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Head-to-head · Formal Verification Tools

Lean vs TLA+

  • Updated Nov 2026
  • Both researched from official sources
  • 2 checks side by side
Higher score Lean #5 in Formal Verification Tools 9.1/10 Open source ✓ 1 of 2 features Visit Lean
TLA+ #8 in Formal Verification Tools 8.7/10 Open source ✓ 1 of 2 features Visit TLA+ site

Lean leads on 0 checks, TLA+ on 0, and 2 are even. Who comes out ahead on the 2 yes/no, price and count checks where we have data for both products. The editor score weighs everything else too.

Our verdict

  • Highest scoreLean · 9.1/10

Lean scores higher on our rubric for formal verification tools: 9.1 against 8.7 out of 10; our editors rank them #5 and #8.

On verification method, TLA+ gives you Hybrid where Lean offers Deductive. On supported formalisms, Lean gives you Theorem-proving where TLA+ offers Invariants.

Lean is the better fit for modern dependent-type verification. TLA+ is the better fit for distributed-system modeling and checking.

  • Lean fits best

    Modern dependent-type verification

  • TLA+ fits best

    Distributed-system modeling and checking

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Side by side

Feature Lean 9.1/10 Visit ↗ TLA+ 8.7/10 Visit ↗
At a glance
Editor score 9.1 8.7
Ranking #5 in Formal Verification Tools #8 in Formal Verification Tools
Best for Modern dependent-type verification Distributed-system modeling and checking
Pricing model Free Free
Starting price Open source Open source
Free plan Not checked yet Not checked yet
Free trial — —
Deployment Cloud, Self-hosted Cloud, Self-hosted, Desktop
Platforms Web, Windows, macOS, Linux Windows, macOS, Linux
Support Community, Docs Email, Community, Docs
Built for Solo, Small business, Mid-market, Enterprise Solo, Small business, Mid-market, Enterprise
Features Lean 1/2 · TLA+ 1/2
Counterexamples Not checked yet ✓ (best)
Proof artifacts ✓ (best) Not checked yet
Specs
Verification method Deductive Hybrid
Supported formalisms Theorem-proving Invariants
Input languages Lean 4 TLA+ and PlusCal
Deployment Both Both
Our review
Pros
  • Kernel-based checking produces independently checkable proof terms.
  • Tactics and metaprogramming support extensible proof automation.
  • Works across web, desktop, Linux, and self-hosted environments.
  • Combines TLC, Apalache, TLAPS, PlusCal, and IDE support
  • Checks safety, liveness, invariants, proofs, and error traces
  • Supports Windows, macOS, Linux, and local or other deployment modes
Cons
  • Its formalism focus is theorem-proving rather than a broad multi-formalism toolkit.
  • The listed editor integration is centered on Visual Studio Code.
  • Lean 4 is the listed input language for formalization workflows.
  • The legacy Eclipse-based Toolbox is described as unmaintained
  • Its formal models sit above the implementation level
  • Different verification needs span several distinct tools
Our verdict

Lean combines interactive theorem proving with a dependently typed functional programming language. It is intended for formalizing mathematics, verifying software and hardware, and developing reliable programs. The open-source distribution…

Read the review →

TLA+ is an open-source formal specification language and tool ecosystem for modeling software and hardware above the implementation level. It is especially suited to concurrent and distributed systems, where engineers need to express…

Read the review →
  1. LeanFormal Verification Tools 9.1Open source
  2. TLA+Formal Verification Tools 8.7Open source

Strengths and trade-offs

  • Lean — where it wins

    • Kernel-based checking produces independently checkable proof terms.
    • Tactics and metaprogramming support extensible proof automation.
    • Works across web, desktop, Linux, and self-hosted environments.

    Where it doesn't

    • Its formalism focus is theorem-proving rather than a broad multi-formalism toolkit.
    • The listed editor integration is centered on Visual Studio Code.
    • Lean 4 is the listed input language for formalization workflows.

  • TLA+ — where it wins

    • Combines TLC, Apalache, TLAPS, PlusCal, and IDE support
    • Checks safety, liveness, invariants, proofs, and error traces
    • Supports Windows, macOS, Linux, and local or other deployment modes

    Where it doesn't

    • The legacy Eclipse-based Toolbox is described as unmaintained
    • Its formal models sit above the implementation level
    • Different verification needs span several distinct tools

More comparisons

All formal verification tools comparisons → · Full ranking →

Reviewed by iTechGuides Editors · Editorial team · Updated Nov 2026

Last updated · How we research and update