LanguageTool

LanguageTool is an open-source proofreading and grammar checking tool that supports more than 25 languages. The HTTP API enables developers to programmatically check texts for grammar and style issues, list supported languages, and manage personal dictionaries.

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

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

LanguageTool’s developer surface includes documentation, GitHub presence, and 10 more developer resources.

🌐 Visit website 📡 Profile data on GitHub

29.5/100 thin ▬ flat Agent 19/100 agent aware Front door AI 4/6 moderate Heartbeat 100/100 alive open core · LGPL-2.1 Full breakdown ↓
scored 2026-11-06 · rubric v0.27.0 · Show this score on your site →

AccessFreemium

1 published contract

Grammar Language Proofreading Spell CheckStyle CheckText Analysis

Kin Score

Kin Score How this is scored →
scored 2026-11-06 · rubric v0.27.0

Composite quality — 29.5/100 · thin

Contract Quality 10.0 / 19

Developer Ergonomics 1.4 / 15

Access Clarity 4.3 / 15

Operational Transparency 1.3 / 10

Contract Governance 0.9 / 9

Discoverability 5.0 / 8

Regulatory Posture 2.1 / 15

Create-or-Update Ergonomics 0.0 / 10

Agent readiness — 19/100 · agent aware

Machine-Readable Contract 18 / 18

Agentic Access Contract 10 / 10

Documented Reversibility 0 / 6

MCP Server 0 / 12

Machine-Readable Auth 0 / 10

Idempotency 0 / 9

Stable Error Semantics 0 / 8

Request/Response Examples 7 / 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

Delegated User Identity 0 / 6

Protected Resource Metadata 0 / 5

Registration Without a Human 0 / 6

Agentic Commerce Well-Known Document 0 / 5

Pagination 0 / 5

Distinct Operations 3 / 3

MCP Tool Quality 6 / 6

Regulatory Posture applies to this provider. Its tags matched the Horizontal (data, software, accessibility, platform) regime, so Regulatory Posture carries 15 points of the composite. If this regime is wrong for your business, say so on your provider repo — the applicability map is public and we will correct it.

Create-or-Update Ergonomics applies to this provider. This API accepts writes, so it carries 10 points of the composite. It is scored from the published contracts themselves: whether a caller can create-or-update in one call, whether the write accepts a key the caller already holds, and whether the response says which branch ran. Without that, every write needs a search-and-branch in front of it, and the first time that check is skipped a duplicate record is created. Scored against the observed mean rather than raw — a provider at the catalog average is unchanged by this facet, not penalised by it.

The six quality facets above are damped to 75 points between them, because the conditional facet above carries the other 25. That is why each facet's contribution is shown against a damped maximum: raising a quality facet moves the composite by 75% of its nominal weight, not 100%. The full arithmetic is at apis.io/rating/.

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Agent readiness — checks not met, largest first (exact, from this profile):

MCP Server +12 pts — deployment.mode + probe verdict on the mcp/ manifest, not the pointer; an unprobed slug falls back to authorship
Machine-Readable Auth +10 pts — a served openid-configuration/oauth-authorization-server carrying `issuer` (served), else the securitySchemes class in the provider OpenAPIs — bound (mutualTLS, DPoP, Signature) > negotiable (oauth2 authorizationCode/clientCredentials, openIdConnect) > bearer (http bearer, apiKey)
Idempotency +9 pts — OpenAPI mutating operations declare an idempotency key — a header, a request-body property, or a named de-duplication token whose own description says so (verified); else common[].type matches /idempoten/i (documented)
Stable Error Semantics +8 pts — OpenAPI $refs a shared error schema across 4xx/5xx responses (verified), else common[].type includes ErrorCatalog / ErrorCodes / DeclineCodes
A2A Agent Card +8 pts — a2a/-a2a.yml manifest, graded on conformance.grade against A2A 1.0.0
Registration Without a Human +6 pts — a `registration_endpoint` in the served RFC 8414 / OIDC discovery document

10 more unmet checks in the Agent Readiness table above.

