Lean website screenshot

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 publishes 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 3 more developer resources.

🌐 Visit website 📡 Source on GitHub
19.4/100 emerging ▬ flat Agent 3/100 human only Full breakdown ↓
scored 2026-08-10 · rubric v0.9.1
AccessFreemium
1 APIs
Dependent TypesFormal VerificationProgramming LanguageTheorem Prover

Kin Score

Kin Score Kin Score How this is scored →
scored 2026-08-10 · rubric v0.9.1
Composite quality — 19.4/100 · emerging
Contract Quality 0.0 / 25
Developer Ergonomics 1.7 / 20
Commercial Clarity 7.9 / 20
Operational Transparency 4.8 / 13
Governance 0.0 / 12
Discoverability 5.0 / 10
Agent readiness — 3/100 · human only
Machine-Readable Contract 0 / 18
Agentic Access Contract 0 / 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/lean: 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 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

Company 1

The organization behind the API

Website
Website

Source (apis.yml)

apis.yml Raw ↑ 
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
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: '0.19'
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: 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