1.3 Install SDD Workflow

The Spec-Driven Development (SDD) workflow is the core methodology you'll use throughout this program. In this section, you'll install SDD as an agent skill in Claude Code so a single workflow entry point can route you through the right SDD phase.

What is the SDD Workflow?

SDD is a four-phase process that transforms AI-assisted development from unpredictable "prompt alchemy" into reliable, evidence-based engineering:

Phase	Purpose	Natural-language invocation
1	Transform a feature idea into a detailed specification	Start SDD for a new feature
2	Break the spec into actionable tasks with proof artifacts	Continue SDD with task planning
3	Execute tasks with checkpoints and evidence collection	Continue SDD with implementation
4	Verify implementation matches the specification	Continue SDD with validation

The older slash-command install exposed four separate /SDD-* commands. Forge now uses the recommended skill install instead: one sdd skill reassesses the repository state, loads the right phase instructions, and continues from artifacts already stored in docs/specs/.

Migrating from the old prompt install?

If you previously installed SDD with slash-man generate and still see /SDD-* commands, follow the SDD prompt-to-skill migration guide after verifying the sdd skill works.

Install the SDD Skill

Skills are installed using the skills.sh CLI. Install the SDD skill from the official workflow repository for Claude Code:

npx skills add liatrio-labs/spec-driven-workflow --skill sdd -a claude-code

This command:

1. Fetches the sdd skill from the official Spec-Driven Workflow repository
2. Installs the skill for Claude Code
3. Makes the skill available as a reusable workflow capability instead of four separate custom prompts

You should see output indicating that the sdd skill was installed.

Non-interactive install

If you are scripting setup or want to accept installer prompts automatically, add --yes:

npx skills add liatrio-labs/spec-driven-workflow --skill sdd -a claude-code --yes

Update the SDD Skill

If you already installed the sdd skill and want the latest published version, run:

npx skills update sdd --yes

Restart Claude Code after updating so it reloads the refreshed skill files.

Verify Installation

Restart Claude Code so it loads newly installed skills:

claude

Inside Claude Code, list installed skills:

/skills

You should see sdd in the skill list.

Then invoke the skill using the syntax your agent supports. In Claude Code, use /sdd:

/sdd Start SDD for a new feature in this repository.

Claude should identify the current SDD phase and explain what it needs next. When a phase finishes, the skill gives you the next natural-language request to continue the workflow.

Understanding the Skill

The SDD skill includes:

State-based phase routing

The skill reassesses the repository each time you invoke it. It looks for SDD artifacts under docs/specs/ and routes to the next appropriate phase instead of requiring you to remember which command to run.

Context verification markers

Each phase still uses a marker so you can detect context rot:

• SDD1️⃣ for Spec Generation
• SDD2️⃣ for Task List Generation
• SDD3️⃣ for Task Management
• SDD4️⃣ for Validation

Why? These markers help you detect when Claude starts losing track of the active SDD instructions. If the marker disappears from responses, start a fresh session and re-invoke /sdd with the current repo context.

Structured output

The workflow produces predictable, reviewable artifacts:

• Specifications in docs/specs/[NN]-spec-[feature-name]/
• Task lists with proof artifact definitions
• Validation reports with coverage matrices

Progressive disclosure

SDD includes explicit "stop and wait" gates:

• Questions files before writing specs
• Parent tasks before sub-tasks
• Checkpoint confirmations during execution

This prevents Claude from racing ahead with assumptions.

Where Are Skills Stored?

The skills installer places skills in the target agent's skill directory. The exact location can vary by agent and installer options, so verify through Claude Code rather than depending on a filesystem path:

/skills

For current install options, use the Spec-Driven Workflow README quickstart as the source of truth.

Slash Commands Are a Fallback

The Spec-Driven Workflow repository still supports slash-command prompts for assistants that do not support skills or teams that specifically want separate phase commands. Forge participants should use the skill path above unless a facilitator tells them otherwise.

Troubleshooting

npx: command not found

Ensure Node.js and npm are installed, then check:

node --version
npm --version
npx --version

Return to the environment setup section if these commands are unavailable.

Skill does not appear in Claude Code

1. Restart Claude Code completely

2. Run /skills again

3. Re-run the install command with --yes

4. If the installer reports permission or symlink errors, retry with --copy:

   npx skills add liatrio-labs/spec-driven-workflow --skill sdd -a claude-code --copy

Network errors during installation

The command fetches from GitHub. Ensure you have internet access and can reach github.com.

Next Steps

With the SDD workflow installed as a skill, the next section covers setting up MCP servers and additional skills that extend Claude's capabilities beyond code generation.

Knowledge Check

Question 1 of 5

Install SDD Workflow Knowledge Check

Q1. Place the four SDD workflow phases in the correct order.

• 1.Generate a detailed specification from a feature idea
• 2.Verify implementation matches the specification
• 3.Break the spec into actionable tasks with proof artifacts
• 4.Execute tasks with checkpoints and evidence collection