LanguageTool website screenshot

LanguageTool

Open-source grammar, style, and spell checking REST API supporting 25+ languages with AI-powered error detection, style suggestions, and text improvements. Used by 100+ companies to enhance software with proofreading capabilities via a simple HTTP API returning JSON responses. Hosted on GDPR-compliant servers in Germany with no text storage.

LanguageTool publishes 3 APIs on the APIs.io network: Check API, Languages API, and Words API. Tagged areas include Grammar, Spell Check, Style, Proofreading, and NLP.

The LanguageTool catalog on APIs.io includes 1 Spectral governance ruleset.

LanguageTool’s developer surface includes documentation, engineering blog, pricing, and 9 more developer resources.

🌐 Visit website 📡 Source on GitHub
35.3/100 thin ▼ -5.8 Agent 22/100 agent aware Full breakdown ↓
scored 2026-07-28 · rubric v0.6
AccessFreemium
3 APIs
GrammarSpell CheckStyleProofreadingNLPNatural Language ProcessingWritingOpen Source

Kin Score

Kin Score Kin Score How this is scored →
scored 2026-07-28 · rubric v0.6
Composite quality — 35.3/100 · thin
Contract Quality 8.1 / 25
Developer Ergonomics 2.2 / 20
Commercial Clarity 10.0 / 20
Operational Transparency 0.7 / 13
Governance 7.0 / 12
Discoverability 7.4 / 10
Agent readiness — 22/100 · agent aware
Machine-Readable Contract 18 / 18
Agentic Access Contract 10 / 10
MCP Server 0 / 12
Machine-Readable Auth 0 / 10
Idempotency 0 / 9
Stable Error Semantics 0 / 8
Request/Response Examples 0 / 7
Rate-Limit Signaling 7 / 7
Typed Event Surface 0 / 6
Agent Skills 0 / 5
Well-Known Catalog 0 / 4
Consent & Bot Identity 0 / 3
A2A Agent Card 0 / 8
Dry-Run / Simulate Mode 0 / 4
Improve this rating by publishing the missing artifacts — every area above can be raised, and the full rubric is at apis.io/rating/. This rating is computed from github.com/api-evangelist/languagetools: open an issue to ask a question, or submit a pull request to add artifacts. Want it done for you? Prioritized profiling — $2,500 →

APIs 3

Individual APIs this provider publishes, each with its own machine-readable definition.

LanguageTool Check API

The Check API from LanguageTool — 1 operation(s) for check.

LanguageTool Languages API

The Languages API from LanguageTool — 1 operation(s) for languages.

LanguageTool Words API

The Words API from LanguageTool — 3 operation(s) for words.

Pricing Plans 1

Published pricing tiers and plan structures.

Plans

6 plans

PLANS

Rate Limits 1

Documented rate limits and quota policies.

Rate Limits

0 limits

RATE LIMITS

FinOps 1

Cost, billing, and metering signals for API financial operations.

Finops

FINOPS

Spectral Rules 1

Spectral governance rulesets for linting and validating these APIs.

LanguageTool API Rules

5 rules · 3 warnings 2 info

SPECTRAL

JSON Schema 4

Standalone JSON Schema definitions for this provider's data models.

CheckRequest

14 properties

JSON SCHEMA

CheckResponse

3 properties

JSON SCHEMA

Language

3 properties

JSON SCHEMA

WordsResponse

1 properties

JSON SCHEMA

Examples 4

Example request and response payloads for these APIs.

Check Markup Request

2 fields

EXAMPLE

Check Text Request

3 fields

EXAMPLE

Check Text Response

3 fields

EXAMPLE

Words Add Request

3 fields

EXAMPLE

Security Posture 1

Authentication, domain security, vulnerability disclosure, and trust-center signals.

Languagetools Domain Security

TLSv1.3 · DMARC

SECURITY

Agentic Access 1

Recommended x-agentic-access execution contracts for AI agents.

