OpenSpec Skill

Spec-driven development workflow using the openspec CLI.

Quick Checklist

• Search existing work: openspec spec list --long, openspec list
• Decide scope: new capability vs modify existing
• Pick unique change-id: kebab-case, verb-led (add-, update-, remove-, refactor-)
• Scaffold: proposal.md, tasks.md, design.md (if needed), delta specs per capability
• Write deltas: ## ADDED|MODIFIED|REMOVED|RENAMED Requirements; ≥1 #### Scenario: per requirement
• Validate: openspec validate [change-id] --strict
• Request approval before implementation

Three-Stage Workflow

Stage 1: Creating Changes

Create proposal for:

• New features/functionality
• Breaking changes (API, schema)
• Architecture changes
• Performance optimizations
• Security pattern updates

Skip proposal for:

• Bug fixes (restore intended behavior)
• Typos, formatting, comments
• Non-breaking dependency updates
• Configuration changes
• Tests for existing behavior

Workflow:

1. Review openspec/project.md, openspec list, openspec list --specs
2. Choose verb-led change-id, scaffold under openspec/changes/<id>/
3. Draft spec deltas with ## ADDED|MODIFIED|REMOVED Requirements
4. Run openspec validate <id> --strict

Stage 2: Implementing Changes

1. Read proposal.md
2. Read design.md (if exists)
3. Read tasks.md
4. Implement tasks sequentially
5. Confirm all tasks complete
6. Update checklist to - [x]
7. Do not start until proposal approved

Stage 3: Archiving Changes

After deployment:

• Move changes/[name]/ → changes/archive/YYYY-MM-DD-[name]/
• Update specs/ if capabilities changed
• Use openspec archive <change-id> --skip-specs --yes for tooling-only changes
• Run openspec validate --strict

Before Any Task

Context Checklist:

• Read relevant specs in specs/[capability]/spec.md
• Check pending changes in changes/ for conflicts
• Read openspec/project.md for conventions
• Run openspec list to see active changes
• Run openspec list --specs to see existing capabilities

Before Creating Specs:

• Check if capability already exists
• Prefer modifying existing specs over duplicates
• Use openspec show [spec] to review current state
• Ask 1–2 clarifying questions if ambiguous

CLI Commands

# Essential
openspec list                  # List active changes
openspec list --specs          # List specifications
openspec show [item]           # Display change or spec
openspec validate [item]       # Validate changes or specs
openspec archive <change-id> [--yes|-y]   # Archive after deployment

# Project management
openspec init [path]           # Initialize OpenSpec
openspec update [path]         # Update instruction files

# Debugging
openspec show [change] --json --deltas-only
openspec validate [change] --strict

Flags: --json, --type change|spec, --strict, --no-interactive, --skip-specs, --yes/-y

Directory Structure

openspec/
├── project.md              # Project conventions
├── specs/                  # Current truth - what IS built
│   └── [capability]/
│       ├── spec.md         # Requirements and scenarios
│       └── design.md       # Technical patterns
├── changes/                # Proposals - what SHOULD change
│   ├── [change-name]/
│   │   ├── proposal.md     # Why, what, impact
│   │   ├── tasks.md        # Implementation checklist
│   │   ├── design.md       # Technical decisions (optional)
│   │   └── specs/          # Delta changes
│   │       └── [capability]/
│   │           └── spec.md # ADDED/MODIFIED/REMOVED
│   └── archive/            # Completed changes

Creating Change Proposals

Decision Tree

New request?
├─ Bug fix restoring spec behavior? → Fix directly
├─ Typo/format/comment? → Fix directly
├─ New feature/capability? → Create proposal
├─ Breaking change? → Create proposal
├─ Architecture change? → Create proposal
└─ Unclear? → Create proposal (safer)

proposal.md Template

# Change: [Brief description]

## Why
[1-2 sentences on problem/opportunity]

## What Changes
- [Bullet list]
- [Mark breaking changes with **BREAKING**]

## Impact
- Affected specs: [list capabilities]
- Affected code: [key files/systems]

Spec Delta Template

## ADDED Requirements

### Requirement: New Feature
The system SHALL provide...

#### Scenario: Success case
- **WHEN** user performs action
- **THEN** expected result

## MODIFIED Requirements

### Requirement: Existing Feature
[Complete modified requirement]

## REMOVED Requirements

### Requirement: Old Feature
**Reason**: [Why removing]
**Migration**: [How to handle]

tasks.md Template

## 1. Implementation
- [ ] 1.1 Create database schema
- [ ] 1.2 Implement API endpoint
- [ ] 1.3 Add frontend component
- [ ] 1.4 Write tests

design.md (When Needed)

