Verified standard parts for AI coding agents. The agent writes only the seams.
Agents regenerate the same infrastructure on every project — slightly differently every time, unverified, unmaintained. PartKit packages each capability as a part: vendored code with a machine-readable contract, a conformance suite every adapter must pass, and a continuously re-issued attestation.
The catalog
Every part ships a contract, a conformance suite, seams documentation an agent can wire from without reading the source, and an attestation that expires — “verified” always means recently.
Append-only domain event log over a part-owned Postgres table, written and queried through a contract-stable interface and a driver-free SqlExecutor seam.
Send transactional email through a contract-stable interface with pluggable, attested vendor adapters.
Fixed-window API rate limiting through a contract-stable interface, with a built-in per-instance in-memory store and a typed pluggable-store seam for Redis-compatible backends.
Presigned, direct-to-storage uploads and downloads for any S3-compatible provider, via in-part AWS Signature Version 4 — no SDK, no proxying bytes through the app.
Verify inbound webhooks — HMAC signature, timestamp window, replay defense — through a contract-stable interface with pluggable, attested signature-scheme adapters.
The flip
Contracts erase the developer-experience differences between vendors. Switching email providers is a one-commit policy change — lockfile, selected adapter, one env line. Zero seam changes, because the contract didn’t move.
How it works
The agent asks, the registry plans
Over MCP: resolve_plan(capabilities, lockfile) returns a deterministic install order, env keys, and exactly which seams the app must write. One provider per capability per repo — sprawl is a resolver error.
Parts are vendored, not hidden
partkit add copies the part into your repo — you own every line, you can read every line. The lockfile pins the content hash the attestation signs.
The boundary holds
A pre-commit hook and CI guard make interiors read-only in practice; partkit verify checks every attestation offline. Integrity failures fail hard. Staleness only warns — our bad weekend never reddens your CI.
The wall
When an agent pattern-matches a type error into “let me edit the library,” it hits the boundary — and learns, in context, how the system works.