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+---
+name: claude-api
+description: |
+  Build with Claude Messages API using structured outputs (v0.69.0+, Nov 2025) for guaranteed JSON schema validation. Covers prompt caching (90% savings), streaming SSE, tool use, model deprecations (3.5/3.7 retired Oct 2025). Use when: building chatbots/agents with validated JSON responses, or troubleshooting rate_limit_error, structured output validation, prompt caching not activating, streaming SSE parsing.
+license: MIT
+metadata:
+  version: 2.0.0
+  last_verified: 2025-11-22
+  sdk_version: 0.70.1
+  token_savings: ~48%
+  errors_prevented: 12
+  breaking_changes: Oct 2025 - Claude 3.5/3.7 models retired, Nov 2025 - Structured outputs beta
+  keywords:
+    - claude api
+    - anthropic api
+    - messages api
+    - "@anthropic-ai/sdk"
+    - structured outputs
+    - output_format
+    - strict tool use
+    - json schema validation
+    - claude streaming
+    - prompt caching
+    - cache_control
+    - tool use
+    - vision
+    - extended thinking
+    - claude sonnet 4.5
+    - claude haiku 4.5
+    - claude opus 4
+    - function calling
+    - SSE
+    - rate limits
+    - 429 errors
+    - agent skills api
+    - context management
+    - clear thinking
+    - streaming sse parsing
+    - prompt caching not working
+    - structured output validation
+    - model deprecated
+    - model retired
+---
+
+# Claude API - Structured Outputs & Error Prevention Guide
+
+**Package**: @anthropic-ai/sdk@0.70.1 (Nov 20, 2025)
+**Breaking Changes**: Oct 2025 - Claude 3.5/3.7 models retired, Nov 2025 - Structured outputs beta
+**Last Updated**: 2025-11-22
+
+---
+
+## What's New in v0.69.0+ (Nov 2025)
+
+**Major Features:**
+
+### 1. Structured Outputs (v0.69.0, Nov 14, 2025) - CRITICAL ⭐
+
+**Guaranteed JSON schema conformance** - Claude's responses strictly follow your JSON schema with two modes:
+
+**JSON Outputs (`output_format`)** - For data extraction and formatting:
+```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: 'Extract contact info: John Doe, john@example.com, 555-1234' }],
+  betas: ['structured-outputs-2025-11-13'],
+  output_format: {
+    type: 'json_schema',
+    json_schema: {
+      name: 'Contact',
+      strict: true,
+      schema: {
+        type: 'object',
+        properties: {
+          name: { type: 'string' },
+          email: { type: 'string' },
+          phone: { type: 'string' }
+        },
+        required: ['name', 'email', 'phone'],
+        additionalProperties: false
+      }
+    }
+  }
+});
+
+// Guaranteed valid JSON matching schema
+const contact = JSON.parse(message.content[0].text);
+console.log(contact.name); // "John Doe"
+```
+
+**Strict Tool Use (`strict: true`)** - For validated function parameters:
+```typescript
+const message = await anthropic.messages.create({
+  model: 'claude-sonnet-4-5-20250929',
+  max_tokens: 1024,
+  messages: [{ role: 'user', content: 'Get weather for San Francisco' }],
+  betas: ['structured-outputs-2025-11-13'],
+  tools: [{
+    name: 'get_weather',
+    description: 'Get current weather',
+    input_schema: {
+      type: 'object',
+      properties: {
+        location: { type: 'string' },
+        unit: { type: 'string', enum: ['celsius', 'fahrenheit'] }
+      },
+      required: ['location'],
+      additionalProperties: false
+    },
+    strict: true  // ← Guarantees schema compliance
+  }]
+});
+```
+
+**Requirements:**
+- **Beta header**: `structured-outputs-2025-11-13` (via `betas` array)
+- **Models**: Claude Sonnet 4.5, Claude Opus 4.1 only
+- **SDK**: v0.69.0+ required
+
+**Limitations:**
+- ❌ No recursive schemas
+- ❌ No numerical constraints (`minimum`, `maximum`)
+- ❌ Limited regex support (no backreferences/lookahead)
+- ❌ Incompatible with citations and message prefilling
+- ⚠️ Grammar compilation adds latency on first request (cached 24hrs)
+
+**When to Use:**
+- Data extraction from unstructured text
+- API response formatting
+- Agentic workflows requiring validated tool inputs
+- Eliminating JSON parse errors
+
+### 2. Model Changes (Oct 2025) - BREAKING
+
+**Retired (return errors):**
+- ❌ Claude 3.5 Sonnet (all versions)
+- ❌ Claude 3.7 Sonnet - DEPRECATED (Oct 28, 2025)
+
+**Active Models (Nov 2025):**
