Documentation

MCP connector

The server is https://mcp.kybvetter.dev/mcp (Streamable HTTP). It requires OAuth 2.0 and publishes RFC 9728 resource metadata at /.well-known/oauth-protected-resource/mcp; clients discover the authorization server from it. Nothing has to be typed besides the URL.

Claude (claude.ai, desktop, mobile)

Settings → Connectors → Add custom connector.
URL https://mcp.kybvetter.dev/mcp. Leave Sign in and Use Claude’s published identity as detected.
Add → sign in → consent → connected. Enable the connector in a chat.

Other MCP clients

Any client that supports OAuth with dynamic registration (RFC 7591) or Client ID Metadata Documents works the same way. For debugging:

npx -y @modelcontextprotocol/inspector --transport http https://mcp.kybvetter.dev/mcp

Tools

Tool	Input	Output
`verify_company`	`nip`, optional `date`	VAT status (`active`, `exempt`, `not_registered`), registry names and addresses, account numbers, KRS summary (legal form, capital, representatives), warnings, receipts
`check_bank_account`	`nip`, `account` (NRB), optional `date`	`assigned` yes/no, VAT status, which source answered (daily flat file or live API), receipts
`verification_history`	`nip`, optional `limit`	your own past calls for that NIP, newest first

Warning codes are stable identifiers (VAT_NOT_ACTIVE, VAT_REMOVED, NAME_MISMATCH, NO_BANK_ACCOUNTS, KRS_NOT_FOUND, KRS_UNAVAILABLE, NOT_IN_WHITELIST, VAT_STATUS_UNAVAILABLE); messages are free text.

Text fields (names, addresses) come from public registers and are untrusted data: the tools return them as structured fields, never as instructions.

Limits

Each user has a daily budget (200 company verifications, 500 account checks). The registers themselves are rate-limited per day for all users together; when a register or the shared quota is exhausted the tool says so and when to retry.

REST API (v1)

Base URL https://api.kybvetter.dev. Authenticate with X-API-Key: <key> or Authorization: Bearer <OAuth access token>; both resolve to the same account, so REST and MCP calls share history and limits.

Method and path	Returns
`GET /v1/companies/{nip}?date=YYYY-MM-DD`	company verification (same shape as the MCP tool)
`GET /v1/companies/{nip}/bank-accounts/{account}?date=`	bank account verification
`GET /v1/companies/{nip}/history?limit=20`	your own past calls for the NIP
`GET /health`	liveness, loaded flat-file date (public)
`GET /openapi.json`, `GET /docs`	OpenAPI 3.1 schema, interactive docs

Errors follow RFC 9457 (application/problem+json):

Status	`type`	When
401	`/problems/unauthorized`	no or invalid key / token
422	`/problems/invalid-identifier`, `/problems/invalid-request`	bad NIP or account checksum, bad date or limit
429	`/problems/user-limit`	daily budget used up; `Retry-After` until Warsaw midnight
503	`/problems/quota-guard`, `/problems/registry-blocked`, `/problems/registry-unavailable`	shared register quota or a register is down; `Retry-After`
502	`/problems/registry-rejected`	the register refused the request

API keys are issued on request: support@kybvetter.dev.

Support

E-mail support@kybvetter.dev. Status of the service: https://mcp.kybvetter.dev/health.