Codex SDD Loop

Spec-driven development for Codex. Turn feature requests into proposals, specs, tasks, validation evidence, and archived engineering knowledge.

What is Codex SDD Loop?

Codex SDD Loop is a Codex plugin that brings the OpenSpec development loop into everyday AI-assisted engineering. Instead of jumping directly from a prompt to code, it keeps every change inside a traceable workflow:

1. Propose - clarify scope, background, out-of-scope work, and acceptance criteria.
2. Plan - generate specs, design notes, task lists, verification plans, and implementation notes.
3. Implement - work through tasks with durable progress tracking.
4. Validate - check artifacts, task completion, hooks, and spec-vs-code drift.
5. Archive - preserve the finished change and accumulate project knowledge.

The plugin is built around Codex skills plus a local MCP server. Skills guide the agent's behavior; the MCP server creates files, maintains workflow state, validates changes, and exposes status/continuation tools.

Why use it?

• Human gates where they matter - review scope, design, validation, and archive readiness before the workflow advances.
• Resumable work - interrupted sessions can continue from .openspec-codex/state.json without re-explaining the change.
• Change-scoped artifacts - every feature or fix lives under openspec/changes/<changeId>/.
• Custom team process - project config, schemas, templates, rules, and hooks can be adapted to your engineering workflow.
• Audit-friendly output - proposals, specs, tasks, verification evidence, and archives stay in your repository.

Quick Start

Prerequisites

• Codex desktop app with local plugin support
• Node.js 18 or newer
• npm 9 or newer

Install from GitHub

git clone https://github.com/skyloevil/codex-sdd-loop.git
cd codex-sdd-loop
npm install --prefix mcp-server
npm run build --prefix mcp-server

Then install the plugin in Codex:

1. Open Codex Settings.
2. Go to Plugins.
3. Choose Add from folder.
4. Select the cloned codex-sdd-loop directory.

The plugin manifest is in .codex-plugin/plugin.json, and the MCP server configuration is in .mcp.json.

Basic Usage

Start with a request in Codex:

Use Codex SDD Loop to propose: Add user avatar upload

The workflow creates a change directory like this:

openspec/changes/add-user-avatar-upload-20260627/
  proposal.md
  specs/spec.md
  design.md
  tasks.md
  verification.md
  implementation-notes.md

After the proposal is reviewed, continue the flow:

Use Codex SDD Loop to plan this change
Use Codex SDD Loop to implement the next task
Use Codex SDD Loop to validate the current change
Use Codex SDD Loop to archive the completed change

You can also recover context at any point:

Use Codex SDD Loop to show status
Use Codex SDD Loop to continue

Optional TAPD Requirement Import

Codex SDD Loop includes an optional tapd-requirement MCP adapter that can fetch a TAPD story before proposal generation. This is useful when the source requirement lives in TAPD and the Codex prompt only contains a story URL.

Before using TAPD import, configure your TAPD API account and password in your local environment. Do not commit real credentials to this repository.

For local terminal testing, you can create a private .tapd.env.local file:

TAPD_API_USER=your_tapd_api_user
TAPD_API_PASSWORD=your_tapd_api_password

.tapd.env.local is ignored by git. For Codex plugin usage, provide the same variables through your shell environment, personal Codex MCP configuration, or another local secret mechanism available to your Codex runtime.

The bundled TAPD MCP adapter also attempts to load .tapd.env.local from the current project root and from the Codex SDD Loop plugin root. If another project cannot see tapd-requirement:fetch_story, reload Codex MCP servers after updating the plugin and confirm that the plugin MCP server is exposed in that session. If the tool is visible but fails with missing credentials, the MCP process cannot see TAPD_API_USER or TAPD_API_PASSWORD.

The plugin MCP configuration uses plugin-root-relative commands (cwd: "." with ./... paths), so the OpenSpec and TAPD MCP tools are available from any project directory once the plugin is installed and MCP servers are reloaded.

