Api2cli

api2cli

Generate a working Node.js CLI from any API, then wrap it in a Claude Code skill. Discovers endpoints, scaffolds a dual-mode Commander.js CLI with a full-featured API client, and creates a skill folder so Claude knows how to use it.

Workflow

1. Identify the API -- user provides a docs URL, a live API base URL, or a peek-api capture
2. Discover endpoints -- parse docs, probe the API, or read a peek-api catalog
3. Build endpoint catalog -- normalize all discovered endpoints into a standard format
4. Generate CLI -- scaffold Commander.js CLI from the catalog
5. User chooses destination -- scaffold into current project or create standalone project
6. Generate skill -- create a SKILL.md that teaches Claude how to use the generated CLI

Step 1: Identify the API

Ask the user:

• "What API do you want to wrap? Share a docs URL, a base URL, or point me at a peek-api capture."

Determine which discovery paths to use based on what they provide:

Also ask:

• "What auth does this API use?" (API key, Bearer token, cookies, OAuth, none)
• "Do you want this CLI in your current project or as a standalone project?"

Step 2: Discover Endpoints

Use all applicable discovery paths. Combine results into a single catalog.

Path A: Docs Parsing

1. Fetch the docs URL with WebFetch
2. Extract endpoint information: method, path, description, parameters, request/response examples
3. Look for pagination patterns, auth requirements, rate limit info
4. Follow links to sub-pages for individual endpoint docs if the main page is an index

Path B: Active Probing

1. Check well-known paths for API specs:
   • /.well-known/openapi.json, /.well-known/openapi.yaml
   • /openapi.json, /openapi.yaml, /swagger.json, /swagger.yaml
   • /api-docs, /docs, /api/docs
   • /graphql (with introspection query)
2. Try OPTIONS on the base URL and common resource paths
3. Probe common REST patterns: /api/v1/, /api/v2/, /v1/, /v2/
4. For each discovered resource, try standard CRUD: GET /resources, GET /resources/:id, POST /resources, etc.
5. Parse response shapes to understand data models
6. Check response headers for rate limit info (X-RateLimit-*, Retry-After)
7. Check for pagination patterns in responses (next, cursor, page, offset)

See references/discovery-strategies.md for detailed probing patterns.

Path C: peek-api Capture

1. Read the capture directory: endpoints.json, auth.json, CAPTURE.md
2. Parse endpoints into the standard catalog format
3. Extract auth headers and cookies from auth.json

If peek-api is not installed or no capture exists, tell the user:

To capture endpoints from a live site, install peek-api:
  git clone https://github.com/alexknowshtml/peek-api
  cd peek-api && npm install
  node bin/cli.js https://example.com

Step 3: Build Endpoint Catalog

Normalize all discovered endpoints into this format:

interface EndpointCatalog {
  service: string;           // e.g., "stripe", "nexudus"
  baseUrl: string;
  auth: {
    type: 'api-key' | 'bearer' | 'cookies' | 'oauth' | 'none';
    headerName?: string;     // e.g., "Authorization", "X-API-Key"
    envVar: string;          // e.g., "STRIPE_API_KEY"
  };
  pagination?: {
    style: 'cursor' | 'offset' | 'page' | 'link-header';
    paramName: string;       // e.g., "starting_after", "offset", "page"
    responseField: string;   // e.g., "has_more", "next", "next_page_url"
  };
  rateLimit?: {
    requests: number;
    window: string;          // e.g., "1m", "1h"
  };
  resources: ResourceGroup[];
}

interface ResourceGroup {
  name: string;              // e.g., "customers", "invoices"
  description: string;
  endpoints: Endpoint[];
}

interface Endpoint {
  method: 'GET' | 'POST' | 'PUT' | 'PATCH' | 'DELETE';
  path: string;              // e.g., "/v1/customers/:id"
  description: string;
  parameters: Parameter[];
  requestBody?: object;      // JSON schema or example
  responseExample?: object;
}

interface Parameter {
  name: string;
  in: 'path' | 'query' | 'header';
  required: boolean;
  type: string;
  description: string;
}

Present the catalog to the user for review before generating:

Found 24 endpoints across 5 resources:
  customers (6 endpoints): list, get, create, update, delete, search
  invoices (5 endpoints): list, get, create, send, void
  ...
Ready to generate the CLI?

Step 4: Generate CLI

Generate a dual-mode CLI using Commander.js. The CLI auto-detects human vs agent output via process.stdout.isTTY.

