Claude Code v2.1.63 ships a significant change to how you hook into the agent lifecycle: shell-based hooks are out, HTTP webhooks are in. If you’ve been using hooks in your Claude Code pipeline, this guide walks through the migration and shows you why the new pattern is worth the effort.

Why HTTP Hooks?

The old shell hook model had a fundamental problem: crossing the shell boundary destroyed structure. You serialized data to a string, passed it through a shell command, and parsed it back out on the other side. Every step introduced escaping issues, subprocess overhead, and opportunities for silent failure.

HTTP hooks replace that with a clean JSON-over-HTTP round-trip:

  • Claude Code POSTs structured JSON to your endpoint
  • Your endpoint receives typed, parseable data
  • You return JSON, Claude Code ingests it directly

No shell escaping. No subprocess. No string-parsing. Your hook endpoint can be a local server, a cloud function, or anything that speaks HTTP.

Prerequisites

  • Claude Code v2.1.63 or later (claude --version)
  • A local or accessible HTTP endpoint (we’ll build one below)
  • Node.js or Python for the example server

Step 1: Stand Up a Simple Hook Server

Here’s a minimal Python hook server using FastAPI:

from fastapi import FastAPI, Request
import uvicorn
import json

app = FastAPI()

@app.post("/hook/pre-tool")
async def pre_tool_hook(request: Request):
    payload = await request.json()
    print(f"[HOOK] pre-tool: {json.dumps(payload, indent=2)}")
    
    # Return modified context or pass-through
    return {
        "action": "continue",
        "metadata": {
            "hook_processed": True,
            "timestamp": "2026-03-01T20:09:00Z"
        }
    }

@app.post("/hook/post-tool")
async def post_tool_hook(request: Request):
    payload = await request.json()
    print(f"[HOOK] post-tool: {json.dumps(payload, indent=2)}")
    return {"action": "continue"}

if __name__ == "__main__":
    uvicorn.run(app, host="127.0.0.1", port=8765)

Run it:

pip install fastapi uvicorn
python hook_server.py

Step 2: Configure Claude Code HTTP Hooks

In your .claude/config.json (or wherever your Claude Code config lives), replace any shell hook definitions with HTTP hook entries:

{
  "hooks": {
    "pre-tool": {
      "type": "http",
      "url": "http://127.0.0.1:8765/hook/pre-tool",
      "timeout_ms": 5000
    },
    "post-tool": {
      "type": "http",
      "url": "http://127.0.0.1:8765/hook/post-tool",
      "timeout_ms": 5000
    }
  }
}

The timeout_ms field is important — Claude Code will wait up to this duration for your hook to respond before proceeding.

Step 3: Understand the Payload Schema

Claude Code sends structured JSON to each hook. A pre-tool payload looks roughly like:

{
  "event": "pre-tool",
  "tool": {
    "name": "bash",
    "input": {
      "command": "ls -la"
    }
  },
  "context": {
    "session_id": "abc123",
    "turn": 4
  }
}

Your hook receives this, can inspect or modify behavior, and returns a response. Return {"action": "continue"} to proceed normally, or {"action": "block", "reason": "..."} to halt the tool call.

Step 4: Handle the ENABLE_CLAUDEAI_MCP_SERVERS Flag

v2.1.63 also introduces an environment variable to control claude.ai MCP server loading:

export ENABLE_CLAUDEAI_MCP_SERVERS=false

Set this in your shell or .env if you want Claude Code to skip auto-loading claude.ai MCP servers — useful for air-gapped environments or when you want deterministic MCP configurations.

Step 5: Migrate Existing Shell Hooks

If you had shell hooks like:

# Old shell hook (pre-2.1.63)
"pre-tool": "echo '$CLAUDE_HOOK_PAYLOAD' | python3 my_hook.py"

Your migration path:

  1. Extract the logic from my_hook.py into a proper HTTP handler
  2. Point the HTTP hook at http://localhost:<port>/your-endpoint
  3. Update the return format from stdout text to JSON response body

The payload schema is cleaner than environment variable injection — take the migration as an opportunity to improve your hook logic, not just port it.

Practical Patterns

Audit logging: Every tool call hits your hook → log to JSONL for full auditability of what Claude Code executed and when.

Rate limiting: Pre-tool hook tracks call frequency → returns block if a tool is being called too aggressively in a session.

Secret injection: Pre-tool hook injects environment-specific secrets into bash commands without storing them in config files.

Notification: Post-tool hook fires webhooks to Slack/Discord when long-running operations complete.

Verifying It Works

With your hook server running and Claude Code configured, start a session and watch your server logs. You should see POST requests arriving with tool call data before and after each tool execution. If you see nothing, double-check the url in your config and that the server is listening on the right port.

Sources

  1. Claude Code v2.1.63 Changelog — claudefa.st
  2. GitHub Issue #29504 — anthropics/claude-code

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