Claude Agent SDK - Structured Outputs & Error Prevention Guide

Package: @anthropic-ai/claude-agent-sdk@0.2.12 Breaking Changes: v0.1.45 - Structured outputs (Nov 2025), v0.1.0 - No default system prompt, settingSources required

What's New in v0.1.45+ (Nov 2025)

Major Features:

1. Structured Outputs (v0.1.45, Nov 14, 2025)

JSON schema validation - Guarantees responses match exact schemas
outputFormat parameter - Define output structure with JSON schema or Zod
Access validated results - Via message.structured_output
Beta header required: structured-outputs-2025-11-13
Type safety - Full TypeScript inference with Zod schemas

Example:

import { query } from "@anthropic-ai/claude-agent-sdk";
import { z } from "zod";
import { zodToJsonSchema } from "zod-to-json-schema";

const schema = z.object({
  summary: z.string(),
  sentiment: z.enum(['positive', 'neutral', 'negative']),
  confidence: z.number().min(0).max(1)
});

const response = query({
  prompt: "Analyze this code review feedback",
  options: {
    model: "claude-sonnet-4-5",
    outputFormat: {
      type: "json_schema",
      json_schema: {
        name: "AnalysisResult",
        strict: true,
        schema: zodToJsonSchema(schema)
      }
    }
  }
});

for await (const message of response) {
  if (message.type === 'result' && message.structured_output) {
    // Guaranteed to match schema
    const validated = schema.parse(message.structured_output);
    console.log(`Sentiment: ${validated.sentiment}`);
  }
}

Zod Compatibility (v0.1.71+): SDK supports both Zod v3.24.1+ and Zod v4.0.0+ as peer dependencies. Import remains import { z } from "zod" for either version.

2. Plugins System (v0.1.27)

plugins array - Load local plugin paths
Custom plugin support - Extend agent capabilities

3. Hooks System (v0.1.0+)

All 12 Hook Events:

Hook	When Fired	Use Case
`PreToolUse`	Before tool execution	Validate, modify, or block tool calls
`PostToolUse`	After tool execution	Log results, trigger side effects
`Notification`	Agent notifications	Display status updates
`UserPromptSubmit`	User prompt received	Pre-process or validate input
`SubagentStart`	Subagent spawned	Track delegation, log context
`SubagentStop`	Subagent completed	Aggregate results, cleanup
`PreCompact`	Before context compaction	Save state before truncation
`PermissionRequest`	Permission needed	Custom approval workflows
`Stop`	Agent stopping	Cleanup, final logging
`SessionStart`	Session begins	Initialize state
`SessionEnd`	Session ends	Persist state, cleanup
`Error`	Error occurred	Custom error handling

Hook Configuration:

const response = query({
  prompt: "...",
  options: {
    hooks: {
      PreToolUse: async (input) => {
        console.log(`Tool: ${input.toolName}`);
        return { allow: true };  // or { allow: false, message: "..." }
      },
      PostToolUse: async (input) => {
        await logToolUsage(input.toolName, input.result);
      }
    }
  }
});

4. Additional Options

fallbackModel - Automatic model fallback on failures
maxThinkingTokens - Control extended thinking budget
strictMcpConfig - Strict MCP configuration validation
continue - Resume with new prompt (differs from resume)
permissionMode: 'plan' - New permission mode for planning workflows

📚 Docs: https://platform.claude.com/docs/en/agent-sdk/structured-outputs

Core Query API

Key signature:

query(prompt: string | AsyncIterable<SDKUserMessage>, options?: Options)
  -> AsyncGenerator<SDKMessage>

Critical Options:

outputFormat - Structured JSON schema validation (v0.1.45+)
settingSources - Filesystem settings loading ('user'|'project'|'local')
canUseTool - Custom permission logic callback
agents - Programmatic subagent definitions
mcpServers - MCP server configuration
permissionMode - 'default'|'acceptEdits'|'bypassPermissions'|'plan'
betas - Enable beta features (e.g., 1M context window)
sandbox - Sandbox settings for secure execution
enableFileCheckpointing - Enable file state snapshots
systemPrompt - System prompt (string or preset object)

Extended Context (1M Tokens)

Enable 1 million token context window:

const response = query({
  prompt: "Analyze this large codebase",
  options: {
    betas: ['context-1m-2025-08-07'],  // Enable 1M context
    model: "claude-sonnet-4-5"
  }
});

System Prompt Configuration

Two forms of systemPrompt:

// 1. Simple string
systemPrompt: "You are a helpful coding assistant."

