← ablaut

The ablaut API

Verb conjugation for 20+ languages over HTTP or MCP. Every form is verified against two independent lexicons per language; answers are computed in microseconds by a native Rust engine.

Quickstart

curl -H "x-api-key: YOUR_KEY" \
  "https://api.ablaut.dev/v1/conjugate?verb=appeler&lang=fr"

{
  "verb": "appeler",
  "lang": "fr",
  "us": 42,
  "table": {
    "infinitive": "appeler",
    "present": ["appelle", "appelles", "appelle",
                "appelons", "appelez", "appellent"],
    "auxiliary": "avoir",
    ...
  }
}

Authentication

Every /v1 request needs an x-api-key header. Create a key in your account — the free tier allows 2,000 requests/day and 60/minute, shared across the API and MCP. Requests without a valid key get 401; over the limit returns 429.

Endpoints

GET /v1/conjugate

Responses include us, the engine compute time in microseconds. Errors: 400 missing verb, 401 bad key, 429 rate limit reached, 422 unknown language or a string that is not an infinitive of the requested language — ablaut only conjugates real verbs, it never invents forms:

{ "error": "not a supported French verb" }

GET /v1/lemma

Reverse lookup: ?form=suis&lang=fr returns every lemma whose paradigm contains the form, with the slots it occupies — ambiguity included (suis matches both être and suivre). Productive coverage for French, Spanish, German, and English; irregular forms reverse in all 14 languages. Every match is verified by forward conjugation, so a cited slot always really contains the form.

{ "form": "suis", "matches": [
  { "infinitive": "être",   "slots": ["present 1sg"] },
  { "infinitive": "suivre", "slots": ["present 1sg", "present 2sg", "imperative 2sg"] } ] }

GET /v1/languages

The 20+ languages with ISO codes and maturity status (beta: verified at 100% agreement against two gold lexicons; wip: known gaps under active work).

Response shapes per language

Each language's table mirrors its real morphology instead of forcing one template: German carries both Konjunktiv rows and separable-prefix forms, Czech carries aspect and its counterpart, Spanish the Rioplatense voseo, Irish returns fully composed and mutated rows, Swedish tenses are single forms rather than person arrays. The reference below is generated from live engine output at build time, so it cannot drift. Person arrays run 1sg → 3pl (German adds the polite Sie row on the site only). Analytic tenses composed from auxiliaries (passé composé, passato prossimo, perfekti) are part of the API response for every language except Danish, whose auxiliary coverage is still partial.

MCP

The same engine as an MCP server, for Claude Code, Cursor, or any MCP-capable agent:

claude mcp add ablaut --env ABLAUT_API_KEY=YOUR_KEY -- npx -y @v4nn4/ablaut-mcp

{
  "mcpServers": {
    "ablaut": {
      "command": "npx",
      "args": ["-y", "@v4nn4/ablaut-mcp"],
      "env": { "ABLAUT_API_KEY": "YOUR_KEY" }
    }
  }
}

Tools: conjugate(verb, language) returning the same table as the HTTP API, and list_languages(). Set ABLAUT_API_URL to point at another instance.

Machine-readable spec

OpenAPI 3.1: https://api.ablaut.dev/openapi.json. The library behind the API is open source: ablaut-dev/ablaut (Rust, Python, WebAssembly).