Agent skill

Phase 4 API

Design and implement backend APIs with Zero Script QA validation.

Apache-2.0Auto-check: notesBackend & APIs

Install Phase 4 API

skills CLI

$ npx skills add ww-w-ai/bkit-claude-code --skill phase-4-api -a claude-code

Project install by default; add -g for ~/.claude/skills/.

GitHub CLI

$ gh skill install ww-w-ai/bkit-claude-code phase-4-api --agent claude-code

Project scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).

Manual copy

$ git clone --depth 1 https://github.com/ww-w-ai/bkit-claude-code.git skills-src && mkdir -p .claude/skills && cp -r skills-src/skills/phase-4-api .claude/skills/phase-4-api && rm -rf skills-src

Use ~/.claude/skills/ instead of .claude/skills for a personal install. The folder must contain SKILL.md.

Claude Code skills documentation · loads skills from .claude/skills/

Paste into Claude Code

Install the "phase-4-api" agent skill from https://github.com/ww-w-ai/bkit-claude-code/tree/main/skills/phase-4-api into .claude/skills/phase-4-api/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "phase-4-api", then confirm the skill loads.

Claude Code copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

$skill-installer

$skill-installer install https://github.com/ww-w-ai/bkit-claude-code/tree/main/skills/phase-4-api

Type this inside Codex. $skill-installer <name> installs a curated skill from openai/skills. The installer writes to $CODEX_HOME/skills (default ~/.codex/skills). Restart Codex if the skill does not show up.

skills CLI

$ npx skills add ww-w-ai/bkit-claude-code --skill phase-4-api -a codex

Project install goes to .agents/skills/; add -g for ~/.codex/skills/.

GitHub CLI

$ gh skill install ww-w-ai/bkit-claude-code phase-4-api --agent codex

Project scope by default (.agents/skills/); add --scope user for a personal install.

Manual copy

$ git clone --depth 1 https://github.com/ww-w-ai/bkit-claude-code.git skills-src && mkdir -p .agents/skills && cp -r skills-src/skills/phase-4-api .agents/skills/phase-4-api && rm -rf skills-src

Use ~/.agents/skills/ instead of .agents/skills for a personal install.

Codex skills documentation · loads skills from .agents/skills/

Paste into Codex

Install the "phase-4-api" agent skill from https://github.com/ww-w-ai/bkit-claude-code/tree/main/skills/phase-4-api into .agents/skills/phase-4-api/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "phase-4-api", then confirm the skill loads.

Codex copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

skills CLI

$ npx skills add ww-w-ai/bkit-claude-code --skill phase-4-api -a cursor

Project install goes to .agents/skills/; add -g for ~/.cursor/skills/.

GitHub CLI

$ gh skill install ww-w-ai/bkit-claude-code phase-4-api --agent cursor

Project scope by default (.agents/skills/); add --scope user for a personal install.

Manual copy

$ git clone --depth 1 https://github.com/ww-w-ai/bkit-claude-code.git skills-src && mkdir -p .cursor/skills && cp -r skills-src/skills/phase-4-api .cursor/skills/phase-4-api && rm -rf skills-src

Use ~/.cursor/skills/ instead of .cursor/skills for a personal install.

Cursor skills documentation · loads skills from .cursor/skills/, .agents/skills/, .claude/skills/, .codex/skills/

Paste into Cursor

Install the "phase-4-api" agent skill from https://github.com/ww-w-ai/bkit-claude-code/tree/main/skills/phase-4-api into .cursor/skills/phase-4-api/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "phase-4-api", then confirm the skill loads.

Cursor copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

gemini skills install

$ gemini skills install https://github.com/ww-w-ai/bkit-claude-code.git --path skills/phase-4-api

--scope user (default) or --scope workspace; --path is the subfolder of the repo that holds the skill; --consent skips the security confirmation prompt.

skills CLI

$ npx skills add ww-w-ai/bkit-claude-code --skill phase-4-api -a gemini-cli

Project install goes to .agents/skills/; add -g for ~/.gemini/skills/.

GitHub CLI

$ gh skill install ww-w-ai/bkit-claude-code phase-4-api --agent gemini-cli

Project scope by default (.agents/skills/); add --scope user for a personal install.