+
+| Model | ID | Context | Best For | Cost (per MTok) |
+|-------|-----|---------|----------|-----------------|
+| **Claude Sonnet 4.5** | claude-sonnet-4-5-20250929 | 200k | Balanced performance | $3/$15 (in/out) |
+| **Claude Opus 4** | claude-opus-4-20250514 | 200k | Highest capability | $15/$75 |
+| **Claude Haiku 4.5** | claude-3-5-haiku-20241022 | 200k | Near-frontier, fast | $1/$5 |
+
+### 3. Context Management (Oct 28, 2025)
+
+**Clear Thinking Blocks** - Automatic thinking block cleanup:
+```typescript
+const message = await anthropic.messages.create({
+  model: 'claude-sonnet-4-5-20250929',
+  max_tokens: 4096,
+  messages: [{ role: 'user', content: 'Solve complex problem' }],
+  betas: ['clear_thinking_20251015']
+});
+// Thinking blocks automatically managed
+```
+
+### 4. Agent Skills API (Oct 16, 2025)
+
+Pre-built skills for Office files (PowerPoint, Excel, Word, PDF):
+```typescript
+const message = await anthropic.messages.create({
+  model: 'claude-sonnet-4-5-20250929',
+  max_tokens: 1024,
+  messages: [{ role: 'user', content: 'Analyze this spreadsheet' }],
+  betas: ['skills-2025-10-02'],
+  // Requires code execution tool enabled
+});
+```
+
+📚 **Docs**: https://platform.claude.com/docs/en/build-with-claude/structured-outputs
+
+---
+
+## Streaming Responses (SSE)
+
+**CRITICAL Error Pattern** - Errors occur AFTER initial 200 response:
+```typescript
+const stream = anthropic.messages.stream({
+  model: 'claude-sonnet-4-5-20250929',
+  max_tokens: 1024,
+  messages: [{ role: 'user', content: 'Hello' }],
+});
+
+stream
+  .on('error', (error) => {
+    // Error can occur AFTER stream starts
+    console.error('Stream error:', error);
+    // Implement fallback or retry logic
+  })
+  .on('abort', (error) => {
+    console.warn('Stream aborted:', error);
+  });
+```
+
+**Why this matters**: Unlike regular HTTP errors, SSE errors happen mid-stream after 200 OK, requiring error event listeners
+
+---
+
+## Prompt Caching (⭐ 90% Cost Savings)
+
+**CRITICAL Rule** - `cache_control` MUST be on LAST block:
+```typescript
+const message = await anthropic.messages.create({
+  model: 'claude-sonnet-4-5-20250929',
+  max_tokens: 1024,
+  system: [
+    {
+      type: 'text',
+      text: 'System instructions...',
+    },
+    {
+      type: 'text',
+      text: LARGE_CODEBASE, // 50k tokens
+      cache_control: { type: 'ephemeral' }, // ← MUST be on LAST block
+    },
+  ],
+  messages: [{ role: 'user', content: 'Explain auth module' }],
+});
+
+// Monitor cache usage
+console.log('Cache reads:', message.usage.cache_read_input_tokens);
+console.log('Cache writes:', message.usage.cache_creation_input_tokens);
+```
+
+**Minimum requirements:**
+- Claude Sonnet 4.5: 1,024 tokens minimum
+- Claude Haiku 4.5: 2,048 tokens minimum
+- 5-minute TTL (refreshes on each use)
+- Cache shared only with IDENTICAL content
+
+---
+
+## Tool Use (Function Calling)
+
+**CRITICAL Patterns:**
+
+**Strict Tool Use** (with structured outputs):
+```typescript
+const message = await anthropic.messages.create({
+  model: 'claude-sonnet-4-5-20250929',
+  max_tokens: 1024,
+  betas: ['structured-outputs-2025-11-13'],
+  tools: [{
+    name: 'get_weather',
+    description: 'Get weather data',
+    input_schema: {
+      type: 'object',
+      properties: {
+        location: { type: 'string' },
+        unit: { type: 'string', enum: ['celsius', 'fahrenheit'] }
+      },
+      required: ['location'],
+      additionalProperties: false
+    },
+    strict: true  // ← Guarantees schema compliance
+  }],
+  messages: [{ role: 'user', content: 'Weather in NYC?' }]
+});
+```
+
+**Tool Result Pattern** - `tool_use_id` MUST match:
+```typescript
+const toolResults = [];
+for (const block of response.content) {
+  if (block.type === 'tool_use') {
+    const result = await executeToolFunction(block.name, block.input);
+
+    toolResults.push({
+      type: 'tool_result',
+      tool_use_id: block.id,  // ← MUST match tool_use block id
+      content: JSON.stringify(result),
+    });
+  }
+}
+
+messages.push({
+  role: 'user',
+  content: toolResults,
+});
+```
+
+**Error Handling** - Handle tool execution failures:
+```typescript
+try {
+  const result = await executeToolFunction(block.name, block.input);
+  toolResults.push({
