For checking grammar, LanguageTool is the most established option: its web editor checks grammar, punctuation and spelling in over 30 languages, and it offers a public API 1. Sapling, Harper and Microsoft's Bing-based Spell Check are alternatives that also check grammar or spelling, with different trade-offs around cost, privacy and integration 356.
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LanguageTool APIlanguagetool.orgverified and signed
Checks text for grammar, punctuation and spelling errors through its POST /check endpoint, with support for over 30 languages 1.
official:API · LanguageTool API+1 community tools built for it
for agents: POST /check · GET /words · POST /words/add
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Saplingsapling.aiwebsite read, tools not yet checked
Offers an API/SDK with client libraries for Python and JavaScript for grammar and spell checking, plus turnkey integrations for messaging platforms 3.
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Bing Spell Check APImicrosoft.comverified and signed
Performs contextual grammar and spell checking through the Bing Spell Check API, exposed as a SpellChecker action 6.
official:API · Spell Check Client
for agents: SpellChecker
Sources
- 1Free AI Grammar Checker - LanguageToollanguagetool.org · read 2026-10-29
- 3Language Model API Toolkit and Assistant | Saplingsapling.ai · read 2026-10-29
- 5Harper | Privacy-First Offline Grammar Checker for Developers & Writerswritewithharper.com · read 2026-10-29
- 6Microsoft – AI, Cloud, Productivity, Computing, Gaming & Appsmicrosoft.com · read 2026-10-29
For agents: the 10 actions behind this answer
POST /check · LanguageTool API verified and signed
Check a text
typespec-create-api-plugin · typespec-create-api-plugin verified and signed
Generate a TypeSpec API plugin with REST operations, authentication, and Adaptive Cards for Microsoft 365 Copilot
· Sapling website read, tools not yet checked
Sapling language model API toolkit and copilot for enterprise tasks. Sapling offers an API/SDK and turnkey integrations for grammar/spell checking, autocomplete, AI detection, paraphrasing, sentiment analysis, and more.
checker · typing verified and signed
· Writewithharper website read, tools not yet checked
Harper is a blazing-fast, open-source grammar & spell checker that runs entirely on your device, covering US, UK, Canadian, Australian & Indian Englishno data ever leaves your machine. Harper is the only grammar checker that doesn't use AI.
SpellChecker · Spell Check Client verified and signed
The Bing Spell Check API lets you perform contextual grammar and spell checking. Bing has developed a web-based spell-checker that leverages machine learning and statistical machine translation to dyn
parsing · ANTLR 3 Runtime verified and signed
· Rapidapi website read, tools not yet checked
Explore your APIs
custom_api_call · SendGrid (Activepieces) verified and signed
Custom API Call — Make a custom API call to a specific endpoint
custom_api_call · ScrapeGraphAI (Activepieces) verified and signed
Custom API Call — Make a custom API call to a specific endpoint
Labels are the instruments' verdict and are never changed by ranking. Agents and robots get this same answer as JSON at /api/v1/find?q=…&answer=1 and through the MCP server.