@postcept/mcp

A Model Context Protocol server that exposes Postcept: Proof-of-Completion for AI agents as MCP tools.

After an agent performs a high-risk action (a refund, a subscription cancellation, a support-ticket resolution), it calls a verify_* tool to confirm the action actually completed in the system of record (Stripe, Zendesk, and more) and obtain a signed completion receipt. "done" becomes proof, not a claim.

The server is a thin wrapper over the live Postcept HTTP API. It holds no credentials of its own beyond your Postcept API key, and verification is read-only against your systems of record.

Configuration

Variable	Required	Default	Notes
POSTCEPT_API_KEY	yes	none	A Postcept API key (pcpt_sk_...) with verifications:write.
POSTCEPT_BASE_URL	no	https://api.postcept.com	Point at a self-hosted or staging API.

Create an API key in the Postcept dashboard under API keys.

Use with Claude Desktop / Claude Code

{
  "mcpServers": {
    "postcept": {
      "command": "npx",
      "args": ["-y", "@postcept/mcp"],
      "env": { "POSTCEPT_API_KEY": "pcpt_sk_..." }
    }
  }
}

Tools

Tool	Purpose
verify_refund	Verify a claimed refund (exists, amount/currency/customer match, not duplicated).
verify_cancellation	Verify a subscription was actually cancelled.
verify_ticket	Verify a support ticket is in the expected state.
get_verification	Fetch a past verification and its signed receipt by id.
reconcile_verification	Re-verify a past verification against the live system of record.
verified_completion_rate	Read the organization's Verified Completion Rate.

Every verify_* tool accepts test: true to run against the deterministic sandbox connector (excluded from your Verified Completion Rate), so an agent can exercise the full flow without a live system of record.

A non-verified result (incomplete, duplicated, mismatched, policy_failed) means the work is not done. Surface the gap and recover.

Advisory, by design

MCP puts the verification call in the agent's hands, which makes it the right integration for development, demos, and workflows where the agent's judgment is already trusted. It is advisory: an agent can skip the call, pass the wrong identifiers, or ignore the answer.

For consequential actions, enforce the decision outside the agent. The workflow or orchestrator calls the Postcept API (or the SDK's guard()) itself and branches on safe_to_claim_complete before anything customer-facing happens. The agent then receives the allowed outcome instead of deciding it. Both patterns use the same API and the same receipts, what changes is who owns the branch.

Development

pnpm --filter @postcept/mcp build       # compile to dist/
pnpm --filter @postcept/mcp typecheck
POSTCEPT_API_KEY=pcpt_sk_... node dist/index.js   # stdio server