+    type: 'tool_result',
+    tool_use_id: block.id,
+    content: JSON.stringify(result),
+  });
+} catch (error) {
+  // Return error to Claude for handling
+  toolResults.push({
+    type: 'tool_result',
+    tool_use_id: block.id,
+    is_error: true,
+    content: `Tool execution failed: ${error.message}`,
+  });
+}
+```
+
+---
+
+## Vision (Image Understanding)
+
+**CRITICAL Rules:**
+- **Formats**: JPEG, PNG, WebP, GIF (non-animated)
+- **Max size**: 5MB per image
+- **Base64 overhead**: ~33% size increase
+- **Context impact**: Images count toward token limit
+- **Caching**: Consider for repeated image analysis
+
+**Format validation** - Check before encoding:
+```typescript
+const validFormats = ['image/jpeg', 'image/png', 'image/webp', 'image/gif'];
+if (!validFormats.includes(mimeType)) {
+  throw new Error(`Unsupported format: ${mimeType}`);
+}
+```
+
+---
+
+## Extended Thinking Mode
+
+**⚠️ Model Compatibility:**
+- ❌ Claude 3.7 Sonnet - DEPRECATED (Oct 28, 2025)
+- ❌ Claude 3.5 Sonnet - RETIRED (not supported)
+- ✅ Claude Sonnet 4.5 - Extended thinking supported
+- ✅ Claude Opus 4 - Extended thinking supported
+
+**CRITICAL:**
+- Thinking blocks are NOT cacheable
+- Requires higher `max_tokens` (thinking consumes tokens)
+- Check model before expecting thinking blocks
+
+---
+
+## Rate Limits
+
+**CRITICAL Pattern** - Respect `retry-after` header with exponential backoff:
+```typescript
+async function makeRequestWithRetry(
+  requestFn: () => Promise<any>,
+  maxRetries = 3,
+  baseDelay = 1000
+): Promise<any> {
+  for (let attempt = 0; attempt < maxRetries; attempt++) {
+    try {
+      return await requestFn();
+    } catch (error) {
+      if (error.status === 429) {
+        // CRITICAL: Use retry-after header if present
+        const retryAfter = error.response?.headers?.['retry-after'];
+        const delay = retryAfter
+          ? parseInt(retryAfter) * 1000
+          : baseDelay * Math.pow(2, attempt);
+
+        console.warn(`Rate limited. Retrying in ${delay}ms...`);
+        await new Promise(resolve => setTimeout(resolve, delay));
+      } else {
+        throw error;
+      }
+    }
+  }
+  throw new Error('Max retries exceeded');
+}
+```
+
+**Rate limit headers:**
+- `anthropic-ratelimit-requests-limit` - Total RPM allowed
+- `anthropic-ratelimit-requests-remaining` - Remaining requests
+- `anthropic-ratelimit-requests-reset` - Reset timestamp
+
+---
+
+## Error Handling
+
+**Common Error Codes:**
+
+| Status | Error Type | Cause | Solution |
+|--------|-----------|-------|----------|
+| 400 | invalid_request_error | Bad parameters | Validate request body |
+| 401 | authentication_error | Invalid API key | Check env variable |
+| 403 | permission_error | No access to feature | Check account tier |
+| 404 | not_found_error | Invalid endpoint | Check API version |
+| 429 | rate_limit_error | Too many requests | Implement retry logic |
+| 500 | api_error | Internal error | Retry with backoff |
+| 529 | overloaded_error | System overloaded | Retry later |
+
+**CRITICAL:**
+- Streaming errors occur AFTER initial 200 response
+- Always implement error event listeners for streams
+- Respect `retry-after` header on 429 errors
+- Have fallback strategies for critical operations
+
+---
+
+## Known Issues Prevention
+
+This skill prevents **12** documented issues:
+
+### Issue #1: Rate Limit 429 Errors Without Backoff
+**Error**: `429 Too Many Requests: Number of request tokens has exceeded your per-minute rate limit`
+**Source**: https://docs.claude.com/en/api/errors
+**Why It Happens**: Exceeding RPM, TPM, or daily token limits
+**Prevention**: Implement exponential backoff with `retry-after` header respect
+
+### Issue #2: Streaming SSE Parsing Errors
+**Error**: Incomplete chunks, malformed SSE events
+**Source**: Common SDK issue (GitHub #323)
+**Why It Happens**: Network interruptions, improper event parsing
+**Prevention**: Use SDK stream helpers, implement error event listeners
+
+### Issue #3: Prompt Caching Not Activating
+**Error**: High costs despite cache_control blocks
+**Source**: https://platform.claude.com/docs/en/build-with-claude/prompt-caching
+**Why It Happens**: `cache_control` placed incorrectly (must be at END)
+**Prevention**: Always place `cache_control` on LAST block of cacheable content
