Lean

Lean is an open-source theorem prover and programming language based on dependent type theory, designed for formal verification of mathematics and software. It supports interactive proof development and is used by mathematicians and computer scientists.

Lean is listed with 1 API on the APIs.io network. Tagged areas include Dependent Types, Formal Verification, Programming Language, and Theorem Prover.

Lean’s developer surface includes documentation and 6 more developer resources.

🌐 Visit website 📡 Profile data on GitHub

8.6/100 minimal ▬ flat Agent 1/100 human only Front door AI 5/6 prominent Full breakdown ↓
scored 2026-10-31 · rubric v0.25.0 · Show this score on your site →

AccessFreemium

1 API

Dependent TypesFormal Verification Programming LanguageTheorem Prover

Kin Score

Kin Score How this is scored →
scored 2026-10-31 · rubric v0.25.0

Composite quality — 8.6/100 · minimal

Contract Quality 0.0 / 21

Developer Ergonomics 1.6 / 17

Access Clarity 1.3 / 17

Operational Transparency 1.5 / 11

Contract Governance 0.0 / 10

Discoverability 4.1 / 9

Regulatory Posture 0.9 / 15

Agent readiness — 1/100 · human only

Machine-Readable Contract 0 / 18

Agentic Access Contract 0 / 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 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

Delegated User Identity 0 / 6

Protected Resource Metadata 0 / 5

Registration Without a Human 0 / 6

Agentic Commerce Well-Known Document 0 / 5

Pagination 5 / 5

Distinct Operations 3 / 3

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 could not be measured. We hold no machine-readable contract for this provider to read, so there is nothing to measure a write surface against. Excluded rather than scored zero: never-measured and measured-empty are different facts. Publishing an OpenAPI is what makes this facet — and several others — scorable at all.

The six quality facets above are damped to 85 points between them, because the conditional facet above carries the other 15. That is why each facet's contribution is shown against a damped maximum: raising a quality facet moves the composite by 85% of its nominal weight, not 100%. The full arithmetic is at apis.io/rating/.

Show this score on your site.

It updates itself when the score changes. Paste this where you link to your API docs:

<a href="https://apis.io/providers/lean/"><img src="https://apis.io/badge/lean/card.svg" alt="Lean on APIs.io — Kin Score by API Evangelist"></a>

Other styles, a README pill and a shields.io endpoint are on the badge page.

Raise your score.

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

Machine-Readable Contract +18 pts — api_specs includes an OpenAPI document
MCP Server +12 pts — deployment.mode + probe verdict on the mcp/ manifest, not the pointer; an unprobed slug falls back to authorship
Agentic Access Contract +10 pts — agentic_access artifact present (x-agentic-access), graded by author
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)
A2A Agent Card +8 pts — a2a/-a2a.yml manifest, graded on conformance.grade against A2A 1.0.0

12 more unmet checks in the Agent Readiness table above.

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

Contract Quality scores 0.0 — up to +25.0 composite points
Access Clarity scores 7.9 — up to +18.4 composite points
Developer Ergonomics scores 9.5 — up to +18.1 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/lean/apis.yml: open an issue on github.com/api-evangelist/lean 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 →

APIs 1

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

Lean

Lean theorem prover and programming language for formal verification of mathematics and software.

Pricing Plans 1

Published pricing tiers and plan structures.

Lean Plans Pricing

3 plans

PLANS

Rate Limits 1

Documented rate limits and quota policies.

