spec-driven-implementation

SKILL.md

spec-driven-implementation

Drive a spec-first workflow for substantial features in Warp.

Overview

Use this skill for significant features where a written spec will improve implementation quality, reduce ambiguity, or make review easier. Be pragmatic: not every change needs specs.

Specs should usually live in:

specs/<linear-ticket-number>/PRODUCT.md

specs/<linear-ticket-number>/TECH.md

For example:

specs/APP-1234/PRODUCT.md

specs/APP-1234/TECH.md

specs/ should contain only ticket-named directories as direct children. Do not create engineer-named subdirectories or feature-slug directories there.
If a relevant Linear issue does not already exist, create one before writing specs. Use the Linear MCP tools directly:

list_teams to find the appropriate team

list_issue_labels to inspect the expected labels/tags

save_issue to create the issue with the appropriate team and labels

If the correct team or labels are not obvious from the request and surrounding context, use ask_user_question to clarify rather than guessing.

These specs should largely be written by agents, not by hand, and should be checked into source control so they can be reviewed and kept current with the code.

When specs are required

Strongly prefer specs when the change is substantial, such as:

product or architectural ambiguity

expected implementation size around 1k+ LOC

deep or cross-cutting stack changes

risky behavior changes where regressions would be expensive

work where agent quality will improve materially from clearer inputs

Specs are often unnecessary for:

small, local bug fixes

straightforward refactors

narrow UI tweaks with little ambiguity

For pure UI changes, the product spec is often useful while the tech spec may be unnecessary.

Workflow

1. Decide whether the feature needs specs

Evaluate the size, ambiguity, and risk of the feature. If specs will not meaningfully improve execution or review, skip them and focus on verification instead.

2. Write the product spec first

Before implementation, create PRODUCT.md describing the desired user-facing behavior.

Use the write-product-spec skill to produce it. The product spec should define:

what problem is being solved

the desired user experience

invariants and edge cases

success criteria

how the behavior will be validated

If the feature has UI or interaction design, ask for a Figma mock if one exists. If there is no mock, continue but call that out explicitly in the product spec.

Reference the Linear issue in the spec when one exists. Because specs live under specs/<linear-ticket-number>/..., this should usually be straightforward.

3. Write the tech spec when warranted

Use the write-tech-spec skill for substantial or ambiguous implementation work.

Prefer a tech spec when:

the implementation spans multiple subsystems

architecture or extensibility matters

there are meaningful tradeoffs to document

reviewers will benefit more from reviewing the plan than the raw code

It is acceptable to write the tech spec after an e2e prototype if that leads to a more accurate implementation plan. Do not force a premature tech spec when the implementation details are still too uncertain.

4. Implement approved specs

After the specs are approved, use the implement-specs skill to build from the approved PRODUCT.md and TECH.md.

The implementation can often be pushed in the same PR as the product and tech specs. As the engineer iterates, keep PRODUCT.md, TECH.md, code changes, and tests in that same PR so the review reflects the feature that will actually ship.

For large features, the implementer may optionally offer:

PROJECT_LOG.md to track explored paths, checkpoints, and current implementation state

DECISIONS.md to capture concrete product and technical decisions made during design and implementation

These are optional aids, not required outputs.

5. Keep specs current during implementation

If implementation changes from the spec, update the spec rather than leaving it stale.

Update PRODUCT.md when:

user-facing behavior changes

success criteria change

UX details or edge cases change

Update TECH.md when:

the implementation approach changes

architectural boundaries move

risks, dependencies, or rollout details change

the testing or validation plan changes

The checked-in specs should describe the feature that actually ships, not just the initial intent. Keep those spec updates in the same PR as the related code changes whenever practical.

6. Verify behavior against the spec

Before considering the work complete, make sure verification maps back to the specs. Prefer tests and artifacts that validate the product behavior directly:

unit tests and regression coverage that follow the repository's local testing conventions

integration tests for critical user flows

loom walkthroughs or equivalent feature demonstrations when appropriate

screenshots or videos when useful for UI-heavy work

Best Practices

Be pragmatic above all else.

Write specs to improve input quality for agents, not as ceremony.

Keep product specs behavior-oriented and implementation-light.

Keep tech specs implementation-oriented and grounded in current codebase patterns.

When a spec references relevant code chunks, include the inspected commit SHA in the file reference when possible and link the reference to the exact GitHub blob/<sha>/...#Lx-Ly lines.

Use review time to validate specs and behavior, not to over-index on code style nits.

Related Skills

implement-specs

write-product-spec

write-tech-spec