laminar API + MCP vs Prefactor](https://www.anchorterminal.com/compare/laminar-vs-prefactor.md)
- [Laminar API + MCP vs W&B Weave](https://www.anchorterminal.com/compare/laminar-vs-wandb-weave.md)
- [Langfuse API + MCP vs Prefactor](https://www.anchorterminal.com/compare/langfuse-vs-prefactor.md)
- [Langfuse API + MCP vs W&B Weave](https://www.anchorterminal.com/compare/langfuse-vs-wandb-weave.md)
- [LangSmith API + MCP vs Prefactor](https://www.anchorterminal.com/compare/langsmith-vs-prefactor.md)
- [LangSmith API + MCP vs W&B Weave](https://www.anchorterminal.com/compare/langsmith-vs-wandb-weave.md)
- [LangWatch vs Prefactor](https://www.anchorterminal.com/compare/langwatch-vs-prefactor.md)
- [LangWatch vs W&B Weave](https://www.anchorterminal.com/compare/langwatch-vs-wandb-weave.md)
- [Prefactor vs Respan API + MCP](https://www.anchorterminal.com/compare/prefactor-vs-respan.md)
- [Respan API + MCP vs W&B Weave](https://www.anchorterminal.com/compare/respan-vs-wandb-weave.md)