Configure Cedar policy enforcement and Ed25519 signed receipts for Claude Code tool calls. Use when setting up projects that need cryptographic audit trails, policy-gated tool execution, or compliance-ready evidence of agent actions.
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.
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:
npx @veritasacta/verify. No server, no account,
no trust in the operator.AI agents make decisions that affect money, safety, and rights. The Claude Code session log records what happened, but the log is:
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.
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/
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/"
}
}
]
}
}
PreToolUse — Runs BEFORE the tool executes. Evaluates the tool call against
your Cedar policy file. If Cedar returns deny, the hook exits with code 2 and
Claude Code blocks the tool call entirely.
PostToolUse — Runs AFTER the tool completes. Signs a receipt containing the
tool name, input hash, output hash, decision, policy digest, and timestamp.
Writes the receipt to ./receipts/<timestamp>.json.
Create ./protect.cedar at the project root:
// Allow read-only tools by default
permit (
principal,
action in [Action::"Read", Action::"Glob", Action::"Grep", Action::"WebFetch"],
resource
);
// Require explicit allow for destructive tools
permit (
principal,
action == Action::"Bash",
resource
) when {
// Allow safe commands only
context.command_pattern in ["git", "npm", "ls", "cat", "echo", "pwd", "test"]
};
// Never allow recursive deletion
forbid (
principal,
action == Action::"Bash",
resource
) when {
context.command_pattern == "rm -rf"
};
// Require confirmation for writes outside the project
forbid (
principal,
action in [Action::"Edit", Action::"Write"],
resource
) when {
context.path_starts_with != "."
};
Verify a single receipt:
npx @veritasacta/verify receipts/2026-04-15T10-30-00Z.json
# Exit 0 = valid
# Exit 1 = tampered
# Exit 2 = malformed
Verify the entire chain:
npx @veritasacta/verify receipts/*.json
Use the plugin's slash commands from within Claude Code:
/verify-receipt receipts/latest.json
/audit-chain ./receipts/ --last 20
Each receipt is a JSON file with this structure:
{
"receipt_id": "rec_8f92a3b1",
"receipt_version": "1.0",
"issuer_id": "claude-code-protect-mcp",
"event_time": "2026-04-15T10:30:00.000Z",
"tool_name": "Bash",
"input_hash": "sha256:a3f8...",
"decision": "allow",
"policy_id": "autoresearch-safe",
"policy_digest": "sha256:b7e2...",
"parent_receipt_id": "rec_3d1ab7c2",
"public_key": "4437ca56815c0516...",
"signature": "4cde814b7889e987..."
}
parent_receipt_id| Before | After |
|---|---|
| "Trust me, the agent only read files" | Cryptographically provable: every Read logged and signed |
| "The log shows it happened" | The receipt proves it happened, and no one can edit it |
| "You'd have to audit our system" | Anyone can verify every receipt offline |
| "Logs might be different by now" | Ed25519 signatures lock the record at signing time |