TLA+
TLA+ is a free, open-source language and toolset for modeling software and hardware, particularly concurrent and distributed systems.
What TLA+ is
TLA+ is a free, open-source language and toolset for modeling software and hardware, particularly concurrent and distributed systems. Its tools help identify fundamental design errors in a specification before they become difficult or expensive to address in code. Users can describe algorithms in PlusCal and translate them into TLA+ models. TLC checks executable specifications for safety and liveness properties, including runs distributed across computers or cloud systems, while TLAPS mechanically checks TLA+ proofs. The TLA+ Toolbox supports editing, translation, model checking, error-trace exploration, and proof work. A Visual Studio Code extension adds syntax highlighting, translation, parsing, TLC runs, result visualization, completion, and formatting. Command-line tools are available through tla2tools.jar and require Java 11 or later. The tools and Toolbox repository use the MIT License. The Eclipse-based Toolbox GUI is currently unmaintained, has minor unfixed bugs, and relies on its help pages as its only user manual.
Good
- Models software and hardware systems
- TLC checks safety and liveness properties
- TLAPS mechanically checks proofs
- VS Code extension supports TLA+ and PlusCal
Watch out
- Command-line tools require Java 11 or later
- Eclipse-based Toolbox GUI is currently unmaintained
- Toolbox has minor unfixed bugs
- Toolbox help pages are its only user manual
Who it suits
TLA+ suits teams modeling concurrent or distributed systems and checking designs before implementation. It offers both model-checking and proof-checking workflows, with interfaces for the Toolbox, VS Code, and command line.
Verdict
TLA+ provides several ways to describe and verify system designs, from TLC model checking to mechanically checked proofs. The Toolbox’s maintenance and documentation limitations are worth considering when choosing an interface.
Plans and prices
From TLA+'s own pricing page, checked 9 Oct 2026.
| Plan | Price | What it gives you |
|---|---|---|
| TLA+ | Free | Open-source specification language and tools · command-line tools require Java 11+ |
The facts
Each one read from TLA+'s own pages, with the date it was checked.
What it does
- Command line and Java
- The tools can run from the command line using tla2tools.jar and require Java 11 or later.checked 9 Oct 2026
- Design verification
- TLA+ and its tools are intended to help find fundamental design errors that can be difficult and expensive to correct in code.checked 9 Oct 2026
- Editor integration
- A Visual Studio Code extension supports TLA+ and PlusCal syntax highlighting, translation, parsing, TLC runs, result visualization, code completion, and formatting.checked 9 Oct 2026
- IDE features
- The TLA+ Toolbox supports editing specifications, running the PlusCal translator and TLC, exploring error traces, and running the proof system.checked 9 Oct 2026
- Known limitations
- The Toolbox page notes that it has minor unfixed bugs and that its help pages are its only user manual.checked 9 Oct 2026
- License
- The TLA+ tools and Toolbox repository is licensed under the MIT License.checked 9 Oct 2026
- Model checking
- TLC checks executable TLA+ specifications for safety and liveness properties and can run across multiple computers or cloud systems.checked 9 Oct 2026
- PlusCal
- PlusCal describes algorithms and translates them into TLA+ models that can be checked with TLA+ tools.checked 9 Oct 2026
- Proof checking
- TLAPS mechanically checks proofs written in TLA+.checked 9 Oct 2026
- Purpose
- TLA+ is a high-level language for modeling software and hardware systems, especially concurrent and distributed systems.checked 9 Oct 2026
- Support
- The TLA+ Foundation directs technical questions and issues to the appropriate GitHub issue tracker.checked 9 Oct 2026
- Toolbox maintenance
- The repository describes the Eclipse-based Toolbox GUI as currently unmaintained.checked 9 Oct 2026
Where it runs
- Platforms
- The Toolbox download instructions cover Windows, Mac OS, and Linux.checked 9 Oct 2026
