jackspace/claudeskillz/claude-api

Name: claude-api
Author: jackspace

Trust tier 3

community

Source check pending

Checking that the SKILL.md file is still in the repository.

This skill provides comprehensive knowledge for working with the Anthropic Messages API (Claude API). It should be used when integrating Claude models into applications, implementing streaming responses, enabling prompt caching for cost savings, adding tool use (function calling), processing images with vision capabilities, or using extended thinking mode. Use when building chatbots, AI assistants, content generation tools, or any application requiring Claude's language understanding. Covers both server-side implementations (Node.js, Cloudflare Workers, Next.js) and direct API access. Keywords: claude api, anthropic api, messages api, @anthropic-ai/sdk, claude streaming, prompt caching, tool use, vision, extended thinking, claude 3.5 sonnet, claude 3.7 sonnet, claude sonnet 4, function calling, SSE, rate limits, 429 errors

Install

npx vskill@latest install jackspace/claudeskillz/claude-api

SKILL.md

Claude API (Anthropic Messages API)

Status: Production Ready Last Updated: 2025-10-25 Dependencies: None (standalone API skill) Latest Versions: @anthropic-ai/sdk@0.67.0

Quick Start (5 Minutes)

1. Get API Key

bash

# Sign up at https://console.anthropic.com/
# Navigate to API Keys section
# Create new key and save securely
export ANTHROPIC_API_KEY="sk-ant-..."

Why this matters:

API key required for all requests
Keep secure (never commit to git)
Use environment variables

2. Install SDK (Node.js)

bash

npm install @anthropic-ai/sdk

typescript

import Anthropic from '@anthropic-ai/sdk';
const anthropic = new Anthropic({
  apiKey: process.env.ANTHROPIC_API_KEY,
});
const message = await anthropic.messages.create({
  model: 'claude-sonnet-4-5-20250929',
  max_tokens: 1024,
  messages: [{ role: 'user', content: 'Hello, Claude!' }],
});
console.log(message.content[0].text);

CRITICAL:

Always use server-side (never expose API key in client code)
Set max_tokens (required parameter)
Model names are versioned (use latest stable)

3. Or Use Direct API (Cloudflare Workers)

typescript

// No SDK needed - use fetch()
const response = await fetch('https://api.anthropic.com/v1/messages', {
  method: 'POST',
  headers: {
    'x-api-key': env.ANTHROPIC_API_KEY,
    'anthropic-version': '2023-06-01',
    'content-type': 'application/json',
  },
  body: JSON.stringify({
    model: 'claude-sonnet-4-5-20250929',
    max_tokens: 1024,
    messages: [{ role: 'user', content: 'Hello!' }],
  }),
});
const data = await response.json();

Core API (Messages API)

Available Models (October 2025)

Model	ID	Context	Best For	Cost (per MTok)
Claude Sonnet 4.5	claude-sonnet-4-5-20250929	200k tokens	Balanced performance	$3/$15 (in/out)
Claude 3.7 Sonnet	claude-3-7-sonnet-20250228	2M tokens	Extended thinking	$3/$15
Claude Opus 4	claude-opus-4-20250514	200k tokens	Highest capability	$15/$75
Claude 3.5 Haiku	claude-3-5-haiku-20241022	200k tokens	Fast, cost-effective	$1/$5

Basic Message Creation

typescript

import Anthropic from '@anthropic-ai/sdk';
const anthropic = new Anthropic({
  apiKey: process.env.ANTHROPIC_API_KEY,
});
const message = await anthropic.messages.create({
  model: 'claude-sonnet-4-5-20250929',
  max_tokens: 1024,
  messages: [
    { role: 'user', content: 'Explain quantum computing in simple terms' }
  ],
});
console.log(message.content[0].text);

Multi-Turn Conversations

typescript

const messages = [
  { role: 'user', content: 'What is the capital of France?' },
  { role: 'assistant', content: 'The capital of France is Paris.' },
  { role: 'user', content: 'What is its population?' },
];
const message = await anthropic.messages.create({
  model: 'claude-sonnet-4-5-20250929',
  max_tokens: 1024,
  messages,
});

System Prompts

typescript

const message = await anthropic.messages.create({
  model: 'claude-sonnet-4-5-20250929',
  max_tokens: 1024,
  system: 'You are a helpful Python coding assistant. Always provide type hints and docstrings.',
  messages: [
    { role: 'user', content: 'Write a function to sort a list' }
  ],
});

CRITICAL:

System prompt MUST come before messages array
System prompt sets behavior for entire conversation
Can be 1-10k tokens (affects context window)

Streaming Responses (SSE)

Using SDK Stream Helper

typescript

const stream = anthropic.messages.stream({
  model: 'claude-sonnet-4-5-20250929',
  max_tokens: 1024,
  messages: [{ role: 'user', content: 'Write a short story' }],
});
// Method 1: Event listeners
stream
  .on('text', (text) => {
    process.stdout.write(text);
  })
  .on('message', (message) => {
    console.log('\n\nFinal message:', message);
  })
  .on('error', (error) => {
    console.error('Stream error:', error);
  });
// Wait for completion
await stream.finalMessage();

