Slash Commands in Claude Agent SDK Sessions

Overview

Slash commands control a Claude Agent SDK session with special / commands. Only commands that work without an interactive terminal are dispatchable through the SDK; the system init message lists the ones available in your session.

Discover available commands

for await (const message of query({ prompt: "Hello", options: { maxTurns: 1 } })) {
  if (message.type === "system" && message.subtype === "init") {
    console.log("Available slash commands:", message.slash_commands);
    // e.g. ["clear", "compact", "context", "usage"]
  }
}

Send a command

Send a slash command by putting it in the prompt string:

for await (const message of query({ prompt: "/compact", options: { maxTurns: 1 } })) {
  if (message.type === "result" && message.subtype === "success") {
    console.log("Command executed:", message.result);
  }
}

Common built-ins include /compact (summarize history; emits a compact_boundary system message with pre_tokens) and /clear (reset context; useful in streaming-input mode, requires v2.1.117+). For one-shot query() calls /clear has no effect since each call starts empty.

Define custom commands

Custom commands are markdown files; the filename becomes the command name. The recommended format is .claude/skills/<name>/SKILL.md (which also supports autonomous invocation); .claude/commands/ is the legacy format and still works.

---
allowed-tools: Read, Grep, Glob
description: Run security vulnerability scan
---

Analyze the codebase for security vulnerabilities including SQL injection,
XSS, exposed credentials, and insecure configurations.

Custom commands support arguments ($0, $1, $ARGUMENTS), embedded bash output (!`git status`), and file references (@package.json). They appear in the slash_commands list and are invoked like built-ins:

for await (const message of query({ prompt: "/security-check", options: { maxTurns: 3 } })) {
  /* ... */
}

Organization

Group commands in subdirectories (for example .claude/commands/frontend/); the subdirectory shows in the description but not the command name.

Source

• Slash Commands in the SDK: https://code.claude.com/docs/en/agent-sdk/slash-commands