Lean Rate Limits

5 limits

RATE LIMITS

FinOps 1

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

Lean Finops

FINOPS

Security Posture 1

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

Lean Domain Security

TLSv1.3 · HSTS · DNSSEC

SECURITY

Resources

Documentation 1

Reference material describing how the API behaves

Documentation

Documentation

Build 1

SDKs, sample code, and the tooling you integrate with

GitHubOrganization

GitHubOrganization

Access & Security 1

Authentication, authorization, and security posture

DomainSecurity

DomainSecurity

Operate 1

Status, limits, changes, and where to get help

RateLimits

RateLimits

Commercial 2

Pricing, plans, and the legal terms of use

Plans

Plans

FinOps

FinOps

Company 1

The organization behind the API

Website

Website

Source (apis.yml)

aid: lean
name: Lean
description: Lean is an open-source theorem prover and programming language based on dependent type theory, designed for formal
  verification of mathematics and software. It supports interactive proof development and is used by mathematicians and computer
  scientists.
type: Index
deliveryModel:
  model: unknown
  open_source: false
  commercial: false
  callable_host: false
  label: Delivery model not determined — needs a product licence on record
  confidence: low
  source:
  - none
  generated: '2026-08-28'
  method: derived
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/lean.png
tags:
- Dependent Types
- Formal Verification
- Programming Language
- Theorem Prover
url: https://raw.githubusercontent.com/api-evangelist/lean/refs/heads/main/apis.yml
created: '2025-01-01'
modified: '2026-04-28'
specificationVersion: '0.23'
apis:
- aid: lean:lean
  name: Lean
  description: Lean theorem prover and programming language for formal verification of mathematics and software.
  humanURL: https://lean-lang.org/
  tags:
  - Formal Verification
  - Theorem Prover
  properties:
  - type: Documentation
    url: https://lean-lang.org/documentation/
common:
- type: Plans
  url: plans/lean-plans-pricing.yml
- type: RateLimits
  url: rate-limits/lean-rate-limits.yml
- type: FinOps
  url: finops/lean-finops.yml
- type: DomainSecurity
  url: security/lean-domain-security.yml
- type: Website
  url: https://lean-lang.org/
- type: Documentation
  url: https://lean-lang.org/documentation/
- type: GitHubOrganization
  url: https://github.com/leanprover/lean4
maintainers:
- FN: Kin Lane
  email: kin@apievangelist.com

Lean API — frequently asked questions

Does Lean have an API?

Yes. APIs.io lists 1 API from Lean, including Lean.

How much does the Lean API cost?

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

Is the Lean API ready for AI agents?

Lean has a Kin Score of 8.6 out of 100 (minimal) and an Agent Readiness score of 0.6 (human-only), scored by API Evangelist on 2026-10-31.

Work with this as data

Every provider here is available over the APIs.io API and to AI agents over MCP.

MCP server

One button, every client — Claude, Cursor, VS Code and the rest.

https://apis.io/mcp

Tools for providers

9 MCP tools reach this

find_providersBrowse and filter every provider in the catalog.
get_provider_artifactsEvery artifact this provider publishes, grouped by type.
get_provider_operationsEvery operation across all of their OpenAPIs — one call instead of parsing every spec.
get_provider_toolsEvery MCP tool they ship, with the operation each wraps.
get_provider_evidenceHow each part of their score was established. Free — the basis for a claim should not sit behind it.
get_provider_ratingPRO — composite, band, trend and facet scores.
apis_io_searchSTART HERE — APIs, providers and tags for one query, each with its total.
resolveTurn a domain, URL or GitHub org into the provider it belongs to.
find_cohortsEvery scored population of providers in the catalog.

All 92 tools →

Call it yourself

curl for this page

This provider

curl "https://apis.io/api/v1/providers/lean"

All providers

curl "https://apis.io/api/v1/providers?limit=25"

Every operation they expose

curl "https://apis.io/api/v1/providers/lean/operations?limit=25"

How their score was established

curl "https://apis.io/api/v1/providers/lean/evidence"

Discovery needs no key. Ratings and market analysis are Pro.

Get an API key

Free tier, no form to fill in. Signing in shares your email address with us — we store it to create your key and to recognise you if you sign in with another provider. See our Privacy Policy and Terms.

GitHub Google LinkedIn

A second provider on the same verified email joins the account you already have.