Understand
Build an accurate model of what a workflow actually does — its states, handlers, and the orderings they admit — from the code you already wrote.
SpecCraft
Understand, verify, and test complex concurrent and durable-execution workflows — where the dangerous bugs live in interleavings no test suite ever samples.
The problem
Section titled “The problem”Durable-execution platforms like Temporal made workflows-as-code the right default for anything that must survive crashes, retries, and long waits. But once a workflow grows many interleaving signals, timers, and handlers, it becomes genuinely hard to reason about, test, and trust.
The dangerous bugs aren’t the non-deterministic crashes the runtime already catches. They’re logical races: domain invariants that quietly break under an ordering nobody ever exercised — and that no test suite samples.
What it does
Section titled “What it does ”SpecCraft is tooling to understand, verify, and test complex concurrent and durable-execution workflows — closing the gap between a tool that comprehends workflow logic and one that checks it.
Verify
Check domain invariants against every interleaving, not just the happy path your tests happen to hit. In the lineage of TLA+ and deterministic simulation.
Test
Exercise the orderings no hand-written test would think to sample, and surface the ones that break.
Built for durable execution
Targets Temporal first — workflows-as-code where state survives crashes, retries, and long waits.
Why now
Section titled “Why now”Durable execution is becoming the default substrate for backend systems, and the correctness gap grows with it. AI accelerates the shift: agentic systems are long-running and non-deterministic, so they demand durable execution — and most agent frameworks now build on one, with the agent itself deciding at runtime which steps fire, driving the very interleavings where the dangerous bugs live. Existing tools force a choice: formal methods that verify but require you to re-model your system by hand, or test frameworks that run real code but only sample the orderings you anticipated. SpecCraft aims to do both — from the workflow code itself.
Join the waitlist
Section titled “Join the waitlist”SpecCraft is in early development. Drop your email to hear when it’s ready — and to help shape what we build.
SpecCraft is built by Oleksandr Zalizniak. Follow along on GitHub or get in touch: alex@zalizniak.com.