Streaming with Manual Iteration

typescript

const stream = await anthropic.messages.create({
  model: 'claude-sonnet-4-5-20250929',
  max_tokens: 1024,
  messages: [{ role: 'user', content: 'Explain AI' }],
  stream: true,
});
for await (const event of stream) {
  if (event.type === 'content_block_delta' && event.delta.type === 'text_delta') {
    process.stdout.write(event.delta.text);
  }
}

Streaming Event Types

Event	When	Use Case
`message_start`	Message begins	Initialize UI
`content_block_start`	New content block	Track blocks
`content_block_delta`	Text chunk received	Display text
`content_block_stop`	Block complete	Format block
`message_delta`	Metadata update	Update stop reason
`message_stop`	Message complete	Finalize UI

Cloudflare Workers Streaming

typescript

export default {
  async fetch(request: Request, env: Env): Promise<Response> {
    const response = await fetch('https://api.anthropic.com/v1/messages', {
      method: 'POST',
      headers: {
        'x-api-key': env.ANTHROPIC_API_KEY,
        'anthropic-version': '2023-06-01',
        'content-type': 'application/json',
      },
      body: JSON.stringify({
        model: 'claude-sonnet-4-5-20250929',
        max_tokens: 1024,
        messages: [{ role: 'user', content: 'Hello!' }],
        stream: true,
      }),
    });
    // Return SSE stream directly
    return new Response(response.body, {
      headers: {
        'Content-Type': 'text/event-stream',
        'Cache-Control': 'no-cache',
        'Connection': 'keep-alive',
      },
    });
  },
};

CRITICAL:

Errors can occur AFTER initial 200 response
Always implement error event handlers
Use stream.abort() to cancel
Set proper Content-Type headers

Prompt Caching (⭐ 90% Cost Savings)

Overview

Prompt caching allows you to cache frequently used context (system prompts, documents, codebases) to:

Reduce costs by 90% (cache reads = 10% of input token price)
Reduce latency by 85% (time to first token)
Cache lifetime: 5 minutes (default) or 1 hour (configurable)

Minimum Requirements

Claude 3.5 Sonnet: 1,024 tokens minimum
Claude 3.5 Haiku: 2,048 tokens minimum

Basic Prompt Caching

typescript

const message = await anthropic.messages.create({
  model: 'claude-sonnet-4-5-20250929',
  max_tokens: 1024,
  system: [
    {
      type: 'text',
      text: 'You are an AI assistant analyzing the following codebase...',
    },
    {
      type: 'text',
      text: LARGE_CODEBASE_CONTENT, // 50k tokens
      cache_control: { type: 'ephemeral' },
    },
  ],
  messages: [
    { role: 'user', content: 'Explain the auth module' }
  ],
});
// Check cache usage
console.log('Cache read tokens:', message.usage.cache_read_input_tokens);
console.log('Cache creation tokens:', message.usage.cache_creation_input_tokens);

Caching in Messages

typescript

const message = await anthropic.messages.create({
  model: 'claude-sonnet-4-5-20250929',
  max_tokens: 1024,
  messages: [
    {
      role: 'user',
      content: [
        {
          type: 'text',
          text: 'Analyze this documentation:',
        },
        {
          type: 'text',
          text: LONG_DOCUMENTATION, // 20k tokens
          cache_control: { type: 'ephemeral' },
        },
        {
          type: 'text',
          text: 'What are the main API endpoints?',
        },
      ],
    },
  ],
});

Multi-Turn Caching (Chatbot Pattern)

typescript

// First request - creates cache
const message1 = await anthropic.messages.create({
  model: 'claude-sonnet-4-5-20250929',
  max_tokens: 1024,
  system: [
    {
      type: 'text',
      text: SYSTEM_INSTRUCTIONS,
      cache_control: { type: 'ephemeral' },
    },
  ],
  messages: [
    { role: 'user', content: 'Hello!' }
  ],
});
// Second request - hits cache (within 5 minutes)
const message2 = await anthropic.messages.create({
  model: 'claude-sonnet-4-5-20250929',
  max_tokens: 1024,
  system: [
    {
      type: 'text',
      text: SYSTEM_INSTRUCTIONS, // Same content = cache hit
      cache_control: { type: 'ephemeral' },
    },
  ],
  messages: [
    { role: 'user', content: 'Hello!' },
    { role: 'assistant', content: message1.content[0].text },
    { role: 'user', content: 'Tell me a joke' },
  ],
});

Cost Comparison

Without Caching:
- 100k input tokens = 100k × $3/MTok = $0.30
 
With Caching (after first request):
- Cache write: 100k × $3.75/MTok = $0.375 (first request)
- Cache read: 100k × $0.30/MTok = $0.03 (subsequent requests)
- Savings: 90% per request after first

