Table of Contents

Using SEK as a Spec Kit extension

SEK ships as a Spec Kit community extension (sek; release asset spec-kit-sek.zip). It adds model-based testing to the spec-driven development (SDD) lifecycle: turn a feature's acceptance criteria into an executable model, explore it for edge cases, and verify that your implementation conforms.

  • Category: code  •  Effect: read-write
  • Commands: /speckit.sek.model, /speckit.sek.explore, /speckit.sek.verify
  • Agent skills: sek-cord-authoring, using-sek-to-generate-tests

Prerequisites

  • Spec Kit (specify) installed.
  • .NET SDK 10.0.303.
  • The sek tool: dotnet tool install -g SpecExplorerKit.Tool.

Install the extension

specify extension add sek \
  --from https://github.com/stuartpa/sek/releases/latest/download/spec-kit-sek.zip

For local development against a checkout of this repo:

specify extension add --dev ./extensions/spec-kit-sek

The installed extension is self-contained: its implementation-accurate Cord and downstream consumer skills live under .specify/extensions/sek/skills/. Consumers should load those resources rather than copying SEK language documentation into their own products.

The commands

/speckit.sek.model

Reads the active feature's spec.md (especially the acceptance criteria) and generates a SEK model program plus a Cord scenario, then scaffolds the project and runs sek validate. Category effect: creates model/Cord/config files.

/speckit.sek.explore

Builds the model and runs sek explore, then summarizes the transition system (states, transitions, accepting states, coverage) and renders a diagram you can drop into plan.md or a pull request.

/speckit.sek.verify

Runs sek test to replay the exploration against your implementation via a binding, and reports conformance (TEST PASSED / TEST FAILED). Use it as a gate before marking a feature's tasks complete.

Where it fits in the SDD lifecycle

flowchart LR
    S[/speckit.specify/] --> M[/speckit.sek.model/]
    M --> P[/speckit.plan/]
    P --> X[/speckit.sek.explore/]
    X --> I[/speckit.implement/]
    I --> V[/speckit.sek.verify/]
    V -->|conforms| Done((done))
    V -->|fails| I
  1. Specify the feature as usual.
  2. Model it (/speckit.sek.model) — the acceptance criteria become an explorable model.
  3. Plan and explore (/speckit.sek.explore) — review reachable behavior and edge cases before writing code.
  4. Implement, then verify (/speckit.sek.verify) — gate on conformance.

Configuration

The commands operate on a .specexplorerkit/config.json in the feature folder — see Project configuration.

Publishing / catalog

The extension's catalog metadata is prepared in extensions/catalog.community.json. Per Spec Kit's Extension Publishing Guide, submit it via the Extension Submission issue template (do not PR the catalog directly). The release provides the spec-kit-sek.zip asset that the catalog's download_url points at.

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