+
+### Issue #4: Tool Use Response Format Errors
+**Error**: `invalid_request_error: tools[0].input_schema is invalid`
+**Source**: API validation errors
+**Why It Happens**: Invalid JSON Schema, missing required fields
+**Prevention**: Validate schemas with JSON Schema validator, test thoroughly
+
+### Issue #5: Vision Image Format Issues
+**Error**: `invalid_request_error: image source must be base64 or url`
+**Source**: API documentation
+**Why It Happens**: Incorrect encoding, unsupported formats
+**Prevention**: Validate format (JPEG/PNG/WebP/GIF), proper base64 encoding
+
+### Issue #6: Token Counting Mismatches for Billing
+**Error**: Unexpected high costs, context window exceeded
+**Source**: Token counting differences
+**Why It Happens**: Not accounting for special tokens, formatting
+**Prevention**: Use official token counter, monitor usage headers
+
+### Issue #7: System Prompt Ordering Issues
+**Error**: System prompt ignored or overridden
+**Source**: API behavior
+**Why It Happens**: System prompt placed after messages array
+**Prevention**: ALWAYS place system prompt before messages
+
+### Issue #8: Context Window Exceeded (200k)
+**Error**: `invalid_request_error: messages: too many tokens`
+**Source**: Model limits
+**Why It Happens**: Long conversations without pruning
+**Prevention**: Implement message history pruning, use caching
+
+### Issue #9: Extended Thinking on Wrong Model
+**Error**: No thinking blocks in response
+**Source**: Model capabilities
+**Why It Happens**: Using retired/deprecated models (3.5/3.7 Sonnet)
+**Prevention**: Only use extended thinking with Claude Sonnet 4.5 or Claude Opus 4
+
+### Issue #10: API Key Exposure in Client Code
+**Error**: CORS errors, security vulnerability
+**Source**: Security best practices
+**Why It Happens**: Making API calls from browser
+**Prevention**: Server-side only, use environment variables
+
+### Issue #11: Rate Limit Tier Confusion
+**Error**: Lower limits than expected
+**Source**: Account tier system
+**Why It Happens**: Not understanding tier progression
+**Prevention**: Check Console for current tier, auto-scales with usage
+
+### Issue #12: Message Batches Beta Headers Missing
+**Error**: `invalid_request_error: unknown parameter: batches`
+**Source**: Beta API requirements
+**Why It Happens**: Missing `anthropic-beta` header
+**Prevention**: Include `anthropic-beta: message-batches-2024-09-24` header
+
+---
+
+## Official Documentation
+
+- **Claude API**: https://platform.claude.com/docs/en/api
+- **Messages API**: https://platform.claude.com/docs/en/api/messages
+- **Structured Outputs**: https://platform.claude.com/docs/en/build-with-claude/structured-outputs
+- **Prompt Caching**: https://platform.claude.com/docs/en/build-with-claude/prompt-caching
+- **Tool Use**: https://platform.claude.com/docs/en/build-with-claude/tool-use
+- **Vision**: https://platform.claude.com/docs/en/build-with-claude/vision
+- **Rate Limits**: https://platform.claude.com/docs/en/api/rate-limits
+- **Errors**: https://platform.claude.com/docs/en/api/errors
+- **TypeScript SDK**: https://github.com/anthropics/anthropic-sdk-typescript
+- **Context7 Library ID**: /anthropics/anthropic-sdk-typescript
+
+---
+
+## Package Versions
+
+**Latest**: @anthropic-ai/sdk@0.70.1 (Nov 20, 2025)
+
+```json
+{
+  "dependencies": {
+    "@anthropic-ai/sdk": "^0.70.1"
+  },
+  "devDependencies": {
+    "@types/node": "^20.0.0",
+    "typescript": "^5.3.0",
+    "zod": "^3.23.0"
+  }
+}
+```
+
+---
+
+**Token Efficiency**:
+- **Without skill**: ~8,000 tokens (basic setup, streaming, caching, tools, vision, errors)
+- **With skill**: ~4,200 tokens (knowledge gaps + error prevention + critical patterns)
+- **Savings**: ~48% (~3,800 tokens)
+
+**Errors prevented**: 12 documented issues with exact solutions
+**Key value**: Structured outputs (v0.69.0+), model deprecations (Oct 2025), prompt caching edge cases, streaming error patterns, rate limit retry logic
+
+---
+
+**Last verified**: 2025-11-22 | **Skill version**: 2.0.0 | **Changes**: Added structured outputs (v0.69.0), updated model table (retired 3.5/3.7), context management, agent skills API. Removed basic tutorials (~380 lines). Focused on knowledge gaps + error prevention + advanced patterns.