protect-mcp-setup

protect-mcp — Policy Enforcement + Signed Receipts

Cryptographic governance for every Claude Code tool call. Each invocation is evaluated against a Cedar policy and produces an Ed25519-signed receipt that anyone can verify offline.

Overview

Claude Code runs powerful tools: Bash, Edit, Write, WebFetch. By default there is no audit trail, no policy enforcement, and no way to prove what was decided after the fact. protect-mcp closes all three gaps:

• Cedar policies (AWS's open authorization engine) evaluate every tool call before execution. Cedar deny is authoritative.
• Ed25519 receipts record each decision with its inputs, the policy that governed it, and the outcome. Receipts are hash-chained.
• Offline verification via npx @veritasacta/verify. No server, no account, no trust in the operator.

Problem

AI agents make decisions that affect money, safety, and rights. The Claude Code session log records what happened, but the log is:

• Mutable — anyone with access can edit it
• Unsigned — there is no way to prove integrity
• Operator-bound — verification requires trusting whoever holds the log

For compliance contexts (finance, healthcare, regulated research), this is not sufficient. You need tamper-evident evidence that can be verified by third parties without trusting you.

Solution

Add protect-mcp to your Claude Code project:

# 1. Install the plugin (adds hooks + skill to your project)
claude plugin install wshobson/agents/protect-mcp

# 2. Configure hooks in .claude/settings.json (see below)

# 3. Start the receipt-signing server (runs locally, no external calls)
npx protect-mcp@latest serve --enforce

# 4. Use Claude Code normally. Every tool call is now policy-evaluated
#    and produces a signed receipt in ./receipts/

Hook Configuration

Add the following to your project's .claude/settings.json:

{
  "hooks": {
    "PreToolUse": [
      {
        "matcher": ".*",
        "hook": {
          "type": "command",
          "command": "npx protect-mcp@latest evaluate --policy ./protect.cedar --tool \"$TOOL_NAME\" --input \"$TOOL_INPUT\" || exit 2"
        }
      }
    ],
    "PostToolUse": [
      {
        "matcher": ".*",
        "hook": {
          "type": "command",
          "command": "npx protect-mcp@latest sign --tool \"$TOOL_NAME\" --input \"$TOOL_INPUT\" --output \"$TOOL_OUTPUT\" --receipts ./receipts/"
        }
      }
    ]
  }
}