// 2. Preset with optional append (preserves Claude Code defaults)
systemPrompt: {
  type: 'preset',
  preset: 'claude_code',
  append: "\n\nAdditional context: Focus on security."
}

Use preset form when you want Claude Code's default behaviors plus custom additions.

Tool Integration (Built-in + Custom)

Tool Control:

allowedTools - Whitelist (takes precedence)
disallowedTools - Blacklist
canUseTool - Custom permission callback (see Permission Control section)

Built-in Tools: Read, Write, Edit, Bash, Grep, Glob, WebSearch, WebFetch, Task, NotebookEdit, BashOutput, KillBash, ListMcpResources, ReadMcpResource, AskUserQuestion

AskUserQuestion Tool (v0.1.71+)

Enable user interaction during agent execution:

const response = query({
  prompt: "Review and refactor the codebase",
  options: {
    allowedTools: ["Read", "Write", "Edit", "AskUserQuestion"]
  }
});

// Agent can now ask clarifying questions
// Questions appear in message stream as tool_call with name "AskUserQuestion"

Use cases:

Clarify ambiguous requirements mid-task
Get user approval before destructive operations
Present options and get selection

Tools Configuration (v0.1.57+)

Three forms of tool configuration:

// 1. Exact allowlist (string array)
tools: ["Read", "Write", "Grep"]

// 2. Disable all tools (empty array)
tools: []

// 3. Preset with defaults (object form)
tools: { type: 'preset', preset: 'claude_code' }

Note: allowedTools and disallowedTools still work but tools provides more flexibility.

MCP Servers (Model Context Protocol)

Server Types:

In-process - createSdkMcpServer() with tool() definitions
External - stdio, HTTP, SSE transport

Tool Definition:

tool(name: string, description: string, zodSchema, handler)

Handler Return:

{ content: [{ type: "text", text: "..." }], isError?: boolean }

External MCP Servers (stdio)

const response = query({
  prompt: "List files and analyze Git history",
  options: {
    mcpServers: {
      // Filesystem server
      "filesystem": {
        command: "npx",
        args: ["@modelcontextprotocol/server-filesystem"],
        env: {
          ALLOWED_PATHS: "/Users/developer/projects:/tmp"
        }
      },
      // Git operations server
      "git": {
        command: "npx",
        args: ["@modelcontextprotocol/server-git"],
        env: {
          GIT_REPO_PATH: "/Users/developer/projects/my-repo"
        }
      }
    },
    allowedTools: [
      "mcp__filesystem__list_files",
      "mcp__filesystem__read_file",
      "mcp__git__log",
      "mcp__git__diff"
    ]
  }
});

External MCP Servers (HTTP/SSE)

const response = query({
  prompt: "Analyze data from remote service",
  options: {
    mcpServers: {
      "remote-service": {
        url: "https://api.example.com/mcp",
        headers: {
          "Authorization": "Bearer your-token-here",
          "Content-Type": "application/json"
        }
      }
    },
    allowedTools: ["mcp__remote-service__analyze"]
  }
});

MCP Tool Naming Convention

Format: mcp__<server-name>__<tool-name>

CRITICAL:

Server name and tool name MUST match configuration
Use double underscores (__) as separators
Include in allowedTools array

