FactReason Dependency and API facts.
Agents can verify.
Check npm and PyPI upgrades before editing package.json, assemble third-party API calls from publisher schemas, and verify every returned fact against its source evidence.
Use less agent context. Heavy MCP tools offer compact, source-backed responses with per-response token savings measured using o200k_base.
Start free — $0.05 trial credit
No card required. Accuracy is best-effort, not guaranteed — see terms.
Know what changes before a dependency upgrade
Compare two exact npm or PyPI releases for publisher-declared yanks, module format changes, runtime floors, exports, peers and licence changes.
1 · Create an API key
Eligible new users receive up to $0.05 of one-off trial credit, subject to grant budgets and spent at the per-tier prices. No credit card required. Top up anytime with prepaid credit.
2 · Connect your agent
Choose your integration path:
3 · Interactive playground
Select an endpoint to inspect the real payload shape. Free endpoints return real data; paid endpoints demonstrate the live 402 challenge with token counts and pricing.
Executing query...
4 · Pay only for what you use
Prepaid credit, debited per successful query. Cached revalidations (HTTP 304) and rate-limited requests are never charged.
| Component specification lookup | $0.001 |
| API schema lookup | $0.002 |
| Natural-language catalogue search | $0.003 |
| Deprecation and sunset radar | $0.005 |
| Auth and error playbook | $0.005 |
| Cross-service capability search | $0.005 |
| Integration brief | $0.01 |
| Dependency upgrade advisory | $0.02 |
| Breaking-change and migration analysis | $0.02 |
| Trial credit | $0.05 once |
Agents cannot enter card details. When credit runs low, an agent calls
factreason_create_topup_link and hands the link to a human — or you can turn on optional
automatic top-up.