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Specification Writing
Follow writing-voice for prose sections.
A specification gives an agent (or human) the context they need to implement a feature autonomously. The goal is NOT to describe everything exhaustively; it's to provide enough initial context that the implementer can do their own research and make informed decisions.
Note : This guide uses [PLACEHOLDER] markers for content you must fill in. Code blocks show templates; replace all bracketed content with your feature's details.
When to Apply This Skill
Use this pattern when you need to:
- Plan a feature with a spec that enables autonomous implementation.
- Document research findings, trade-offs, and design rationale.
- Define phased implementation tasks with trackable checkboxes.
- Capture open questions and recommendations without over-prescribing.
- Lay out architecture with tables/diagrams instead of wall-of-prose plans.
The Core Philosophy
Specs should:
- Provide context, not instructions : Give the "why" and "what", let the implementer figure out "how"
- Document research, not conclusions : Show what was explored, what exists, what doesn't
- Leave questions open : The Open Questions section is a feature, not a bug
- Enable autonomous implementation : An agent reading this should spawn sub-agents to verify and extend
A good spec is a launching pad, not a script to follow.
Document Structure
Header (Required)
# [Feature Name]
**Date**: [YYYY-MM-DD]
**Status**: Draft | In Progress | Implemented
**Author**: [Name or AI-assisted]
**Branch**: [optional: feat/feature-name if work has started]
Overview
One paragraph max. Describe what the feature does. Don't sell it.
## Overview
[One to two sentences describing what this feature adds or changes and what it enables. Be specific about the capability, not vague about benefits.]
Motivation
Structure as Current State → Problems → Desired State.
## Motivation
### Current State
[Show actual code or configuration demonstrating how things work TODAY. Use real code blocks, not prose descriptions.]
This creates problems:
1. **[Problem Title]**: [Specific explanation of what breaks or is painful]
2. **[Problem Title]**: [Specific explanation of what breaks or is painful]
### Desired State
[Brief description of what the target looks like. Can include a code snippet showing the ideal API or structure.]
Research Findings
This is where specs shine. Document what you FOUND, not what you assumed.
## Research Findings
### [Topic Researched]
[Description of what you investigated and methodology]
| [Category] | [Dimension 1] | [Dimension 2] |
| ------------- | -------------- | ---------------- |
| [Project/Lib] | [What they do] | [Their approach] |
| [Project/Lib] | [What they do] | [Their approach] |
**Key finding**: [Your main discovery—could be that no standard exists, or that everyone does X]
**Implication**: [What this means for your design decisions]
Include:
- What similar projects do (comparison tables)
- What you searched for but didn't find ("No Established Pattern Exists")
- Links or references to documentation you consulted
Design Decisions
Use a table for traceability. Every decision should have a rationale.
## Design Decisions
| Decision | Choice | Rationale |
| ------------------- | ---------------- | ------------------------------- |
| [Decision point] | [What you chose] | [Why this over alternatives] |
| [Decision point] | [What you chose] | [Why this over alternatives] |
| [Deferred decision] | Deferred | [Why it's out of scope for now] |
Architecture
Diagrams over prose. Show relationships visually with ASCII art.
## Architecture
[Describe what the diagram shows]
┌─────────────────────────────────────────┐ │ [Component Name] │ │ ├── [field]: [type or value] │ │ └── [field]: [type or value] │ └─────────────────────────────────────────┘ │ ▼ [relationship label] ┌─────────────────────────────────────────┐ │ [Component Name] │ └─────────────────────────────────────────┘
For multi-step flows:
STEP 1: [Step name] ──────────────────── [What happens in this step]
STEP 2: [Step name] ──────────────────── [What happens in this step]
Implementation Plan
Break into phases. Use checkboxes for tracking. Phase 1 should be detailed; later phases can be rougher (the implementer will flesh them out).
## Implementation Plan
### Phase 1: [Phase Name]
- [ ] **1.1** [Specific, atomic task]
- [ ] **1.2** [Specific, atomic task]
- [ ] **1.3** [Specific, atomic task]
### Phase 2: [Phase Name]
- [ ] **2.1** [Higher-level task—implementer will break down]
- [ ] **2.2** [Higher-level task]
Edge Cases
List scenarios that might break assumptions or need special handling.
## Edge Cases
### [Scenario Name]
1. [Initial condition]
2. [What happens]
3. [Expected outcome or "See Open Questions"]
### [Scenario Name]
1. [Initial condition]
2. [What happens]
3. [Expected outcome]
Open Questions
This section signals "you decide this" to the implementer. Include your recommendation but don't close the question.
## Open Questions
1. **[Question about an unresolved design decision]**
- Options: (a) [Option A], (b) [Option B], (c) [Option C]
- **Recommendation**: [Your suggestion and why, but explicitly leave it open]
2. **[Another unresolved question]**
- [Context about why this is uncertain]
- **Recommendation**: [Suggestion or "Defer until X"]
Success Criteria
How do we know this is done? Checkboxes for verification.
## Success Criteria
- [ ] [Specific, verifiable outcome]
- [ ] [Specific, verifiable outcome]
- [ ] [Tests pass / build succeeds / docs updated]
References
Files that will be touched or consulted.
## References
- `[path/to/file.ts]` - [Why this file is relevant]
- `[path/to/pattern.ts]` - [Pattern to follow or reference]
Good vs Bad Specs
Good Spec Characteristics
- Research is documented : Shows what was explored, not just conclusions
- Decisions have rationale : Every choice has a "why" in a table
- Questions are left open : Implementer has room to decide
- Code shows current state : Not described abstractly
- Architecture is visual : ASCII diagrams over prose
- Phases are actionable : Checkboxes that can be tracked
Bad Spec Characteristics
- Prescriptive step-by-step : Reads like a tutorial, no room for autonomy
- Assumes without research : "We'll use X" without exploring alternatives
- Closes all questions : No Open Questions section
- Abstract descriptions : "The system will handle Y" without showing code
- Wall of prose : No tables, no diagrams, no structure
Writing for Agent Implementers
When an agent reads your spec, they should:
- Understand the problem from Motivation section
- Know what's been explored from Research Findings
- See the proposed direction from Design Decisions
- Have a starting point from Implementation Plan Phase 1
- Know what to investigate further from Open Questions
The agent will then:
- Spawn sub-agents to verify your research
- Explore the Open Questions you left
- Flesh out later phases of the implementation plan
- Make decisions where you left room
If your spec is too prescriptive, the agent will blindly follow it. If it's too vague, the agent will flounder. The sweet spot is: enough context to start, enough openness to own the implementation.
Quick Reference Checklist
- [ ] Header (Date, Status, Author)
- [ ] Overview (1-2 sentences)
- [ ] Motivation
- [ ] Current State (with code)
- [ ] Problems (numbered)
- [ ] Desired State
- [ ] Research Findings
- [ ] Comparison tables
- [ ] Key findings
- [ ] Implications
- [ ] Design Decisions (table with rationale)
- [ ] Architecture (ASCII diagrams)
- [ ] Implementation Plan (phased checkboxes)
- [ ] Edge Cases
- [ ] Open Questions (with recommendations)
- [ ] Success Criteria
- [ ] References
Not every spec needs every section. A small feature might skip Research Findings. A migration spec might focus heavily on Edge Cases. Use judgment.
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