Wunderspec

Wunderspec is a Python DSL for writing and checking executable specifications.

Distributed systems often fail due to unforeseen issues: message reordering, race condition, stale observations, retry behavior, crashes and restarts, network outages, vibe code. Adding more example tests is often not enough to find these bugs before they make it to production. Specifications written in Wunderspec surface these issues early, so that teams find design flaws before they become production incidents.

This is the open-core distribution.

📋 Wunderspec in 5 minutes: the Wunderspec in Five Minutes gives you a quick overview of the core concepts.

📋 Cheatsheet: the Wunderspec cheatsheet summarizes the DSL and CLI in a few pages — keep it open while you work.

💡 Using Quint? Try this command:

uv tool install wunderspec
wunderspec convert --from=spec.qnt --to=spec.py --main=main

1. Wunderspec in Action

Follow Bob in his Wunderspec adventure. There, Bob writes a specification of a write-ahead log, finds a bug, replays the counterexample and fixes the specification.

2. Installation

Using uv:

uv tool install wunderspec

After installation, the CLI is available:

wunderspec --help

If you want to add Wunderspec as a dependency, just type:

uv add wunderspec
uv sync

3. Features

This open-core package includes the features marked ✅ in the Open Core column. Premium-only command names stay visible for discoverability, but those commands are not included in this package.

4. Release Provenance

• Release tag: v0.137.3
• Source commit: be86a4dd5da2668b37f5287a80ab13ef025b645c

See tests/README.md for the development test log captured at release time.

5. Latest Release Notes

Changes since public release v0.137.1.

• Fix AST pickle loading that could execute arbitrary code through builtins.eval and other globals. Allow only explicit AST and sort classes and the internal AST enums; reject pickle extensions that bypass the class allowlist.
• Deprecate save_ast and load_ast in favor of wunderspec.transfer, planned for v0.138.0. Load pickle files only if you produced them yourself.

6. License

Wunderspec is distributed under the Functional Source License, Version 1.1, with an Apache 2.0 future license (FSL-1.1-ALv2). See LICENSE.