Spec Driven

Spec-Driven Development

A lightweight entrypoint for a collaborative human-agent methodology where requirements, decisions, and work are documented in a specs/ folder that serves as the project's single source of truth.

Read this skill first. Then load deeper references only when the current task needs them.

Skill Dependencies

This skill is part of a set of five skills designed to work together:

If any of these skills are missing from the project, instruct the user to install them before proceeding:

npx skills add b12consulting/skills --skill <missing_skill>

Core Rules

1. Specs are the ground truth. When code and specs disagree, the specs win. Either update the code or create an ADR to change the specs.
2. Major decisions are explicit. Scope, architecture, and trade-off changes require human confirmation and, when appropriate, an ADR.
3. Work stays traceable. Tickets should explain not just WHAT changed, but WHY, including durable findings discovered during implementation and review.
4. Document progressively. Create and update documents as the work evolves. Do not wait until the end to capture material assumptions, frictions, or follow-up candidates.
5. Surface drift immediately. If implementation or review reveals disagreement between code and specs, call it out and resolve it instead of silently diverging.

Truth Hierarchy

When documents conflict, the higher-level document takes precedence:

Vision.md > PRD.md > Architecture/ > Ticket Spec.md > Ticket Plan.md

If documents conflict, resolve it by either:

• creating an ADR and updating the higher-level document
• creating a ticket to fix the lower-level document or code

Minimal Document Map

• Project-level docs define the stable ground truth: README.md, Vision.md, PRD.md, Architecture/, Glossary.md, Changelog.md, and decisions/.
• Vision.md carries the long-lived purpose and direction: vision, problem statement, target audience, success metrics, and milestones.
• Ticket-level docs capture the lifecycle of a work item: Spec.md, Plan.md, and optional supporting files such as Research.md, Decisions.md, and Findings.md.
• Spec.md is the ticket anchor. It carries ticket metadata, summary, user stories, acceptance criteria, and scope.
• Plan.md is required. It carries the implementation strategy, risks, and execution checklist.
• Findings.md is curated. Use it for durable implementation discoveries such as assumptions, frictions, workarounds, follow-up candidates, and residual risks. Every finding needs a disposition.

Drift Detection

At the start of every conversation on a project with specs/:

1. Read specs/README.md, then Vision.md, PRD.md, and Architecture/README.md.
2. If the work touches entities, payloads, signals, public structs, APIs, or persisted read models, also read the relevant architecture sub-documents such as Architecture/data-model.md and any other topic-specific architecture docs that define long-lived boundaries.
3. If the current code or task contradicts these documents, alert the user immediately.
4. Resolution options:
   • create an ADR to update the specs if the code is right and the specs are outdated
   • create a ticket to fix the code if the specs are right and the code has drifted

Read More Only When Needed

• references/methodology.md — detailed document rules, lifecycle guidance, ADR policy, drift handling, and Findings guidance
• references/templates.md — document templates

Use a concise and to the point writing style

Be respectful of the fact that the human needs to read, understand and approve the spec files. Don't add unnecessary detail or verbosity.

Which Skill Next?

• Setting up specs — load specs-setup, then read the methodology reference and templates as needed.
• Creating or resuming a ticket — load specs-tickets, then read the methodology reference and templates as needed.
• Auditing the overall health of specs — load specs-review, then read the methodology reference as needed.
• Closing an implemented ticket — load specs-finish-ticket, then read the methodology reference as needed.

This skill intentionally stays lightweight. Use the methodology reference when you need operational detail.