Languagetools Agentic Access

5 operations · 3 acting

5 operations · 3 acting

AGENTIC

Resources

Documentation 1

Reference material describing how the API behaves

Documentation
Documentation

Agent Surfaces 1

MCP servers, agent skills, and machine-readable catalogs

AgenticAccess
AgenticAccess

Build 1

SDKs, sample code, and the tooling you integrate with

GitHubOrg
GitHubOrg

Access & Security 1

Authentication, authorization, and security posture

DomainSecurity
DomainSecurity

Operate 1

Status, limits, changes, and where to get help

RateLimits
RateLimits

Commercial 3

Pricing, plans, and the legal terms of use

Pricing
Pricing
 Plans
Plans
 FinOps
FinOps

Company 3

The organization behind the API

Website
Website
 LinkedIn
LinkedIn
 Blog
Blog

Other 1

Properties that don't map to a standard resource type

X
X

Source (apis.yml)

apis.yml Raw ↑ 
aid: languagetools
name: LanguageTool
description: Open-source grammar, style, and spell checking REST API supporting 25+ languages with AI-powered error detection,
  style suggestions, and text improvements. Used by 100+ companies to enhance software with proofreading capabilities via
  a simple HTTP API returning JSON responses. Hosted on GDPR-compliant servers in Germany with no text storage.
accessModel:
  pricing: freemium
  onboarding: unknown
  trial: false
  try_now: false
  public: false
  label: Freemium
  confidence: medium
  source:
  - plans
  generated: '2026-07-22'
  method: derived
image: https://kinlane-images.s3.amazonaws.com/shared/apis-json/icons/languagetools.png
url: https://raw.githubusercontent.com/api-evangelist/languagetools/refs/heads/main/apis.yml
created: '2026-06-13'
modified: '2026-06-13'
specificationVersion: '0.19'
type: Index
tags:
- Grammar
- Spell Check
- Style
- Proofreading
- NLP
- Natural Language Processing
- Writing
- Open Source
apis:
- aid: languagetools:languagetools-check-api
  name: LanguageTool Check API
  description: The Check API from LanguageTool — 1 operation(s) for check.
  humanURL: https://languagetool.org/http-api/
  baseURL: https://api.languagetool.org/v2
  tags:
  - Check
  properties:
  - type: OpenAPI
    url: openapi/languagetools-check-api-openapi.yml
  - type: Documentation
    url: https://languagetool.org/http-api/
- aid: languagetools:languagetools-languages-api
  name: LanguageTool Languages API
  description: The Languages API from LanguageTool — 1 operation(s) for languages.
  humanURL: https://languagetool.org/http-api/
  baseURL: https://api.languagetool.org/v2
  tags:
  - Languages
  properties:
  - type: OpenAPI
    url: openapi/languagetools-languages-api-openapi.yml
  - type: Documentation
    url: https://languagetool.org/http-api/
- aid: languagetools:languagetools-words-api
  name: LanguageTool Words API
  description: The Words API from LanguageTool — 3 operation(s) for words.
  humanURL: https://languagetool.org/http-api/
  baseURL: https://api.languagetool.org/v2
  tags:
  - Words
  properties:
  - type: OpenAPI
    url: openapi/languagetools-words-api-openapi.yml
  - type: Documentation
    url: https://languagetool.org/http-api/
common:
- type: AgenticAccess
  url: agentic-access/languagetools-agentic-access.yml
- type: DomainSecurity
  url: security/languagetools-domain-security.yml
- type: Website
  url: https://languagetool.org
- type: Documentation
  url: https://languagetool.org/http-api/
- type: GitHubOrg
  url: https://github.com/languagetool-org
- type: LinkedIn
  url: https://www.linkedin.com/company/languagetool
- type: Blog
  url: https://languagetool.org/insights/
- type: Pricing
  url: https://languagetool.org/proofreading-api
- type: X
  url: https://x.com/languagetoolorg
- type: Plans
  url: https://raw.githubusercontent.com/api-evangelist/languagetools/refs/heads/main/plans/plans.yml
- type: RateLimits
  url: https://raw.githubusercontent.com/api-evangelist/languagetools/refs/heads/main/rate-limits/rate-limits.yml
- type: FinOps
  url: https://raw.githubusercontent.com/api-evangelist/languagetools/refs/heads/main/finops/finops.yml
maintainers:
- FN: Kin Lane
  email: kin@apievangelist.com