Manual copy

$ git clone --depth 1 https://github.com/ww-w-ai/bkit-claude-code.git skills-src && mkdir -p .gemini/skills && cp -r skills-src/skills/phase-4-api .gemini/skills/phase-4-api && rm -rf skills-src

Use ~/.gemini/skills/ instead of .gemini/skills for a personal install, then run /skills reload.

Gemini CLI skills documentation · loads skills from .gemini/skills/, .agents/skills/

Paste into Gemini CLI

Install the "phase-4-api" agent skill from https://github.com/ww-w-ai/bkit-claude-code/tree/main/skills/phase-4-api into .gemini/skills/phase-4-api/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "phase-4-api", then confirm the skill loads.

Gemini CLI copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

GitHub CLI

$ gh skill install ww-w-ai/bkit-claude-code phase-4-api

Installs for Copilot at project scope by default; add --scope user for a personal install. Preview a skill first with gh skill preview. Needs GitHub CLI 2.90.0 or later (public preview).

skills CLI

$ npx skills add ww-w-ai/bkit-claude-code --skill phase-4-api -a github-copilot

Project install goes to .agents/skills/; add -g for ~/.copilot/skills/.

Manual copy

$ git clone --depth 1 https://github.com/ww-w-ai/bkit-claude-code.git skills-src && mkdir -p .github/skills && cp -r skills-src/skills/phase-4-api .github/skills/phase-4-api && rm -rf skills-src

Use ~/.copilot/skills/ instead of .github/skills for a personal install. Commit .github/skills so cloud agent and code review can use it.

GitHub Copilot skills documentation · loads skills from .github/skills/, .claude/skills/, .agents/skills/

Paste into GitHub Copilot

Install the "phase-4-api" agent skill from https://github.com/ww-w-ai/bkit-claude-code/tree/main/skills/phase-4-api into .github/skills/phase-4-api/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "phase-4-api", then confirm the skill loads.

GitHub Copilot copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

skills CLI

$ npx skills add ww-w-ai/bkit-claude-code --skill phase-4-api -a opencode

OpenCode documents no install command of its own. Project install goes to .agents/skills/; add -g for ~/.config/opencode/skills/.

GitHub CLI

$ gh skill install ww-w-ai/bkit-claude-code phase-4-api --agent opencode

Project scope by default (.agents/skills/); add --scope user for a personal install.

Manual copy

$ git clone --depth 1 https://github.com/ww-w-ai/bkit-claude-code.git skills-src && mkdir -p .opencode/skills && cp -r skills-src/skills/phase-4-api .opencode/skills/phase-4-api && rm -rf skills-src

Use ~/.config/opencode/skills/ instead of .opencode/skills for a personal install.

OpenCode skills documentation · loads skills from .opencode/skills/, .claude/skills/, .agents/skills/

Paste into OpenCode

Install the "phase-4-api" agent skill from https://github.com/ww-w-ai/bkit-claude-code/tree/main/skills/phase-4-api into .opencode/skills/phase-4-api/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "phase-4-api", then confirm the skill loads.

OpenCode copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.

Facts

Skill name: phase-4-api
GitHub stars: 601
Token cost: ~1.8k tokens
SKILL.md length: 425 words
Files: 1
Skills in repo: 44
Repo updated: Sep 27, 2026
First seen: Oct 7, 2026
Licence: Apache-2.0

At a glance

Design and implement backend APIs with Zero Script QA validation.

Tasks that involve API design
SKILL.md covers Purpose, What to Do in This Phase, Deliverables and PDCA Application, plus 6 more sections
Calls claude; reaches api.bkend.ai
Tasks that involve REST APIs

What it does

Phase 4 API is an agent skill from ww-w-ai/bkit-claude-code. Design and implement backend APIs with Zero Script QA validation. Triggers: API design, REST API, backend, endpoint

Its SKILL.md is about 1.8k tokens, which your agent loads only when the skill is triggered. It is a single SKILL.md file with no bundled scripts.

It sits in Backend & APIs, covering API design and REST APIs. The repository describes itself as: bkit Vibecoding Kit - PDCA methodology + Claude Code mastery for AI-native development. The licence is Apache-2.0.

When your agent uses it

Tasks that involve API design
Tasks that involve REST APIs

Example prompts

“/phase-4-api”

Requirements

Pre-approved tools (allowed-tools): Read, Write, Edit, Glob, Grep, Bash

What it can do on your machine

Read from SKILL.md and the folder at commit 85b4913. It shows what the files ask for, not the result of running them.

