Overview
Based on Shape Up by Ryan Singer (Basecamp). A feature spec is not a PRD. A PRD justifies building something. A spec tells engineers exactly what to build - but at the right altitude. Shape Up's principle: give engineers a shaped problem with clear boundaries, not a detailed recipe. Ambiguity in the spec becomes a bug in production. Over-specification kills ownership.
Workflow
Step 1: Write the header
# Feature Spec: [Feature Name]
**PM:** [your name]
**Eng Lead:** [engineer name]
**Appetite:** [1-2 weeks / 4-6 weeks]
**Status:** Draft | In Review | Approved
**Related PRD / Ticket:** [link]
Step 2: Write the Problem (2-3 sentences)
What is broken or missing? Who is affected? Shape Up framing: "Jobs to be done" - what job is the user hiring this feature to do?
Step 3: Write the Solution at the right altitude
Shape Up's "fat marker sketch" - describe the solution broadly. Engineers need room to make technical decisions. Write at the level of user-visible behavior, not implementation.
Structure:
- Key interactions - what users can do (not how)
- Boundaries - explicit scope limits
- Rabbit holes - specific traps to avoid
Step 4: Write Functional Requirements
Number each. Cover in order:
- Happy path
- Error states
- Empty states
- Edge cases
Step 5: Write Non-Functional Requirements
Only include what's genuinely constrained:
- Performance targets
- Accessibility level (WCAG AA minimum)
- Browser/device support
- Security or compliance requirements
Don't pad. If there's no real constraint, don't list one.
Step 6: Define No-Gos (Shape Up)
Explicit list of what this spec does NOT include. This is Shape Up's most important contribution to spec writing - stating what you're NOT building is as important as what you are.
Step 7: List Open Questions
Q: [question]
Owner: [name]
Due: [date]
No spec should be approved with unresolved questions. Assign owners.
Step 8: Link assets
Figma files, API specs, data models. A spec without visuals is incomplete for UI work.
Anti-Patterns
1. Over-specifying implementation
Bad: "The button is blue, 48px, positioned top-right with 16px margin."
Good: "Users can trigger X from the main action area. Exact placement per Figma [link]."
Shape Up: over-speccing removes creative ownership from engineers and designers.
2. Missing error states
Bad: "User submits the form and sees confirmation."
Good: Cover success, validation error, server error, empty state, and loading state.
3. No rabbit holes section
Bad: Spec that describes what to build but not what to avoid.
Good: "Don't rebuild the notification system for this - use existing email infrastructure."
4. Spec approved with open questions
Bad: "TBD" items in an approved spec.
Good: All open questions resolved or explicitly deferred with a named owner and date.
Quality Checklist