Examples: mcp__weather-service__get_weather, mcp__filesystem__read_file

Subagent Orchestration

AgentDefinition Type

type AgentDefinition = {
  description: string;        // When to use this agent
  prompt: string;             // System prompt for agent
  tools?: string[];           // Allowed tools (optional)
  model?: 'sonnet' | 'opus' | 'haiku' | 'inherit';  // Model (optional)
  skills?: string[];          // Skills to load (v0.2.10+)
  maxTurns?: number;          // Maximum turns before stopping (v0.2.10+)
}

Field Details:

description: When to use agent (used by main agent for delegation)
prompt: System prompt (defines role, inherits main context)
tools: Allowed tools (if omitted, inherits from main agent)
model: Model override (haiku/sonnet/opus/inherit)
skills: Skills to load for agent (v0.2.10+)
maxTurns: Limit agent to N turns before returning control (v0.2.10+)

Usage:

agents: {
  "security-checker": {
    description: "Security audits and vulnerability scanning",
    prompt: "You check security. Scan for secrets, verify OWASP compliance.",
    tools: ["Read", "Grep", "Bash"],
    model: "sonnet",
    skills: ["security-best-practices"],  // Load specific skills
    maxTurns: 10  // Limit to 10 turns
  }
}

⚠️ Subagent Cleanup Warning

Known Issue: Subagents don't stop when parent agent stops (Issue #132)

When a parent agent is stopped (via cancellation or error), spawned subagents continue running as orphaned processes. This can lead to:

Resource leaks
Continued tool execution after parent stopped
RAM out-of-memory in recursive scenarios (Claude Code Issue #4850)

Workaround: Implement cleanup in Stop hooks:

const response = query({
  prompt: "Deploy to production",
  options: {
    agents: {
      "deployer": {
        description: "Handle deployments",
        prompt: "Deploy the application",
        tools: ["Bash"]
      }
    },
    hooks: {
      Stop: async (input) => {
        // Manual cleanup of spawned processes
        console.log("Parent stopped - cleaning up subagents");
        // Implement process tracking and termination
      }
    }
  }
});

Enhancement Tracking: Issue #142 proposes auto-termination

Session Management

Options:

resume: sessionId - Continue previous session
forkSession: true - Create new branch from session
continue: prompt - Resume with new prompt (differs from resume)

Session Forking Pattern (Unique Capability):

// Explore alternative without modifying original
const forked = query({
  prompt: "Try GraphQL instead of REST",
  options: {
    resume: sessionId,
    forkSession: true  // Creates new branch, original session unchanged
  }
});

Capture Session ID:

for await (const message of response) {
  if (message.type === 'system' && message.subtype === 'init') {
    sessionId = message.session_id;  // Save for later resume/fork
  }
}

V2 Session APIs (Preview - v0.1.54+)

Simpler multi-turn conversation pattern:

import {
  unstable_v2_createSession,
  unstable_v2_resumeSession,
  unstable_v2_prompt
} from "@anthropic-ai/claude-agent-sdk";

// Create a new session
const session = await unstable_v2_createSession({
  model: "claude-sonnet-4-5",
  workingDirectory: process.cwd(),
  allowedTools: ["Read", "Grep", "Glob"]
});

// Send prompts and stream responses
const stream = unstable_v2_prompt(session, "Analyze the codebase structure");
for await (const message of stream) {
  console.log(message);
}

// Continue conversation in same session
const stream2 = unstable_v2_prompt(session, "Now suggest improvements");
for await (const message of stream2) {
  console.log(message);
}

// Resume a previous session
const resumedSession = await unstable_v2_resumeSession(session.sessionId);

Note: V2 APIs are in preview (unstable_ prefix). The .receive() method was renamed to .stream() in v0.1.72.