CRITICAL:

cache_control MUST be on LAST block of cacheable content
Cache shared across requests with IDENTICAL content
Monitor cache_creation_input_tokens vs cache_read_input_tokens
5-minute TTL refreshes on each use

Tool Use (Function Calling)

Basic Tool Definition

typescript

const tools = [
  {
    name: 'get_weather',
    description: 'Get the current weather in a given location',
    input_schema: {
      type: 'object',
      properties: {
        location: {
          type: 'string',
          description: 'City name, e.g. San Francisco, CA',
        },
        unit: {
          type: 'string',
          enum: ['celsius', 'fahrenheit'],
          description: 'Temperature unit',
        },
      },
      required: ['location'],
    },
  },
];
const message = await anthropic.messages.create({
  model: 'claude-sonnet-4-5-20250929',
  max_tokens: 1024,
  tools,
  messages: [{ role: 'user', content: 'What is the weather in NYC?' }],
});
if (message.stop_reason === 'tool_use') {
  const toolUse = message.content.find(block => block.type === 'tool_use');
  console.log('Claude wants to use:', toolUse.name);
  console.log('With parameters:', toolUse.input);
}

Tool Execution Loop

typescript

async function chatWithTools(userMessage: string) {
  const messages = [{ role: 'user', content: userMessage }];
  while (true) {
    const response = await anthropic.messages.create({
      model: 'claude-sonnet-4-5-20250929',
      max_tokens: 1024,
      tools,
      messages,
    });
    // Add assistant response
    messages.push({
      role: 'assistant',
      content: response.content,
    });
    // Check if tools need to be executed
    if (response.stop_reason === 'tool_use') {
      const toolResults = [];
      for (const block of response.content) {
        if (block.type === 'tool_use') {
          // Execute tool
          const result = await executeToolFunction(block.name, block.input);
          toolResults.push({
            type: 'tool_result',
            tool_use_id: block.id,
            content: JSON.stringify(result),
          });
        }
      }
      // Add tool results
      messages.push({
        role: 'user',
        content: toolResults,
      });
    } else {
      // Final response
      return response.content.find(block => block.type === 'text')?.text;
    }
  }
}

Beta Tool Runner (SDK Helper)

typescript

import { betaZodTool } from '@anthropic-ai/sdk/helpers/zod';
import { z } from 'zod';

This is the start of the file. Read the full SKILL.md on GitHub.

Security

Security scanPassed, 92 of 100Pattern checks on the skill's files.
Model reviewPassed

See the full security report

Quality evaluation

Task evaluationNot runNo evaluation yet. Run one in Skill Studio.

See evaluation results

Source

SKILL.md in the repositoryCheckingskills/claude-api/SKILL.md

Popularity

Repository stars: 12
Repository forks: 4
7-day trend score: 13

Stars and forks are for the whole GitHub repository, not this skill alone. Refreshed 2 Apr 2026, 6 months ago.

Works with

Any agent vskill installs to: 56 targets in all. These 39 have a page on this site.

Claude Code
Cursor
GitHub Copilot
Windsurf
Codex
Gemini CLI
Cline
Amp
Roo Code
Goose
Continue
Kilo Code
Junie
Trae
OpenHands
Qwen Code
AI Agent
Tabnine Chat
Sourcegraph Cody
Amazon Q
Firebase Genkit
Sweep
Devin
Phind
Mentat
Claude Desktop
Aider
GPT Pilot
Plandex
bolt.new
v0
Replit Agent
Anse
TypingMind
BetterChatGPT
LibreChat
Warp AI
Pieces
Fig AI

Embed badge

[![vskill VERIFIED](https://verified-skill.com/api/v1/skills/jackspace/claudeskillz/claude-api/badge)](https://verified-skill.com/skills/jackspace/claudeskillz/claude-api)

Something wrong with this skill or its page? Tell us.

Install

SKILL.md

Claude API (Anthropic Messages API)

Quick Start (5 Minutes)

1. Get API Key

2. Install SDK (Node.js)

3. Or Use Direct API (Cloudflare Workers)

The Complete Claude API Reference

Table of Contents

Core API (Messages API)

Available Models (October 2025)

Basic Message Creation

Multi-Turn Conversations

System Prompts

Streaming Responses (SSE)

Using SDK Stream Helper

Streaming with Manual Iteration

Streaming Event Types

Cloudflare Workers Streaming

Prompt Caching (⭐ 90% Cost Savings)

Overview

Minimum Requirements

Basic Prompt Caching

Caching in Messages

Multi-Turn Caching (Chatbot Pattern)

Cost Comparison

Tool Use (Function Calling)

Basic Tool Definition

Tool Execution Loop

Beta Tool Runner (SDK Helper)

Security

Quality evaluation

Source

Popularity

Works with