LanguageTool

API

Grammar, style and spelling check API for 30+ languages, hosted or self-hosted

Price: Free self-host; hosted API plans paid
Access: None; username and key on paid plans

About

Open-source (LGPL) proofreading engine with a JSON HTTP API that flags grammar, style and spelling errors in 30+ languages. Use the hosted API (servers in Germany) or run the Java server yourself; the free public endpoint is rate-limited, and AI-based rules are cloud-only.

What you can do with it

Check user-written text for grammar, spelling and style errors in 30+ languages
Run your own grammar-check server so text never leaves your infrastructure
Show error offsets and replacement suggestions as underlines in a text editor

Get started

Download LanguageTool and start languagetool-server.jar on port 8081
Or POST text to the public API at api.languagetool.org/v2/check

Example

curl -X POST "https://api.languagetool.org/v2/check" \
  --data-urlencode "text=This are a example sentence." \
  --data "language=en-US"

Details

Hosting: Hosted service, Self-hosted
Available in: Worldwide
Official SDKs: Java
MCP server: None