Permission Control

Permission Modes:

type PermissionMode = "default" | "acceptEdits" | "bypassPermissions" | "plan";

default - Standard permission checks
acceptEdits - Auto-approve file edits
bypassPermissions - Skip ALL checks (use in CI/CD only)
plan - Planning mode (v0.1.45+)

Custom Permission Logic

const response = query({
  prompt: "Deploy application to production",
  options: {
    permissionMode: "default",
    canUseTool: async (toolName, input) => {
      // Allow read-only operations
      if (['Read', 'Grep', 'Glob'].includes(toolName)) {
        return { behavior: "allow" };
      }

      // Deny destructive bash commands
      if (toolName === 'Bash') {
        const dangerous = ['rm -rf', 'dd if=', 'mkfs', '> /dev/'];
        if (dangerous.some(pattern => input.command.includes(pattern))) {
          return {
            behavior: "deny",
            message: "Destructive command blocked for safety"
          };
        }
      }

      // Require confirmation for deployments
      if (input.command?.includes('deploy') || input.command?.includes('kubectl apply')) {
        return {
          behavior: "ask",
          message: "Confirm deployment to production?"
        };
      }

      // Allow by default
      return { behavior: "allow" };
    }
  }
});

canUseTool Callback

type CanUseToolCallback = (
  toolName: string,
  input: any
) => Promise<PermissionDecision>;

type PermissionDecision =
  | { behavior: "allow" }
  | { behavior: "deny"; message?: string }
  | { behavior: "ask"; message?: string };

Examples:

// Block all file writes
canUseTool: async (toolName, input) => {
  if (toolName === 'Write' || toolName === 'Edit') {
    return { behavior: "deny", message: "No file modifications allowed" };
  }
  return { behavior: "allow" };
}

// Require confirmation for specific files
canUseTool: async (toolName, input) => {
  const sensitivePaths = ['/etc/', '/root/', '.env', 'credentials.json'];
  if ((toolName === 'Write' || toolName === 'Edit') &&
      sensitivePaths.some(path => input.file_path?.includes(path))) {
    return {
      behavior: "ask",
      message: `Modify sensitive file ${input.file_path}?`
    };
  }
  return { behavior: "allow" };
}

// Log all tool usage
canUseTool: async (toolName, input) => {
  console.log(`Tool requested: ${toolName}`, input);
  await logToDatabase(toolName, input);
  return { behavior: "allow" };
}

Sandbox Settings (Security-Critical)

Enable sandboxed execution for Bash commands:

const response = query({
  prompt: "Run system diagnostics",
  options: {
    sandbox: {
      enabled: true,
      autoAllowBashIfSandboxed: true,  // Auto-approve bash in sandbox
      excludedCommands: ["rm", "dd", "mkfs"],  // Never auto-approve these
      allowUnsandboxedCommands: false  // Deny unsandboxable commands
    }
  }
});

SandboxSettings Type

type SandboxSettings = {
  enabled: boolean;
  autoAllowBashIfSandboxed?: boolean;  // Default: false
  excludedCommands?: string[];
  allowUnsandboxedCommands?: boolean;  // Default: false
  network?: NetworkSandboxSettings;
  ignoreViolations?: SandboxIgnoreViolations;
};

type NetworkSandboxSettings = {
  enabled: boolean;
  proxyUrl?: string;  // HTTP proxy for network requests
};

Key Options:

enabled - Activate sandbox isolation
autoAllowBashIfSandboxed - Skip permission prompts for safe bash commands
excludedCommands - Commands that always require permission
allowUnsandboxedCommands - Allow commands that can't be sandboxed (risky)
network.proxyUrl - Route network through proxy for monitoring

Best Practice: Always use sandbox in production agents handling untrusted input.