Kin Score — facets with the most composite points still available (weight × headroom):

Developer Ergonomics scores 9.5 — up to +18.1 composite points
Access Clarity scores 28.9 — up to +14.2 composite points
Contract Quality scores 53.1 — up to +11.7 composite points

Each check links to what satisfies it. Publish the artifact, or tell us where it already lives, and the score moves on the next scoring run.

Improve this rating by publishing the missing artifacts — every area above can be raised, and the full rubric is at apis.io/rating/. Every facet and dimension name above is a link: it opens that measurement's own page — what it means, the exact checks that feed it, how the whole catalog distributes on it, and the providers at the top of it. This rating is computed from the provider profile at artifacts.apis.io/languagetool/apis.yml: open an issue on github.com/api-evangelist/languagetool to ask a question or point us at an artifact you publish. Submit an artifact on GitHub — free → Manage your own listing — the Influence plan, $499/mo →

Markets this provider is in provisional

The Kin Score Market layer reads a provider inside its market: its position, and how deep its integrations go. Depth is only comparable within a position. Provisional and unweighted: not part of the Kin Score or agent readiness.

Market	Position	Depth	Registered MCP server	Declares compatibility
Browser Extension Stores (company-published Firefox add-ons; Chrome Web Store unreadable)	mixed	34.9	-	-
Raycast Store Extensions (first-party publishers + community-wrapped products)	mixed	34.9	-	-
Obsidian Community Plugins (third-party APIs the Obsidian plugin ecosystem integrates)	mixed	34.9	-	-
APIs.guru OpenAPI Directory (API definition directory)	mixed	34.9	-	-

Registered MCP server and declares compatibility are report only — not weighted. Undeclared means we found nothing we can read, so there is no number: we never infer integrations.

Standards implemented 1

Standards this provider implements or carries. De facto ones are profiled and measured by the API Commons; formal ones come from the standards directory and are linked by the provider's own tags. The evidence column says how each claim was established — not that it was made.

OpenAPI

measured — observed by APIs.io (published)

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.

Open Collections 4

Open, tool-agnostic API collections (OpenAPI-derived and Bruno).

LanguageTool HTTP Check API

OPEN COLLECTION

LanguageTool HTTP Check Languages API

OPEN COLLECTION

LanguageTool HTTP Check Words API

OPEN COLLECTION

LanguageTool HTTP API

OPEN COLLECTION

LanguageTool API pricing

Not yet checked against LanguageTool's own pricing page. Compiled by API Evangelist on 2026-05-04; confirm before you rely on a figure. A free plan or tier is listed.

Plan	Price
Free freemium	Free
Professional paid	Free
Enterprise enterprise	—

Plan details, limits and sources →

Rate limits

Free Tier Default: 10 requests per minute
Free Tier Monthly Quota: 1000 requests per month
Professional Tier Default: 100 requests per minute

Compiled by API Evangelist, not yet checked against LanguageTool's documentation. All 5 limits →

Pricing Plans 1

Published pricing tiers and plan structures.

Languagetool Plans Pricing

3 plans

PLANS

Rate Limits 1

Documented rate limits and quota policies.

Languagetool Rate Limits

5 limits

RATE LIMITS

Service Levels 1

Uptime the provider promises or reports, as SLA4OAI. Read from its own pages; APIs.io runs no monitors.

LanguageTool

SLA

FinOps 1

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

Languagetool Finops

FINOPS

Spectral Rules 1

Spectral governance rulesets for linting and validating these APIs.

LanguageTool — jsonschema rules

5 rules · 3 warnings 2 info

SPECTRAL

JSON Schema 1

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

LanguageTool Match

8 properties

JSON SCHEMA

Security Posture 1

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

Languagetool Domain Security

TLSv1.3 · DMARC

SECURITY

Agentic Access 1

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

Languagetool Agentic Access

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

GitHub

GitHub

Access & Security 1

Authentication, authorization, and security posture

DomainSecurity

DomainSecurity

Operate 1

Status, limits, changes, and where to get help

RateLimits

RateLimits

Commercial 4

Pricing, plans, and the legal terms of use

Plans

FinOps

PrivacyPolicy

TermsOfService

Company 2

The organization behind the API

LinkedIn

Website

Website

Other 1

Properties that don't map to a standard resource type

Developer

Developer

Source (apis.yml)