Create if any apply:

• Cross-cutting change or new architectural pattern
• New external dependency or significant data model changes
• Security, performance, or migration complexity
• Ambiguity benefiting from technical decisions

## Context
[Background, constraints, stakeholders]

## Goals / Non-Goals
- Goals: [...]
- Non-Goals: [...]

## Decisions
- Decision: [What and why]
- Alternatives considered: [Options + rationale]

## Risks / Trade-offs
- [Risk] → Mitigation

## Migration Plan
[Steps, rollback]

## Open Questions
- [...]

Spec File Format

Critical: Scenario Formatting

CORRECT (use #### headers):

#### Scenario: User login success
- **WHEN** valid credentials provided
- **THEN** return JWT token

WRONG:

- **Scenario: User login** ❌
  **Scenario**: User login ❌
### Scenario: User login ❌

Every requirement MUST have at least one scenario.

Requirement Wording

Use SHALL/MUST for normative requirements.

Delta Operations

• ## ADDED Requirements - New capabilities
• ## MODIFIED Requirements - Changed behavior
• ## REMOVED Requirements - Deprecated features
• ## RENAMED Requirements - Name changes

ADDED vs MODIFIED

• ADDED: New capability that stands alone
• MODIFIED: Changes behavior of existing requirement. Always paste full updated requirement (header + scenarios)
• RENAMED: Only name changes. If also changing behavior, use RENAMED + MODIFIED

Common pitfall: Using MODIFIED without including previous text causes loss of detail at archive time.

Authoring MODIFIED correctly:

1. Locate existing requirement in openspec/specs/<capability>/spec.md
2. Copy entire requirement block
3. Paste under ## MODIFIED Requirements and edit
4. Ensure header matches exactly, keep ≥1 scenario

Troubleshooting

"Change must have at least one delta"

• Check changes/[name]/specs/ exists with .md files
• Verify files have ## ADDED Requirements etc.

"Requirement must have at least one scenario"

• Use #### Scenario: format (4 hashtags)
• Don't use bullets or bold for scenario headers

Silent scenario parsing failures

• Exact format: #### Scenario: Name
• Debug: openspec show [change] --json --deltas-only

Happy Path Script

# 1) Explore current state
openspec spec list --long
openspec list

# 2) Scaffold
CHANGE=add-two-factor-auth
mkdir -p openspec/changes/$CHANGE/{specs/auth}
printf "## Why\n...\n\n## What Changes\n- ...\n\n## Impact\n- ...\n" > openspec/changes/$CHANGE/proposal.md
printf "## 1. Implementation\n- [ ] 1.1 ...\n" > openspec/changes/$CHANGE/tasks.md

# 3) Add deltas
cat > openspec/changes/$CHANGE/specs/auth/spec.md << 'EOF'
## ADDED Requirements
### Requirement: Two-Factor Authentication
Users MUST provide a second factor during login.

#### Scenario: OTP required
- **WHEN** valid credentials are provided
- **THEN** an OTP challenge is required
EOF

# 4) Validate
openspec validate $CHANGE --strict

Best Practices

Naming

Capabilities: verb-noun (user-auth, payment-capture), single purpose, split if needs "AND"

Change IDs: kebab-case, verb-led (add-, update-, remove-, refactor-), unique

Simplicity First

• Default to <100 lines of new code
• Single-file implementations until proven insufficient
• Avoid frameworks without clear justification

Clear References

• Use file.ts:42 for code locations
• Reference specs as specs/auth/spec.md

Quick Reference

Stage Indicators:

• changes/ - Proposed, not yet built
• specs/ - Built and deployed
• archive/ - Completed changes

File Purposes:

• proposal.md - Why and what
• tasks.md - Implementation steps
• design.md - Technical decisions
• spec.md - Requirements and behavior

CLI Essentials:

openspec list              # What's in progress?
openspec show [item]       # View details
openspec validate --strict # Is it correct?
openspec archive <change-id> --yes  # Mark complete

Specs are truth. Changes are proposals. Keep them in sync.