After reloading Codex MCP servers, trigger proposal generation with a TAPD story URL:

Use Codex SDD Loop to propose https://www.tapd.cn/tapd_fe/<workspace_id>/story/detail/<story_id>

The TAPD adapter parses the URL, calls the TAPD stories API, and returns normalized proposalInput fields for the OpenSpec proposal workflow. The raw TAPD API response is also included for custom field inspection.

Commands and Skills

Codex SDD Loop ships with focused Codex skills:

MCP Tools

The MCP server exposes structured tools used by the skills and by Codex:

Workflow

flowchart LR
    A["Requirement"] --> B["Propose"]
    B --> C{"Scope approved?"}
    C -->|Yes| D["Plan"]
    C -->|No| B
    D --> E{"Design approved?"}
    E -->|Yes| F["Implement"]
    E -->|No| D
    F --> G["Validate"]
    G --> H{"Checks pass?"}
    H -->|No| F
    H -->|Yes| I["Archive"]
    I --> J["Knowledge Base"]

State Model

Workflow state is stored in .openspec-codex/state.json. Version 2 supports multiple tracked changes with one active change:

{
  "version": 2,
  "activeChangeId": "add-user-avatar-upload-20260627",
  "changes": {
    "add-user-avatar-upload-20260627": {
      "phase": "implement",
      "preset": "full",
      "paths": {
        "changeDir": "openspec/changes/add-user-avatar-upload-20260627",
        "proposal": "openspec/changes/add-user-avatar-upload-20260627/proposal.md",
        "tasks": "openspec/changes/add-user-avatar-upload-20260627/tasks.md"
      },
      "gates": {
        "scope": true,
        "design": true,
        "validation": false,
        "archive": false
      },
      "nextAction": "Implement the next incomplete task."
    }
  },
  "updatedAt": "2026-06-27T00:00:00.000Z"
}

This file is intentionally project-local so Codex can resume an interrupted OpenSpec workflow.

Customization

Initialize a project to create the default OpenSpec workspace:

Use Codex SDD Loop to initialize this project

Generated configuration lives in:

openspec/
  config.yaml
  schemas/
    spec-driven/
      schema.yaml
      templates/

You can customize:

• Schemas - choose which artifacts are required for full features, hotfixes, and small tweaks.
• Templates - define team-specific proposal, spec, design, task, verification, and notes formats.
• Rules - require architecture, compatibility, API, persistence, caching, or testing constraints.
• Hooks - call MCP tools, commands, or skills before and after workflow steps.

Example hook configuration:

hooks:
  pre_archive:
    - kind: skill
      name: implementation-notes-backfill
      required: true

Development

Install dependencies:

npm install --prefix mcp-server

Build the MCP server:

npm run build --prefix mcp-server

Run tests:

npm test --prefix mcp-server

Run the server locally:

npm run dev --prefix mcp-server

Project Structure

codex-sdd-loop/
  .codex-plugin/
    plugin.json
  .mcp.json
  assets/
    icon.png
    logo.png
    logo-dark.png
  mcp-server/
    src/
      index.ts
      openspec.ts
      state.ts
      types.ts
    test/
      openspec.test.ts
    package.json
    tsconfig.json
  skills/
    archive/
    continue/
    customize/
    implement/
    plan/
    propose/
    status/
    tapd-openspec-proposal/
    validate/
  scripts/
    tapd-mcp-server.mjs

Relationship to OpenSpec

This project follows the OpenSpec-style workflow and is designed for Codex plugin usage. It is inspired by the structured development loop promoted by Fission-AI/OpenSpec, while focusing on local MCP tools, resumable state, and Codex skills.

Contributing

Contributions are welcome. Please keep changes spec-driven:

1. Open an issue or proposal describing the behavior change.
2. Add or update tests for MCP server behavior when applicable.
3. Run npm test --prefix mcp-server.
4. Keep generated dependencies such as node_modules/ out of commits.

License

Codex SDD Loop is released under the MIT License.