specdrift

Deterministic spec lint for manifest-driven golden paths.

A golden path lives or dies by one promise: the manifest is the single source of truth. Schemas validate the manifest's shape and static analyzers guard the code — but nothing watches the space between artifacts, where "the manifest says X, the repo does Y" rots silently. That gap is exactly where AI-generated changes decay. specdrift is the lint layer for that gap, and it is deliberately boring: it never calls an LLM — LLMs call it.

dotnet tool install -g specdrift

specdrift validate .platform/manifest.yaml --schema manifest.schema.json --rules rules.yaml

Run it anywhere

How	One line
.NET tool	dotnet tool install -g specdrift
Docker (any stack)	docker run --rm -v "$PWD:/work" -w /work ghcr.io/omercelikdev/specdrift:0.4.1 <args>
GitHub Action	- uses: omercelikdev/specdrift@v0.4.1 with args:
MCP server (agents)	docker run --rm -i ghcr.io/omercelikdev/specdrift:0.4.1 mcp — stdio tools spec_validate, spec_drift

The image is multi-arch (amd64 + arm64). The engine is generic: the schema, rules and drift profiles are DATA — point them at any repository, any language.

What it does (v1)

• validate — JSON-Schema validation of a YAML/JSON manifest plus cross-field invariants you declare as data (rules.yaml): "when this path contains that value, this other path must exist." Every finding has a rule id, a severity, and a message that teaches the fix. Output: human text or --format json; exit code is the contract (0 clean · 1 findings · 2 usage/IO).

  Schema evaluation is an in-tree, dependency-free evaluator for the pragmatic 2020-12 subset manifests actually use (type · enum · const · required · properties · additionalProperties · unevaluatedProperties · oneOf/anyOf/allOf/not · if/then/else · $ref(#/…) · pattern · min/maxLength · min/maximum · items · uniqueItems · min/maxItems). An unknown assertion keyword is a hard fail — the engine never guesses. Reports are noise-free by design: a failed if merely deselects its branch, and a failed oneOf yields ONE finding at the decision point, not one per alternative. (Why in-tree: every candidate library failed this project's own gates — one ships a maintenance-fee EULA in its NuGet binaries, one compiles code at runtime, one silently skips if/then.)

• drift — manifest ↔ repository reality, driven by a drift profile (.specdrift/drift.yaml): a feature enabled with its package or wiring call absent (each direction has its own finding — including "referenced but not enabled" dead weight), committed API documents diverging semantically from built ones, and manifest schema-version skew. Detection is TEXTUAL by design and says so; reports, never auto-fixes.

  # .specdrift/drift.yaml
  version: 1
  manifest: .platform/manifest.yaml
  schemaVersion: 1
  wiring:
    - feature: features.outbox
      package: Platform.Messaging
      call: AddPlatformOutbox
    - feature: providers.auth       # value-gated wiring
      equals: openid
      package: Platform.Auth
      call: AddPlatformAuth
  openapi:
    - committed: specs/openapi.json
      built: artifacts/openapi.json

• mcp — the same two verbs served over stdio MCP (spec_validate, spec_drift), so coding agents ask the engine instead of guessing. Register it like any stdio server:

  { "mcpServers": { "specdrift": { "command": "specdrift", "args": ["mcp"] } } }

Profiles are data, the engine is generic

specdrift knows nothing about any particular platform. The schema, the invariant rules and (coming with drift) the wiring tables are profile data that each golden path ships in its own repository:

# rules.yaml
version: 1
rules:
  - id: SPEC0101
    description: L2 caching needs a redis connection name
    when: { path: features.distributedCaching.levels, op: contains, value: l2 }
    require: { path: features.distributedCaching.redis.connectionName }
    severity: error
    message: "features.distributedCaching.levels includes 'l2' but redis.connectionName is missing - name the connection the cache should use."

Supported when ops: exists, equals, contains (array membership or substring). Constraints: require (path must exist and be non-empty) and forbid (path must be absent). A rule without when applies unconditionally.

Determinism contract

• Same inputs → byte-identical report. No network, no clocks in output, no LLM.
• Unknown manifest schema versions are a hard fail — the engine never guesses forward.

License

MIT.