specification-writing

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]

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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

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Writing for Agent Implementers

When an agent reads your spec, they should:

1. Understand the problem from Motivation section
2. Know what's been explored from Research Findings
3. See the proposed direction from Design Decisions
4. Have a starting point from Implementation Plan Phase 1
5. 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.

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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.