File Checkpointing

Enable file state snapshots for rollback capability:

const response = query({
  prompt: "Refactor the authentication module",
  options: {
    enableFileCheckpointing: true  // Enable file snapshots
  }
});

// Later: rewind file changes to a specific point
for await (const message of response) {
  if (message.type === 'user' && message.uuid) {
    // Can rewind to this point later
    const userMessageUuid = message.uuid;

    // To rewind (call on Query object)
    await response.rewindFiles(userMessageUuid);
  }
}

Use cases:

Undo failed refactoring attempts
A/B test code changes
Safe exploration of alternatives

Filesystem Settings

Setting Sources:

type SettingSource = 'user' | 'project' | 'local';

user - ~/.claude/settings.json (global)
project - .claude/settings.json (team-shared)
local - .claude/settings.local.json (gitignored overrides)

Default: NO settings loaded (settingSources: [])

Settings Priority

When multiple sources loaded, settings merge in this order (highest priority first):

Programmatic options (passed to query()) - Always win
Local settings (.claude/settings.local.json)
Project settings (.claude/settings.json)
User settings (~/.claude/settings.json)

Example:

// .claude/settings.json
{
  "allowedTools": ["Read", "Write", "Edit"]
}

// .claude/settings.local.json
{
  "allowedTools": ["Read"]  // Overrides project settings
}

// Programmatic
const response = query({
  options: {
    settingSources: ["project", "local"],
    allowedTools: ["Read", "Grep"]  // ← This wins
  }
});

// Actual allowedTools: ["Read", "Grep"]

Best Practice: Use settingSources: ["project"] in CI/CD for consistent behavior.

Query Object Methods

The query() function returns a Query object with these methods:

const q = query({ prompt: "..." });

// Async iteration (primary usage)
for await (const message of q) { ... }

// Runtime model control
await q.setModel("claude-opus-4-5");           // Change model mid-session
await q.setMaxThinkingTokens(4096);            // Set thinking budget

// Introspection
const models = await q.supportedModels();     // List available models
const commands = await q.supportedCommands(); // List available commands
const account = await q.accountInfo();        // Get account details

// MCP status
const status = await q.mcpServerStatus();     // Check MCP server status
// Returns: { [serverName]: { status: 'connected' | 'failed', error?: string } }

// File operations (requires enableFileCheckpointing)
await q.rewindFiles(userMessageUuid);         // Rewind to checkpoint

Use cases:

Dynamic model switching based on task complexity
Monitoring MCP server health
Adjusting thinking budget for reasoning tasks

Message Types & Streaming

Message Types:

system - Session init/completion (includes session_id)
assistant - Agent responses
tool_call - Tool execution requests
tool_result - Tool execution results
error - Error messages
result - Final result (includes structured_output for v0.1.45+)

Streaming Pattern:

for await (const message of response) {
  if (message.type === 'system' && message.subtype === 'init') {
    sessionId = message.session_id;  // Capture for resume/fork
  }
  if (message.type === 'result' && message.structured_output) {
    // Structured output available (v0.1.45+)
    const validated = schema.parse(message.structured_output);
  }
}

Error Handling

Error Codes:

Error Code	Cause	Solution
`CLI_NOT_FOUND`	Claude Code not installed	Install: `npm install -g @anthropic-ai/claude-code`
`AUTHENTICATION_FAILED`	Invalid API key	Check ANTHROPIC_API_KEY env var
`RATE_LIMIT_EXCEEDED`	Too many requests	Implement retry with backoff
`CONTEXT_LENGTH_EXCEEDED`	Prompt too long	Use session compaction, reduce context
`PERMISSION_DENIED`	Tool blocked	Check permissionMode, canUseTool
`TOOL_EXECUTION_FAILED`	Tool error	Check tool implementation
`SESSION_NOT_FOUND`	Invalid session ID	Verify session ID
`MCP_SERVER_FAILED`	Server error	Check server configuration

Known Issues Prevention

This skill prevents 14 documented issues:

Issue #1: CLI Not Found Error

Error: "Claude Code CLI not installed" Source: SDK requires Claude Code CLI Why It Happens: CLI not installed globally Prevention: Install before using SDK: npm install -g @anthropic-ai/claude-code

Issue #2: Authentication Failed

Error: "Invalid API key" Source: Missing or incorrect ANTHROPIC_API_KEY Why It Happens: Environment variable not set Prevention: Always set export ANTHROPIC_API_KEY="sk-ant-..."

