factreason

<div align="center"> <img src="./logo.svg" width="96" height="96" alt="FactReason Logo" /> <h1>FactReason</h1> <p><strong>Reference data agents need before they write code.</strong></p> <p>Dependency upgrade advisories for npm and PyPI, developer API schemas across 1,097 services, and electronic component specifications — over MCP, Ed25519-signed, with evidence attached.</p> <p><code>https://factreason.com/mcp</code> · <a href="https://factreason.com/llms.txt">Agent Docs</a> · <a href="https://factreason.com">factreason.com</a></p> </div>

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Stop an agent shipping a broken dependency upgrade

Your agent wants to bump chalk from 4.1.2 to 5.0.0. Before it edits package.json, it asks what breaks:

GET /api/v1/packages/npm/chalk/advisory?from=4.1.2&to=5.0.0
Authorization: Bearer <key>

{
  "found": true,
  "packageName": "chalk",
  "fromVersion": "4.1.2",
  "toVersion": "5.0.0",
  "breakingCount": 2,
  "advisories": [
    {
      "severity": "breaking",
      "changeType": "MODULE_FORMAT_CHANGED",
      "description": "chalk 5.0.0 changed module format from \"commonjs (undeclared)\" to \"module\". CommonJS require() of this package will now fail.",
      "evidenceField": "type",
      "evidenceBefore": null,
      "evidenceAfter": "module",
      "migrationHint": "Convert the call site to import(), or pin to the last CommonJS release."
    },
    {
      "severity": "breaking",
      "changeType": "RUNTIME_REQUIREMENT_RAISED",
      "description": "chalk 5.0.0 raised its runtime requirement from \">=10\" to \"^12.17.0 || ^14.13 || >=16.0.0\". Older runtimes are no longer supported.",
      "evidenceField": "engines.node",
      "evidenceBefore": ">=10",
      "evidenceAfter": "^12.17.0 || ^14.13 || >=16.0.0",
      "migrationHint": "Confirm the deployment runtime satisfies the new floor before upgrading."
    }
  ]
}

Via MCP, the same question is one tool call:

{
  "name": "factreason_package_upgrade_advisory",
  "arguments": { "registry": "npm", "name": "chalk", "from": "4.1.2", "to": "5.0.0" }
}

Every finding carries evidenceField, evidenceBefore and evidenceAfter — the exact registry metadata field and its values either side of the change. An agent can verify the claim against npm or PyPI directly rather than taking our word for it.

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Connect

Streamable HTTP. No install, no package to pull.

{
  "mcpServers": {
    "factreason": {
      "type": "http",
      "url": "https://factreason.com/mcp"
    }
  }
}

Manifest: /.well-known/mcp.json

The container/stdio bridge accepts an optional FACTREASON_API_KEY environment variable and forwards it as a Bearer credential to the same live endpoint. Tool discovery works without a key; metered lookups return HTTP 402 when neither a key nor a valid x402 payment is supplied.

Get a key — no signup, no card:

curl -X POST https://factreason.com/api/v1/keys/create \
  -H 'Content-Type: application/json' \
  -d '{"email":"you@example.com"}'

---

Tools

Tool	What it answers
factreason_package_upgrade_advisory	What breaks between two published npm/PyPI versions
factreason_api_schema	Exact request/response shape of an API endpoint at a version
factreason_integration_brief	Everything needed to write one working call to an API
factreason_discover_api	Which of 1,097 services can do X
factreason_deprecation_scan	Which endpoints are deprecated, sunset dates, replacements
factreason_auth_playbook	Auth schemes, scopes, rate-limit headers, error-code table
factreason_component_spec	Electronics component pinouts, voltages, packages
factreason_subscribe_spec_changes	Webhook or polling callback when a spec changes
factreason_create_topup_link	Stripe checkout link when credit runs out

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Proof-of-Fact Signatures

Every response is signed by our Ed25519 private key:

• X-FactReason-Signature: Ed25519 signature of the raw response payload
• X-FactReason-Key-Id: Stable signing key identifier
• X-FactReason-Signature-Alg: ed25519

Public keys are published and rotated via JWKS at https://factreason.com/.well-known/jwks.json.

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Licence & Contact

MIT. Attribution requirement for APIs.guru source data: CC-BY 4.0. Questions, support, or data reports: hello@factreason.com.