Harmonic

Harmonic is a Palo Alto AI lab building Mathematical Superintelligence (MSI) — AI that reasons with rigorous, verifiable logic rather than statistical pattern matching. Its flagship product, Aristotle, is a formal reasoning agent that uses Lean 4 to prove and formally verify graduate- and research-level problems in mathematics and software. Developers access Aristotle through the Aristotle API (https://aristotle.harmonic.fun) and the official Python SDK/CLI (aristotlelib): submit Lean 4 proof files with `sorry` placeholders, plain English math problems, or LaTeX research papers, and Aristotle attempts to complete, formalize, and formally verify them — running autonomously for up to 24 hours on larger tasks and returning only formally checked results. Harmonic was co-founded by Vlad Tenev (co-founder of Robinhood) and Tudor Achim, and is backed by Kleiner Perkins.

Harmonic publishes 1 API on the APIs.io network. Tagged areas include Company, Ai, Mathematics, Formal Verification, and Theorem Proving.

Harmonic’s developer surface includes signup flow, engineering blog, authentication, CLI, changelog, and 13 more developer resources.

🌐 Visit website 📡 Source on GitHub
27.5/100 emerging Agent 21/100 agent aware Full breakdown ↓
scored 2026-07-20 · rubric v0.4
1 APIs 1 MCP Servers 0 Features
CompanyAiMathematicsFormal VerificationTheorem ProvingLeanMachine ReasoningDeveloper Tools

API Rating

API Evangelist API Evangelist Rating How this is scored →
scored 2026-07-20 · rubric v0.4
Composite quality — 27.5/100 · emerging
Contract Quality 0.0 / 25
Developer Ergonomics 8.7 / 20
Commercial Clarity 6.8 / 20
Operational Transparency 2.7 / 13
Governance 0.0 / 12
Discoverability 9.3 / 10
Agent readiness — 21/100 · agent aware
Machine-Readable Contract 0 / 18
Agentic Access Contract 0 / 15
MCP Server 12 / 12
Machine-Readable Auth 10 / 10
Idempotency 0 / 9
Stable Error Semantics 0 / 8
Request/Response Examples 0 / 7
Rate-Limit Signaling 0 / 7
Typed Event Surface 0 / 6
Agent Skills 0 / 5
Well-Known Catalog 0 / 4
Consent & Bot Identity 0 / 3
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/harmonic: 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

Aristotle API

Programmatic access to Aristotle, Harmonic's formal reasoning agent. Over HTTPS with an API key, submit Lean 4 proofs with `sorry` placeholders, natural-language math problems, ...

MCP Servers

harmonic-mcp.yml

MCP SERVER

Resources

Get Started 3

Portal, sign-up, and the first successful call

DeveloperPortal
DeveloperPortal
 SignUp
SignUp
 Login
Login

Agent Surfaces 2

MCP servers, agent skills, and machine-readable catalogs

MCPServer
MCPServer
 LLMsTxt
LLMsTxt

Design & Contract 2

Pagination, idempotency, versioning, errors, and events

Conventions
Conventions
 Lifecycle
Lifecycle

Build 4

SDKs, sample code, and the tooling you integrate with

GitHubOrganization
GitHubOrganization
 Packages
Packages
 SDKs
SDKs
 CLI
CLI

Access & Security 2

Authentication, authorization, and security posture

Authentication
Authentication
 DomainSecurity
DomainSecurity

Operate 1

Status, limits, changes, and where to get help

ChangeLog
ChangeLog

Commercial 2

Pricing, plans, and the legal terms of use

TermsOfService
TermsOfService
 PrivacyPolicy
PrivacyPolicy

Company 2

The organization behind the API

Website
Website
 Blog
Blog

Source (apis.yml)

apis.yml Raw ↑ 
aid: harmonic
name: Harmonic
description: 'Harmonic is a Palo Alto AI lab building Mathematical Superintelligence (MSI) — AI that reasons with rigorous,
  verifiable logic rather than statistical pattern matching. Its flagship product, Aristotle, is a formal reasoning agent
  that uses Lean 4 to prove and formally verify graduate- and research-level problems in mathematics and software. Developers
  access Aristotle through the Aristotle API (https://aristotle.harmonic.fun) and the official Python SDK/CLI (aristotlelib):
  submit Lean 4 proof files with `sorry` placeholders, plain English math problems, or LaTeX research papers, and Aristotle
  attempts to complete, formalize, and formally verify them — running autonomously for up to 24 hours on larger tasks and
  returning only formally checked results. Harmonic was co-founded by Vlad Tenev (co-founder of Robinhood) and Tudor Achim,
  and is backed by Kleiner Perkins.'
url: https://raw.githubusercontent.com/api-evangelist/harmonic/refs/heads/main/apis.yml
x-type: company
x-source: kleiner-perkins-portfolio
x-tier: enriched
x-tier-reason: portfolio-lead
specificationVersion: '0.20'
image: https://www.harmonic.fun/images/harmonic-blue.svg
created: '2026-07-17'
modified: '2026-07-19'
tags:
- Company
- Ai
- Mathematics
- Formal Verification
- Theorem Proving
- Lean
- Machine Reasoning
- Developer Tools
apis:
- name: Aristotle API
  description: Programmatic access to Aristotle, Harmonic's formal reasoning agent. Over HTTPS with an API key, submit Lean
    4 proofs with `sorry` placeholders, natural-language math problems, or LaTeX papers; Aristotle fills sorries, formalizes
    documents into Lean 4, and returns only formally verified results. The API is asynchronous — submit a job and poll/download
    the result — and is driven primarily through the official aristotlelib Python SDK and `aristotle` CLI.
  humanURL: https://aristotle.harmonic.fun
  baseURL: https://aristotle.harmonic.fun
  tags:
  - Formal Verification
  - Theorem Proving
  - Lean
  - Mathematics
  properties:
  - type: SignUp
    url: https://aristotle.harmonic.fun/auth/login?screen_hint=signup
  - type: Login
    url: https://aristotle.harmonic.fun/auth/login
maintainers:
- FN: Kin Lane
  email: kin@apievangelist.com
- FN: APIs.json
  email: info@apis.io
common:
- type: Website
  url: https://www.harmonic.fun
- type: DeveloperPortal
  url: https://aristotle.harmonic.fun
- type: SignUp
  url: https://aristotle.harmonic.fun/auth/login?screen_hint=signup
- type: Login
  url: https://aristotle.harmonic.fun/auth/login
- type: TermsOfService
  url: https://aristotle.harmonic.fun/terms
- type: PrivacyPolicy
  url: https://aristotle.harmonic.fun/privacy
- type: Blog
  url: https://harmonic.fun/news
- type: GitHubOrganization
  url: https://github.com/harmonic-ai
- type: Authentication
  url: authentication/harmonic-authentication.yml
- type: Packages
  url: packages/harmonic-packages.yml
- type: SDKs
  url: packages/harmonic-packages.yml
- type: CLI
  url: cli/harmonic-cli.yml
- type: MCPServer
  url: mcp/harmonic-mcp.yml
- type: LLMsTxt
  url: llms/harmonic-llms.txt
- type: Conventions
  url: conventions/harmonic-conventions.yml
- type: ChangeLog
  url: changelog/harmonic-changelog.yml
- type: Lifecycle
  url: lifecycle/harmonic-lifecycle.yml
- type: DomainSecurity
  url: security/harmonic-domain-security.yml
x-enrichment:
  date: '2026-07-19'
  status: backfilled
  pass: local-v1
  note: backfilled from .gitignore signal + verified work evidence