Issue #3: Permission Denied Errors

Error: Tool execution blocked Source: permissionMode restrictions Why It Happens: Tool not allowed by permissions Prevention: Use allowedTools or custom canUseTool callback

Issue #4: Context Length Exceeded (Session-Breaking)

Error: "Prompt too long" Source: Input exceeds model context window (Issue #138) Why It Happens: Large codebase, long conversations

⚠️ Critical Behavior: Once a session hits context limit:

All subsequent requests to that session return "Prompt too long"
/compact command fails with same error
Session is permanently broken and must be abandoned

Prevention Strategies:

// 1. Proactive session forking (create checkpoints before hitting limit)
const checkpoint = query({
  prompt: "Checkpoint current state",
  options: {
    resume: sessionId,
    forkSession: true  // Create branch before hitting limit
  }
});

// 2. Monitor time and rotate sessions proactively
const MAX_SESSION_TIME = 80 * 60 * 1000;  // 80 minutes (before 90-min crash)
let sessionStartTime = Date.now();

function shouldRotateSession() {
  return Date.now() - sessionStartTime > MAX_SESSION_TIME;
}

// 3. Start new sessions before hitting context limits
if (shouldRotateSession()) {
  const summary = await getSummary(currentSession);
  const newSession = query({
    prompt: `Continue with context: ${summary}`
  });
  sessionStartTime = Date.now();
}

Note: SDK auto-compacts, but if limit is reached, session becomes unrecoverable

Issue #5: Tool Execution Timeout

Error: Tool doesn't respond Source: Long-running tool execution Why It Happens: Tool takes too long (>5 minutes default) Prevention: Implement timeout handling in tool implementations

Issue #6: Session Not Found

Error: "Invalid session ID" Source: Session expired or invalid Why It Happens: Session ID incorrect or too old Prevention: Capture session_id from system init message

Issue #7: MCP Server Connection Failed

Error: Server not responding Source: Server not running or misconfigured Why It Happens: Command/URL incorrect, server crashed Prevention: Test MCP server independently, verify command/URL

Issue #8: Subagent Definition Errors

Error: Invalid AgentDefinition Source: Missing required fields Why It Happens: description or prompt missing Prevention: Always include description and prompt fields

Issue #9: Settings File Not Found

Error: "Cannot read settings" Source: Settings file doesn't exist Why It Happens: settingSources includes non-existent file Prevention: Check file exists before including in sources

Issue #10: Tool Name Collision

Error: Duplicate tool name Source: Multiple tools with same name Why It Happens: Two MCP servers define same tool name Prevention: Use unique tool names, prefix with server name

Issue #11: Zod Schema Validation Error

Error: Invalid tool input Source: Input doesn't match Zod schema Why It Happens: Agent provided wrong data type Prevention: Use descriptive Zod schemas with .describe()

Issue #12: Filesystem Permission Denied

Error: Cannot access path Source: Restricted filesystem access Why It Happens: Path outside workingDirectory or no permissions Prevention: Set correct workingDirectory, check file permissions

Issue #13: MCP Server Config Missing `type` Field

Error: "Claude Code process exited with code 1" (cryptic, no context) Source: GitHub Issue #131 Why It Happens: URL-based MCP servers require explicit type: "http" or type: "sse" field Prevention: Always specify transport type for URL-based MCP servers

// ❌ Wrong - missing type field (causes cryptic exit code 1)
mcpServers: {
  "my-server": {
    url: "https://api.example.com/mcp"
  }
}

// ✅ Correct - type field required for URL-based servers
mcpServers: {
  "my-server": {
    url: "https://api.example.com/mcp",
    type: "http"  // or "sse" for Server-Sent Events
  }
}

Diagnostic Clue: If you see "process exited with code 1" with no other context, check your MCP server configuration for missing type fields.