File Structure

In-project scaffold:

scripts/
  {service}.ts                    # Entry point with shebang
  {service}/
    lib/
      client.ts                   # API client (auth, pagination, retry, caching)
      envelope.ts                 # Agent JSON envelope helpers
    commands/
      {resource}.ts               # One file per resource group

Standalone project:

{service}-cli/
  package.json
  tsconfig.json
  bin/
    {service}.ts                  # Entry point with shebang
  src/
    lib/
      client.ts
      envelope.ts
    commands/
      {resource}.ts

Code Generation Patterns

See these references for the patterns to apply during generation:

• references/api-client-template.md -- API client class with pagination, retry, rate limiting, caching
• references/agent-first-patterns.md -- JSON envelope, HATEOAS next_actions, context-safe output, error fix suggestions
• references/commander-patterns.md -- Commander.js subcommands, global options, interactive prompts, colored output

Key Generation Rules

Entry point ({service}.ts):

• Shebang: #!/usr/bin/env npx tsx
• Self-documenting root command (no args → prints full command tree as JSON)
• Global options: --json (force JSON output), --verbose, --config <path>

API client (lib/client.ts):

• Constructor takes base URL + auth config
• Auth from env var (name based on catalog.auth.envVar)
• Built-in pagination matching the API's pattern
• Retry with exponential backoff for 5xx and 429 errors
• Rate limiting based on discovered limits
• Optional response caching

Envelope helpers (lib/envelope.ts):

const isAgent = !process.stdout.isTTY;

function respond(command: string, result: any, nextActions: Action[] = []) {
  if (isAgent) {
    console.log(JSON.stringify({ ok: true, command, result, next_actions: nextActions }));
  } else {
    return result; // caller handles human rendering
  }
}

function respondError(command: string, message: string, code: string, fix: string, nextActions: Action[] = []) {
  if (isAgent) {
    console.log(JSON.stringify({ ok: false, command, error: { message, code }, fix, next_actions: nextActions }));
  } else {
    console.error(`Error: ${message}`);
    console.error(`Fix: ${fix}`);
  }
  process.exit(1);
}

Command files (commands/{resource}.ts):

• One file per resource group
• Each endpoint becomes a subcommand: mycli customers list, mycli customers get <id>
• list commands: support --limit, --offset/--cursor, --status (if filterable)
• get commands: take ID as argument
• create/update commands: accept --data <json> or individual --field flags
• Every command includes contextual next_actions for agent mode
• Errors include fix suggestions

Standalone project extras:

• package.json with commander, tsx as dependencies, bin field pointing to entry
• tsconfig.json for TypeScript
• .env.example with the required env var

Step 5: Verify

After generating the CLI:

1. Verify it runs: Execute with no args, confirm the self-documenting root works
2. Test one endpoint: Pick a simple GET endpoint, run it, verify output
3. Move on to Step 6 to wrap the CLI in a skill

Step 6: Generate Skill

Create a Claude Code skill folder that teaches Claude how to use the generated CLI. This is the final step -- it turns the CLI into something any Claude session can pick up and use without reading the code.

Skill Structure

.claude/skills/{service}/
  SKILL.md                    # Skill instructions

SKILL.md Template

Generate a SKILL.md with this structure:

---
name: {service}
description: Interact with the {Service} API via CLI. Use when user wants to
  {list of actions based on discovered resources, e.g., "list customers,
  create invoices, check order status"}. Commands: {service} {resource} {action}.
---

# {Service} CLI

CLI wrapper for the {Service} API.

## Setup

Set the `{SERVICE_ENV_VAR}` environment variable:
\`\`\`bash
export {SERVICE_ENV_VAR}=your-api-key-here
\`\`\`

## Commands

{For each resource group, list commands with examples:}

### {Resource}

\`\`\`bash
# List {resources}
npx tsx {path/to/cli}.ts {resource} list

# Get a specific {resource}
npx tsx {path/to/cli}.ts {resource} get <id>

# Create a {resource}
npx tsx {path/to/cli}.ts {resource} create --field value
\`\`\`

## Common Workflows

{Generate 2-3 practical workflows combining multiple commands:}

### Example: {Workflow name}
\`\`\`bash
# Step 1: Find the customer
npx tsx {path/to/cli}.ts customers list --status=active

# Step 2: Get their invoices
npx tsx {path/to/cli}.ts invoices list --customer-id=abc123
\`\`\`

## Agent Usage

When piped, all commands return JSON with `next_actions`:
\`\`\`bash
npx tsx {path/to/cli}.ts {resource} list | cat
\`\`\`

Key Rules for Skill Generation

1. Description is critical -- include specific trigger phrases and list the actions the CLI supports. This is what Claude reads to decide when to use the skill.
2. Include real command examples -- use the actual CLI path and real subcommand names from the generated CLI.
3. Generate practical workflows -- combine multiple commands into realistic multi-step scenarios based on how the API's resources relate to each other.
4. Keep it lean -- the skill should be a quick reference, not a restatement of --help. Focus on what Claude needs to know that it can't infer.

Tell the User

After generating both the CLI and the skill:

CLI generated at {cli_path}
Skill generated at .claude/skills/{service}/SKILL.md

To use the CLI directly:
  npx tsx {cli_path}                           # See all commands
  npx tsx {cli_path} customers list            # List customers

Claude will now automatically use this skill when you ask about {service}.

Reference Files

• references/discovery-strategies.md -- Detailed probing patterns, well-known paths, GraphQL introspection, response parsing
• references/api-client-template.md -- Full API client class with pagination, retry, rate limiting, caching
• references/agent-first-patterns.md -- Agent JSON envelope, HATEOAS, context-safe output, error handling
• references/commander-patterns.md -- Commander.js subcommands, nested commands, interactive prompts, colored output, config files, testing