Lowkey.

Lowkey API

The tax knowledge base of Lowkey,
directly in your own software.

Search Dutch tax legislation, case law, decrees and parliamentary documents from your own software or chat assistant. One key per firm, search is free, research EUR 0.50 per call.

Request an API key See the services No subscription. Pay per use.

§ 01 / Platform

API or MCP: what is the difference?

The REST API is for software: your portal, filing package or in-house tool calls the knowledge base and gets JSON back. The MCP server is for chat assistants: advisers connect Claude or ChatGPT and ask their questions in plain language. Same knowledge base, same key, same price per call.

  REST API MCP server
Purpose Build the knowledge base into your own software Use the knowledge base from a chat assistant
Who uses it Your developer or software vendor Every adviser at the firm, no developer needed
Connecting HTTPS calls with a Bearer key Server URL plus the same key in Claude or ChatGPT
Cost Search free · research EUR 0.50 per call Identical: the price is per call, not per channel
REST API · curl
# you receive the base URL with your API key curl "$LOWKEY_API_BASE/v1/search" \ -H "Authorization: Bearer $LOWKEY_API_KEY" \ -G --data-urlencode "q=30% ruling duration"
MCP · remote server config
{ "mcpServers": { "lowkey": { "url": "https://<base-url>/mcp", "headers": { "Authorization": "Bearer <your key>" } } } }

§ 02 / Services

Services on the platform

01
Live

Tax knowledge base

Validated corpus of Dutch tax sources: legislation, case law, decrees and parliamentary documents. Four endpoints, also available as MCP tools.

  • GET /v1/search: search the corpus · free
  • GET /v1/sources/:id: retrieve a source · free
  • GET /v1/status: corpus status · free
  • POST /v1/research: evidence-backed answer with citations · EUR 0.50 per call
02
Early access · on request

30% ruling application

Send employee and employer data (or documents), receive the complete application package for the Dutch tax authority back: the completed form and the accompanying cover letter. The firm keeps its own intake, client relationship and branding.

This endpoint is not yet generally available. Get in touch to discuss early access.

Roadmap: fiscal unity CIT and VAT, the RGS bridging file and more services will follow on the same platform.

§ 03 / Pricing

Pricing

Per firm · excl. VAT · no subscription

Free: knowledge base search & sources (API + MCP) Fair use up to 200 calls per day per firm EUR 0.00
Research Per research call, invoiced after the fact, minimum invoice amount EUR 10 EUR 0.50 / call
30% application package Early access EUR 12.50 / package
Subscription 0.00

No subscription. You pay per use: free for search within the fair-use limit, per call for research, per completed package for the 30% ruling.

§ 04 / Fair use & terms

Fair use and terms

Rate limits
Apply at key and firm level. Systematic copying or scraping of the corpus is not permitted.
EU only
Processing takes place exclusively on EU-based infrastructure.
No storage
No client data is stored beyond what is needed for the service.

A data processing agreement is available for the 30% ruling application endpoint, since employee and employer data passes through it.

Access

Request an API key

One key per firm, on request. Email which services you want to use; you will receive the key and the base URL to connect by mail.

Request an API key