Tool permissions
Pre-approves these tools, so the agent can use them without asking each time:
- Read
- Write
- Edit
- Glob
- Grep
- Bash
From allowed-tools in the SKILL.md frontmatter.
Runs code
Shell commands in SKILL.md call:
- claude
From the folder's file list and the shell code blocks in SKILL.md.
Network
Hosts in commands or code, which the agent is likely to contact:
- api.bkend.ai
From URLs in SKILL.md, links to its own repository left out.
Credentials
Names no API keys, tokens, secrets or passwords.
From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

Phase 4 API loads about 1.8k tokens when it runs. Until then it costs about 32 tokens; SKILL.md has 425 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it: ~32
When it runs · the whole SKILL.md, loaded when a task matches: ~1.8k

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Auto-check: notes

The automated check noted patterns worth knowing about, such as sudo or a known installer.

NotePre-approves every shell command (allowed-tools: Bash)SKILL.md
```
allowed-tools: Read, Write, Edit, Glob, Grep, Bash
```

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

The full file from ww-w-ai/bkit-claude-code at commit 85b4913, republished under its Apache-2.0 licence (© ww-w-ai). 425 words, ~1,764 tokens.

Download SKILL.mdSave it as .claude/skills/phase-4-api/SKILL.md (or your agent's skills folder).

name: phase-4-api
description: Design and implement backend APIs with Zero Script QA validation. Triggers: API design, REST API, backend, endpoint
allowed-tools: Read, Write, Edit, Glob, Grep, Bash
context: fork
background: false
classification: capability
classification-reason: Pattern guidance may overlap with model's built-in knowledge as it improves
deprecation-risk: medium
effort: high
user-invocable: false
agent: bkit:qa-monitor
next-skill: phase-5-design-system
pdca-phase: do

Phase 4: API Design/Implementation + Zero Script QA

Backend API implementation and script-free QA

Purpose

Implement backend APIs that can store and retrieve data. Validate with structured logs instead of test scripts.

What to Do in This Phase

API Design: Define endpoints, requests/responses
API Implementation: Write actual backend code
Zero Script QA: Log-based validation

Deliverables

docs/02-design/
└── api-spec.md             # API specification

src/api/                    # API implementation
├── routes/
├── controllers/
└── services/

docs/03-analysis/
└── api-qa.md               # QA results

PDCA Application

Plan: Define required API list
Design: Design endpoints, requests/responses
Do: Implement APIs
Check: Validate with Zero Script QA
Act: Fix bugs and proceed to Phase 5

Level-wise Application

Level	Application Method
Starter	Skip this Phase (no API)
Dynamic	Use bkend.ai BaaS (see below)
Enterprise	Implement APIs directly

Dynamic Level: bkend.ai BaaS API Implementation

Step 1: MCP Setup

bash

claude mcp add bkend --transport http https://api.bkend.ai/mcp

Step 2: Table Design (via MCP tools)

Natural language request: "Create a users table with name(required), email(required, unique), age fields" -> MCP backend_table_create auto-invoked

Step 3: Service API Integration

Method	Endpoint	Description
GET	/v1/data/{table}	List (filter, sort, page)
POST	/v1/data/{table}	Create data
GET	/v1/data/{table}/{id}	Get single
PATCH	/v1/data/{table}/{id}	Partial update
DELETE	/v1/data/{table}/{id}	Delete

Required Headers: x-project-id, x-environment, Authorization

Step 4: Auth Implementation

Reference MCP tools 3_howto_implement_auth and 6_code_examples_auth

Step 5: Zero Script QA

Check bkend REST API call logs in browser DevTools Network tab
Verify API behavior via response code/body

What is Zero Script QA?

Instead of writing test scripts, validate with structured debug logs

[API] POST /api/users
[INPUT] { "email": "test@test.com", "name": "Test" }
[PROCESS] Email duplicate check → Passed
[PROCESS] Password hash → Complete
[PROCESS] DB save → Success
[OUTPUT] { "id": 1, "email": "test@test.com" }
[RESULT] ✅ Success

Advantages:
- Save test code writing time
- See actual behavior with your eyes
- Easy debugging

RESTful API Principles

What is REST?

REpresentational State Transfer - an architecture style for designing web services.

