How I built a trust scoring hook for Claude Code

I've been using Claude Code for a while and realized I had zero visibility into what the agent was doing across sessions. Which tools it called, whether it touched files it shouldn't have, how many calls it made per task.

So I built a hook that scores every session.

What it does

The hook listens to three Claude Code events:

• PostToolUse — records every tool call, checks it against an allowlist, flags protected path access
• PreToolUse — blocks tool calls that touch sensitive files like .env or SSH keys
• Stop — computes the final trust score and logs it

At the end of each session you get:

[authe.me] Trust Score: 92 (reliability=100 | scope=75 | cost=100)
[authe.me] tools=14 violations=1 failed=0

The scoring

Three dimensions, weighted into an overall score:

• Reliability (40%) — what percentage of tool calls succeeded
• Scope (35%) — did the agent stay within your allowed tools and paths. Each violation drops the score by 25 points
• Cost (25%) — how many tool calls were made. Under 20 is fine, over 100 starts flagging

Hash chaining

Every tool call event gets hashed with the previous hash, creating a chain. If someone tampers with the log, the chain breaks. Same concept as blockchain audit trails but much simpler.

def compute_hash(prev_hash, data):
    payload = f"{prev_hash}:{json.dumps(data, sort_keys=True)}"
    return hashlib.sha256(payload.encode()).hexdigest()[:16]

Protected path blocking

The PreToolUse hook checks if Claude is about to read or edit a sensitive file. If it matches, the hook returns a deny decision with a reason that Claude receives as feedback:

result = {
    "hookSpecificOutput": {
        "hookEventName": "PreToolUse",
        "permissionDecision": "deny",
        "permissionDecisionReason": "authe.me policy: .env is a protected path."
    }
}

Claude sees the denial reason and adjusts its plan.

Install

mkdir -p ~/.claude/hooks ~/.authe
curl -fsSL https://raw.githubusercontent.com/autheme/claude-code-hook/main/authe-hook.py -o ~/.claude/hooks/authe-hook.py
chmod +x ~/.claude/hooks/authe-hook.py

Then add the hook config to ~/.claude/settings.json:

{
  "hooks": {
    "PostToolUse": [
      {
        "matcher": "",
        "hooks": [
          {
            "type": "command",
            "command": "AUTHE_HOOK_EVENT=PostToolUse python3 ~/.claude/hooks/authe-hook.py"
          }
        ]
      }
    ],
    "Stop": [
      {
        "matcher": "",
        "hooks": [
          {
            "type": "command",
            "command": "AUTHE_HOOK_EVENT=Stop python3 ~/.claude/hooks/authe-hook.py"
          }
        ]
      }
    ]
  }
}

Single file, zero dependencies, pure Python.

What's next

Working on remote reporting so you can aggregate scores across sessions and agents. Also building an OpenClaw plugin that does the same thing for that ecosystem.

Repo: github.com/autheme/claude-code-hook

Built with Claude. Would love feedback from anyone running Claude Code in production.