wunderspec 0.134.1

Protocol specifications as Python code

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.

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

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

:bulb: 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.

Feature	Open Core	Premium
Symbolic expression evaluator	✅	✅
wunderspec lint	✅	✅
wunderspec run	✅	✅
wunderspec replay	✅	✅
wunderspec convert	✅	✅
wunderspec check	✅	✅
wunderspec with-tlc	✅	✅
wunderspec with-apalache	✅	✅
wunderspec fuzz	❌	✅
wunderspec rust	❌	✅
wunderspec lean	❌	✅

4. Release Provenance

• Release tag: v0.134.1
• Source commit: c9ee963d884f34db1ae946b8dec869d9c7a80c76

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

5. Latest Release Notes

Changes since public release v0.132.2.

• When an @example property is checked but no witness state is found, run, check, fuzz, replay, with-tlc, and with-apalache now report the outcome as warning: No examples found … (previously the misleading success: …) and exit with the dedicated code 3. The exit-code scheme is now 0 = clean / no predicate, 1 = invariant violation, 2 = example found, 3 = example not found. Invariant checks are unaffected: holding an invariant is still success / exit 0.
• Add per-action profiling to wunderspec run and check. By default they now print a compact fired/tried (pct%) table, sorted by action name, counting how many times each non-inline (@action(inline=False)) action was entered (tried) and completed without violating an assumption (fired). Actions whose fire rate is at or near 0% are highlighted in red when color is enabled. Pass --no-action-profiling to disable the accumulation and the table.
• Improve wunderspec run trace coverage on specifications whose actions depend on hard-to-hit guards. Add --max-retries-per-step (default 30): the per-trace retry budget is --max-retries-per-step × --max-steps, and a trace is cut only when it reaches --max-steps or exhausts that budget. The earlier consecutive-failure cutoff, which abandoned still-progressing traces too early, has been removed. run now also prints Trace length statistics: max=…, min=…, average=… at the end.

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.