Show full SKILL.md (199 more words)Show less

6 Core Principles

Principle	Description	Example
1. Client-Server	Separation of concerns between client and server	UI ↔ Data storage separated
2. Stateless	Each request is independent, server doesn't store client state	Auth token included with each request
3. Cacheable	Responses must indicate if cacheable	`Cache-Control` header
4. Uniform Interface	Interact through consistent interface	Detailed below
5. Layered System	Allow layered system architecture	Load balancer, proxy
6. Code on Demand	(Optional) Server can send code to client	JavaScript delivery

Uniform Interface Details

The core of RESTful APIs is a uniform interface.

1. Resource-Based URLs

✅ Good (nouns, plural)
GET    /users          # User list
GET    /users/123      # Specific user
POST   /users          # Create user
PUT    /users/123      # Update user
DELETE /users/123      # Delete user

❌ Bad (using verbs)
GET    /getUsers
POST   /createUser
POST   /deleteUser/123

2. HTTP Method Meanings

Method	Purpose	Idempotent	Safe
`GET`	Read	✅	✅
`POST`	Create	❌	❌
`PUT`	Full update	✅	❌
`PATCH`	Partial update	❌	❌
`DELETE`	Delete	✅	❌

Idempotent: Same result even if requested multiple times Safe: Doesn't change server state

3. HTTP Status Codes

2xx Success
├── 200 OK              # Success (read, update)
├── 201 Created         # Creation success
└── 204 No Content      # Success but no response body (delete)

4xx Client Error
├── 400 Bad Request     # Invalid request (validation failure)
├── 401 Unauthorized    # Authentication required
├── 403 Forbidden       # No permission
├── 404 Not Found       # Resource not found
└── 409 Conflict        # Conflict (duplicate, etc.)

5xx Server Error
├── 500 Internal Error  # Internal server error
└── 503 Service Unavailable  # Service unavailable

4. Consistent Response Format

json

// Success response
{
  "data": {
    "id": 123,
    "email": "user@example.com",
    "name": "John Doe"
  },
  "meta": {
    "timestamp": "2026-01-08T10:00:00Z"
  }
}

// Error response
{
  "error": {
    "code": "VALIDATION_ERROR",
    "message": "Email format is invalid.",
    "details": [
      { "field": "email", "message": "Please enter a valid email" }
    ]
  }
}

// List response (pagination)
{
  "data": [...],
  "pagination": {
    "page": 1,
    "limit": 20,
    "total": 100,
    "totalPages": 5
  }
}

URL Design Rules

1. Use lowercase
   ✅ /users/123/orders
   ❌ /Users/123/Orders

2. Use hyphens (-), avoid underscores (_)
   ✅ /user-profiles
   ❌ /user_profiles

3. Express hierarchical relationships
   ✅ /users/123/orders/456

4. Filtering via query parameters
   ✅ /users?status=active&sort=created_at
   ❌ /users/active/sort/created_at

5. Version management
   ✅ /api/v1/users
   ✅ Header: Accept: application/vnd.api+json;version=1

API Documentation Tools

Tool	Features
OpenAPI (Swagger)	Industry standard, auto documentation
Postman	Testing + documentation
Insomnia	Lightweight API client

API Design Checklist

RESTful Principles Compliance
- Resource-based URLs (nouns, plural)
- Appropriate HTTP methods
- Correct status codes
Unified error response format
Authentication/authorization method defined
Pagination method defined
Versioning method (optional)

Templates

templates/pipeline/phase-4-api.template.md
templates/pipeline/zero-script-qa.template.md

Next Phase

Phase 5: Design System → APIs are ready, now build UI components

Files

Just SKILL.md in skills/phase-4-api of ww-w-ai/bkit-claude-code.

Open the folder on GitHubat commit 85b4913

Compare with similar skills

Phase 4 API next to the 5 skills that share the most tags, products or categories with it. Stars are the repository's; “used in” counts other GitHub owners with a copy.

Phase 4 API compared with similar skills
Skill	Stars	Used in	Tokens	Auto-check	Licence	Repo updated
Phase 4 API this skillww-w-ai/bkit-claude-code	601	—	~1.8k	Automated safety check: Notes	Apache-2.0	12 days ago
Nodejs Backend Patternsever-works/ever-works	162	18 repos	~4k	Automated safety check: Pass	AGPL-3.0	today
API DesignerJeffallan/claude-skills	12k	1 repos	~2k	Automated safety check: Pass	MIT	6 days ago
Pangolin CRUD Endpointsfosrl/pangolin	23k	—	~461	Automated safety check: Pass	Custom licence	today
Old Coder API DesignAmazingAng/old-coder	749	—	~3.4k	Automated safety check: Pass	MIT	1 mo ago
Backend FundamentalsDanielPodolsky/ownyourcode	290	1 repos	~1.1k	Automated safety check: Pass	MIT	3 mo ago

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Questions about Phase 4 API

What does Phase 4 API do?