Issue #14: MCP Tool Result with Unicode Line Separators

Error: JSON parse error, agent hangs Source: GitHub Issue #137 Why It Happens: Unicode U+2028 (line separator) and U+2029 (paragraph separator) are valid in JSON but break JavaScript parsing Prevention: Escape these characters in MCP tool results

// MCP tool handler - sanitize external data
tool("fetch_content", "Fetch text content", {}, async (args) => {
  const content = await fetchExternalData();

  // ✅ Sanitize Unicode line/paragraph separators
  const sanitized = content
    .replace(/\u2028/g, '\\u2028')
    .replace(/\u2029/g, '\\u2029');

  return {
    content: [{ type: "text", text: sanitized }]
  };
});

When This Matters: External data sources (APIs, web scraping, user input) that may contain these characters

Related: MCP Python SDK Issue #1356

Official Documentation

Agent SDK Overview: https://platform.claude.com/docs/en/api/agent-sdk/overview
TypeScript API: https://platform.claude.com/docs/en/api/agent-sdk/typescript
Structured Outputs: https://platform.claude.com/docs/en/agent-sdk/structured-outputs
GitHub (TypeScript): https://github.com/anthropics/claude-agent-sdk-typescript
CHANGELOG: https://github.com/anthropics/claude-agent-sdk-typescript/blob/main/CHANGELOG.md

Token Efficiency:

Without skill: ~15,000 tokens (MCP setup, permission patterns, session APIs, sandbox config, hooks, structured outputs, error handling)
With skill: ~4,500 tokens (comprehensive v0.2.12 coverage + error prevention + advanced patterns)
Savings: ~70% (~10,500 tokens)

Errors prevented: 14 documented issues with exact solutions (including 2 community-sourced gotchas) Key value: V2 Session APIs, Sandbox Settings, File Checkpointing, Query methods, AskUserQuestion tool, structured outputs (v0.1.45+), session forking, canUseTool patterns, complete hooks system (12 events), Zod v4 support, subagent cleanup patterns

Last verified: 2026-01-20 | Skill version: 3.1.0 | Changes: Added Issue #13 (MCP type field), Issue #14 (Unicode U+2028/U+2029), expanded Issue #4 (session-breaking), added subagent cleanup warning with Stop hook pattern

claude-agent-sdk

Claude Agent SDK - Structured Outputs & Error Prevention Guide

What's New in v0.1.45+ (Nov 2025)

1. Structured Outputs (v0.1.45, Nov 14, 2025)

2. Plugins System (v0.1.27)

3. Hooks System (v0.1.0+)

4. Additional Options

The Complete Claude Agent SDK Reference

Table of Contents

Core Query API

Extended Context (1M Tokens)

System Prompt Configuration

Tool Integration (Built-in + Custom)

AskUserQuestion Tool (v0.1.71+)

Tools Configuration (v0.1.57+)

MCP Servers (Model Context Protocol)

External MCP Servers (stdio)

External MCP Servers (HTTP/SSE)

MCP Tool Naming Convention

Subagent Orchestration

AgentDefinition Type

⚠️ Subagent Cleanup Warning

Session Management

V2 Session APIs (Preview - v0.1.54+)

Permission Control

Custom Permission Logic

canUseTool Callback

Sandbox Settings (Security-Critical)

SandboxSettings Type

File Checkpointing

Filesystem Settings

Settings Priority

Query Object Methods

Message Types & Streaming

Error Handling

Known Issues Prevention

Issue #1: CLI Not Found Error

Issue #2: Authentication Failed

Issue #3: Permission Denied Errors

Issue #4: Context Length Exceeded (Session-Breaking)

Issue #5: Tool Execution Timeout

Issue #6: Session Not Found

Issue #7: MCP Server Connection Failed

Issue #8: Subagent Definition Errors

Issue #9: Settings File Not Found

Issue #10: Tool Name Collision

Issue #11: Zod Schema Validation Error

Issue #12: Filesystem Permission Denied

Issue #13: MCP Server Config Missing type Field

Issue #14: MCP Tool Result with Unicode Line Separators

Official Documentation

Issue #13: MCP Server Config Missing `type` Field