# Feature Specs

> Create and manage feature specifications that capture WHAT a feature does and WHY, without prescribing HOW to implement it.

- Skill: `lefant/feature-specs` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add lefant/feature-specs`
- Raw SKILL.md: https://api.skillmd.com/api/skills/lefant/feature-specs/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: lefant (https://skillmd.com/u/lefant)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/lefant/feature-specs

---


# Feature Specs Skill

Use this skill when creating or working with feature specifications. Feature specs capture intent (WHAT and WHY) before implementation begins.

This skill is the replacement for the old `spec_create` command.

## Purpose

Feature specs define what a feature should do and why it matters, without prescribing how to implement it. They serve as contracts between stakeholders and developers, and as living documentation that evolves with the product.

## When to Create a Spec

Create a feature spec when:
- Starting work on a new feature
- Clarifying requirements before implementation
- Documenting expected behavior for testing
- Aligning stakeholders on feature scope

Skip specs for:
- Bug fixes (unless behavior is unclear)
- Routine maintenance
- Implementation details (those go in ADRs)

## Directory Layout

Specs are stored in `./docs/specs/` at the project root. Create this directory on demand when writing the first spec.

## Default Workflow

When the user wants a new spec or wants an existing spec refined:
1. Determine the feature name and target filename
2. Create `./docs/specs/` if it does not exist
3. Clarify the user intent before drafting
4. Explore 1-2 realistic alternatives if they materially affect scope or behavior
5. Draft the spec in small sections:
   - Purpose
   - Requirements
   - Open Questions
6. Validate the draft with the user when the task is interactive
7. Write or update the spec using `template.md`

This skill should capture WHAT and WHY, not implementation details.

## File Naming Convention

`<feature-name>.md` - lowercase, dash-separated

Examples:
- `user-authentication.md`
- `export-to-csv.md`
- `rate-limiting.md`

## Template

See `template.md` in this skill directory for the spec format.

## Writing Guidelines

### Focus on WHAT, not HOW

- **Good**: "The system SHALL validate email format before submission"
- **Bad**: "The system SHALL use a regex to check emails"

Implementation decisions belong in ADRs, not specs.

### Use Normative Language

- **SHALL**: Required behavior (must have)
- **SHOULD**: Recommended behavior (should have)
- **MAY**: Optional behavior (nice to have)

### Write Scenarios in GIVEN/WHEN/THEN

```
GIVEN a user is logged in
WHEN they click "Export"
THEN a CSV file downloads containing their data
```

Include error scenarios:
```
GIVEN invalid credentials
WHEN user attempts login
THEN system displays error message without revealing which field is wrong
```

### Keep It Brief

- Purpose: 1-2 sentences
- Requirements: One SHALL/SHOULD/MAY statement each
- Scenarios: 2-4 per requirement (happy path + key edge cases)
- Aim for scannable, not exhaustive

### Embrace Open Questions

Open Questions are first-class citizens, not failures. It's better to document uncertainty than to guess:

```markdown
## Open Questions
- [ ] Should rate limiting apply per-user or per-API-key?
- [ ] What's the acceptable latency for export operations?
```

Resolve questions before or during implementation, then update the spec.

## Living Documents

Specs evolve. When reality diverges from the spec:
1. Update the spec to match the new understanding
2. Use git history to track how requirements changed
3. Don't maintain outdated specs—they become misleading

Changes are managed via git branches, not versioned filenames.

## Relationship to ADRs

| Specs | ADRs |
|-------|------|
| WHAT the system does | WHY we chose this approach |
| Behavior and intent | Implementation decisions |
| User-facing requirements | Technical tradeoffs |
| Living documents | Immutable records |

Cross-reference when relevant:
```
See: docs/decisions/2026-01-14_use-postgres-for-persistence.md
```

## Skill Activation

This skill activates when:
- Discussing new features in conversation
- Planning work before implementation
- Clarifying requirements or expected behavior
- User asks "what should this do?" or "how should this behave?"

## Creating a Spec

Treat requests like these as direct triggers for this skill:
- "Write a spec for user authentication"
- "Document the requirements for CSV export"
- "Create docs/specs/rate-limiting.md"