Design and implement backend APIs with Zero Script QA validation. Phase 4 API is an agent skill from ww-w-ai/bkit-claude-code. Design and implement backend APIs with Zero Script QA validation.

When should I use Phase 4 API?

Phase 4 API fits situations like: tasks that involve API design; tasks that involve REST APIs.

How do I install Phase 4 API in Claude Code?

Run `npx skills add ww-w-ai/bkit-claude-code --skill phase-4-api -a claude-code`. Or copy the skill folder (skills/phase-4-api in ww-w-ai/bkit-claude-code) into .claude/skills/phase-4-api in your project. Claude Code loads it when a task matches its description.

How do I install Phase 4 API in Codex?

Run `npx skills add ww-w-ai/bkit-claude-code --skill phase-4-api -a codex`. Or copy the skill folder (skills/phase-4-api in ww-w-ai/bkit-claude-code) into .agents/skills/phase-4-api in your project. Codex loads it when a task matches its description.

Can I use Phase 4 API in Cursor, Gemini CLI or GitHub Copilot?

Cursor, Gemini CLI, GitHub Copilot and OpenCode also load SKILL.md folders. With the skills CLI, run `npx skills add ww-w-ai/bkit-claude-code --skill phase-4-api -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/phase-4-api, .gemini/skills/phase-4-api, .github/skills/phase-4-api and .opencode/skills/phase-4-api in your project.

What does Phase 4 API need to run?

Going by SKILL.md and its folder, Phase 4 API needs the command-line tools its instructions call (claude). Its frontmatter pre-approves these tools: Read, Write, Edit, Glob, Grep, Bash.

Does Phase 4 API access the network?

SKILL.md names 1 domain. In commands or code: api.bkend.ai; the agent is likely to contact it when it follows the instructions. This is read from the text; nothing was executed.

Is Phase 4 API safe to install?

Our automated static check of SKILL.md found notes only (pre-approves every shell command (allowed-tools: bash)), nothing it rates as a warning. It is not a guarantee. Review the folder before installing.

What licence does Phase 4 API use?

Phase 4 API is published under the Apache-2.0 licence (the repository's licence). It allows redistribution, so the full SKILL.md is shown on this page.

How many tokens does Phase 4 API use?

About 1.8k tokens (SKILL.md is roughly 7.1k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full.

What are the alternatives to Phase 4 API?

Skills that share tags, products or a category with Phase 4 API: Nodejs Backend Patterns (ever-works/ever-works, 162 stars), API Designer (Jeffallan/claude-skills, 12k stars), Pangolin CRUD Endpoints (fosrl/pangolin, 23k stars) and Old Coder API Design (AmazingAng/old-coder, 749 stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains Phase 4 API?

ww-w-ai (a GitHub organization) maintains it in ww-w-ai/bkit-claude-code, which has 601 GitHub stars. The repository holds 44 skills in this directory. The repository was last updated on September 27, 2026.

Source: ww-w-ai/bkit-claude-code on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.

Install Phase 4 API

Facts

At a glance

What it does

When your agent uses it

Example prompts

Requirements

What it can do on your machine

Tool permissions

Runs code

Network

Credentials

Context cost

Safety

SKILL.md

Phase 4: API Design/Implementation + Zero Script QA

Purpose

What to Do in This Phase

Deliverables

PDCA Application

Level-wise Application

Dynamic Level: bkend.ai BaaS API Implementation

Step 1: MCP Setup

Step 2: Table Design (via MCP tools)

Step 3: Service API Integration

Step 4: Auth Implementation

Step 5: Zero Script QA

What is Zero Script QA?

RESTful API Principles

What is REST?

6 Core Principles

Uniform Interface Details

1. Resource-Based URLs

2. HTTP Method Meanings

3. HTTP Status Codes

4. Consistent Response Format

URL Design Rules

API Documentation Tools

API Design Checklist

Templates

Next Phase

Files

Compare with similar skills

Similar skills

More from ww-w-ai/bkit-claude-code

Related

Questions about Phase 4 API