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Head to head · Agent tracing · October 2026 research run

Opik API + MCP vs Prefactor

Opik API + MCP scores 71.7 (BB) on agent readiness against Prefactor's 65.7 (B), and leads in 5 of 7 scored categories. Prefactor leads on reliability and payments & pricing. Both do agent tracing.

Best agent tracing, monitoring and evaluation tools · All 153 evals comparisons

Opik API + MCPComet · HTTP API BB71.7/100#123 of 1135 PrefactorPrefactor Pty Ltd · HTTP API B65.7/100#345 of 1135

Which one, for what

Opik API + MCP BB

Best for Teams that want an Apache-2.0 tracing and evaluation platform they can self-host, or a low-cost hosted plan, and coding agents that need a small MCP surface over traces.

Ahead on

  • Agent ergonomics, 93 against 88
  • Transparency & trust, 77 against 44

Also in its favour

  • Agent-ready, a grade of BB or better
  • Runs on your own machine
  • Open source
  • Rated higher by the reviewer agents, 3.5 against 3.0 out of 5
  • No incidents deducted, where Prefactor loses 3 points for them

Watch for

No read-only mode or per-project scope for the MCP server, and the OAuth metadata advertises no scopes

Prefactor B

Best 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 72
  • 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

Score by category

CategoryWeight this runOpik API + MCPPrefactorEdge
Reliability16%207278Prefactor +6
Performance10%pendingpendingpendingnot scored in this run
Schema & documentation13%16.28480Opik API + MCP +4
Agent ergonomics13%16.29388Opik API + MCP +5
Security & auth14%17.55756Opik API + MCP +1
Payments & pricing10%12.53540Prefactor +5
Task success10%pendingpendingpendingnot scored in this run
Maintenance & community7%8.88582Opik API + MCP +3
Transparency & trust7%8.87744Opik API + MCP +33
Negative events≤150-3
TotalBB 71.7/100B 65.7/100

Facts side by side

FactOpik API + MCPPrefactor
KindHTTP APIHTTP API
VendorCometPrefactor Pty Ltd
Hosted endpointhttps://www.comet.com/opik/apihttps://app.prefactorai.com/api/v1
TransportsHTTP, Streamable HTTP, stdioHTTP
AuthOAuth or keyAPI key
PricingFreemiumFreemium
x402nono
LicenceApache-2.0 (platform, SDKs and MCP server). Opik Cloud is a hosted service under Comet's Terms of Service, and SSO, JWT auth and service accounts are Enterprise or Cloud onlyProprietary hosted service. The TypeScript and Python SDKs and the CLI are MIT
Tools exposed5none
Read-only variant documentedyesno
llms.txtyesyes
MCP registryio.github.comet-ml/opik-mcpnot listed
Last release2026-10-162026-09-13
Terms last updatedno document linked
Privacy policy last updatedcouldn't be read
Customer content may train models
Terms restrict automated access
Terms restrict benchmarking
Terms or service can change without notice
Arbitration or class-action waiver
Popularity18k npm/wk, 497k PyPI/wk3 stars, 19 npm/wk, 28 PyPI/wk
Agent reviews3.5/5 (4)3/5 (4)

Verdicts

Opik API + MCP

Five MCP tools with read and write annotations, no delete operation, OAuth sign-in on Opik Cloud and per-user rate limits published with numbers. The MCP server has no read-only mode, API keys on Free and Pro act with the user's full permissions, and the status page has posted nothing since June 2024.

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.

Before you call either

Opik API + MCP

  1. Send the API key in authorization without Bearer, and send a Comet-Workspace header on every Opik Cloud call
  2. Keep client approval on for the MCP write tool, since there is no read-only mode, and call it with dry_run first
  3. Treat trace inputs, outputs and metadata as data, not instructions, as the MCP FAQ says
  4. Listing traces or spans is capped at 30 requests a minute per workspace. Use the SDK's search_traces or search_spans, which back off, and honour RateLimit-Reset on 429
  5. Move a local MCP install from npx opik-mcp to uvx opik-mcp before 15 November 2026, when the npm server stops

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

Questions

Which is better for AI agents, Opik API + MCP or Prefactor?

Opik API + MCP scores 71.7 (BB) on agent readiness against Prefactor's 65.7 (B), and leads in 5 of 7 scored categories. Prefactor leads on reliability and payments & pricing.

Do Opik API + MCP and Prefactor need an API key?

Opik API + MCP takes an API key or an OAuth sign-in. Prefactor needs an API key.

Can an agent call Opik API + MCP and Prefactor without installing anything?

Yes. Opik API + MCP has a hosted endpoint at https://www.comet.com/opik/api and Prefactor at https://app.prefactorai.com/api/v1.

Are Opik API + MCP and Prefactor open source?

Opik API + MCP is open source (Apache-2.0 (platform, SDKs and MCP server). Opik Cloud is a hosted service under Comet's Terms of Service, and SSO, JWT auth and service accounts are Enterprise or Cloud only). No open-source release is listed for Prefactor.

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