aid: languagetool
name: LanguageTool
description: LanguageTool is an open-source proofreading and grammar checking tool that supports more than 25 languages. The
  HTTP API enables developers to programmatically check texts for grammar and style issues, list supported languages, and
  manage personal dictionaries.
type: Index
deliveryModel:
  model: open-core
  license: LGPL-2.1
  license_evidence:
    repo: languagetool-org/languagetool
    spdx: LGPL-2.1
    stars: 15087
  open_source: true
  commercial: true
  callable_host: true
  label: Open core · an OSS project plus a commercial hosted product
  confidence: medium
  source:
  - openapi
  - pricing
  - repository-license
  generated: '2026-09-25'
  method: derived
accessModel:
  pricing: freemium
  onboarding: unknown
  trial: false
  try_now: false
  public: false
  label: Freemium
  confidence: low
  source:
  - plans
  - security
  generated: '2026-11-06'
  method: derived
position: Consuming
access: 3rd-Party
image: https://kinlane-images.s3.amazonaws.com/shared/apis-json/icons/languagetool.png
tags:
- Grammar
- Language
- Proofreading
- Spell Check
- Style Check
- Text Analysis
created: '2025-02-08'
modified: '2026-05-19'
url: https://raw.githubusercontent.com/api-evangelist/languagetool/refs/heads/main/apis.yml
specificationVersion: '0.23'
apis:
- aid: languagetool:languagetool-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/languagetool-check-api-openapi.yml
  - type: Documentation
    url: https://languagetool.org/http-api/
  - type: SwaggerUI
    url: https://languagetool.org/http-api/swagger-ui/
  - type: JSONSchema
    url: json-schema/languagetool-match-schema.json
- aid: languagetool:languagetool-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:
  - Language
  tags_raw:
  - Languages
  properties:
  - type: OpenAPI
    url: openapi/languagetool-languages-api-openapi.yml
  - type: Documentation
    url: https://languagetool.org/http-api/
  - type: SwaggerUI
    url: https://languagetool.org/http-api/swagger-ui/
  - type: JSONSchema
    url: json-schema/languagetool-match-schema.json
- aid: languagetool:languagetool-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:
  - Word
  tags_raw:
  - Words
  properties:
  - type: OpenAPI
    url: openapi/languagetool-words-api-openapi.yml
  - type: Documentation
    url: https://languagetool.org/http-api/
  - type: SwaggerUI
    url: https://languagetool.org/http-api/swagger-ui/
  - type: JSONSchema
    url: json-schema/languagetool-match-schema.json
common:
- type: Plans
  url: plans/languagetool-plans-pricing.yml
- type: RateLimits
  url: rate-limits/languagetool-rate-limits.yml
- type: FinOps
  url: finops/languagetool-finops.yml
- type: AgenticAccess
  url: agentic-access/languagetool-agentic-access.yml
- type: DomainSecurity
  url: security/languagetool-domain-security.yml
- type: LinkedIn
  url: https://www.linkedin.com/company/languagetool
- type: Website
  url: https://languagetool.org
- type: Documentation
  url: https://languagetool.org/http-api/
- type: Developer
  url: https://dev.languagetool.org/
- type: GitHub
  url: https://github.com/languagetool-org/languagetool
- type: PrivacyPolicy
  url: https://languagetool.org/legal/privacy
- type: TermsOfService
  url: https://languagetool.org/legal/terms
maintainers:
- FN: Kin Lane
  email: kin@apievangelist.com

LanguageTool API — frequently asked questions

Does LanguageTool have an API?

Yes. APIs.io lists 3 APIs from LanguageTool, including LanguageTool Check API, LanguageTool Languages API and LanguageTool Words API.

Is there an OpenAPI specification for the LanguageTool API?

Yes. APIs.io indexes 3 OpenAPI specifications for LanguageTool, each linked for download from this page.

How much does the LanguageTool API cost?

APIs.io lists 3 pricing plans for LanguageTool, with each plan's price, limits and inclusions under Pricing on this page.

Is the LanguageTool API ready for AI agents?

LanguageTool has a Kin Score of 29.5 out of 100 (thin) and an Agent Readiness score of 19.0 (agent-aware), scored by API Evangelist on 2026-11-06.

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