Sensitive Canary

A security plugin that prevents unintended data leaks from Claude Code. Automatically detects and blocks secrets and PII — in prompts, file reads, and command executions — before they are sent to the Anthropic API.

No proxy server. No background process. Native Claude Code hooks only.

📖 Documentation — Installation guide, detection rules reference, and allow tag details.

Why sensitive-canary?

Claude Code is a powerful development tool, but file reads and command executions can inadvertently send secrets and personal information to the Anthropic API. API keys in .env files, tokens embedded in config files, credentials pasted into the terminal — once sent to the API, they leave your machine.

sensitive-canary intercepts them before they are sent, preventing unintended data leaks.

Without sensitive-canary	With sensitive-canary
`cat .env` → full contents sent to Claude ❌	Blocked by name before Claude reads it ✅
Paste `AKIAIOSFODNN7EXAMPLE` in prompt ❌	Blocked before the API call is made ✅
Tool result contains [email protected] ❌	PII detected and blocked ✅
`echo $API_KEY` with live key ❌	Env var value scanned and blocked ✅

Two hooks — UserPromptSubmit and PreToolUse cover both directions of risk
31 detection rules — sourced from gitleaks and TruffleHog detector definitions
Entropy filtering — reduces false positives on low-entropy values
Luhn validation — credit card numbers are validated, not just pattern-matched
Local only — all scanning runs in your terminal; nothing is sent anywhere

Quick Start

Requirements

Node.js 22.6.0 or later (required for --experimental-strip-types)
Claude Code 1.0.33 or later

Plugin install (recommended)

Install in two commands from inside a Claude Code session:

1. Register the marketplace

/plugin marketplace add coo-quack/claude-code-marketplace

2. Install the plugin

/plugin install sensitive-canary@coo-quack

Done. The hooks are enabled automatically.

Keeping up to date: Third-party marketplaces have auto-update disabled by default. To receive automatic updates, run /plugin → Marketplaces tab → select the marketplace → Enable auto-update. You can also update manually from the same tab. See Discover and install plugins for details.

npm install

Install locally via npm and configure hooks manually:

npm install -g @coo-quack/sensitive-canary

Update to the latest version:

npm update -g @coo-quack/sensitive-canary

Then add to ~/.claude/settings.json:

{
  "hooks": {
    "UserPromptSubmit": [
      {
        "hooks": [
          {
            "type": "command",
            "command": "npx tsx $(npm root -g)/@coo-quack/sensitive-canary/src/user-prompt-submit-hook.ts"
          }
        ]
      }
    ],
    "PreToolUse": [
      {
        "matcher": "Read|Bash",
        "hooks": [
          {
            "type": "command",
            "command": "npx tsx $(npm root -g)/@coo-quack/sensitive-canary/src/pre-tool-use-hook.ts"
          }
        ]
      }
    ]
  }
}

Note: Node.js does not support --experimental-strip-types for files inside node_modules, so npx tsx is used instead.

Manual setup (git clone)

Clone the repository and configure hooks manually:

git clone https://github.com/coo-quack/sensitive-canary.git ~/sensitive-canary

Update to the latest version:

cd ~/sensitive-canary && git pull

Then add to ~/.claude/settings.json:

{
  "hooks": {
    "UserPromptSubmit": [
      {
        "hooks": [
          {
            "type": "command",
            "command": "node --experimental-strip-types ~/sensitive-canary/src/user-prompt-submit-hook.ts"
          }
        ]
      }
    ],
    "PreToolUse": [
      {
        "matcher": "Read|Bash",
        "hooks": [
          {
            "type": "command",
            "command": "node --experimental-strip-types ~/sensitive-canary/src/pre-tool-use-hook.ts"
          }
        ]
      }
    ]
  }
}

What Happens

Prompt blocked

Prompts containing secrets or PII are blocked before being sent.

> My AWS key is AKIAIOSFODNN7EXAMPLE. Can you review this code?

🐤  sensitive-canary: sensitive data detected — blocked

  [Secret] AWS Access Key ID (aws-access-key): AKIA****MPLE

To allow, add a tag to your prompt:
  [allow-secret]  — allow secrets
  [allow-all]     — bypass all sensitive-canary checks

To allow it through, add the suggested tag:

> [allow-secret] My AWS key is AKIAIOSFODNN7EXAMPLE. Can you review this code?

.env file blocked

.env / .env.* files are blocked unconditionally, regardless of their contents.

> Read .env

🐤 sensitive-canary: blocked — /path/to/.env

🚫 Blocked: .env and .env.* files contain secrets and must not be read into the conversation.

To allow this, the user must add an allow tag to their next prompt:
  [allow-secret]  — allow secrets
  [allow-pii]     — allow PII
  [allow-all]     — bypass all sensitive-canary checks

Example: "[allow-secret] please read /path/to/.env"

File content blocked

Non-.env files are also blocked if their contents contain secrets or PII.

> Read config.yaml

🐤 sensitive-canary: blocked — /path/to/config.yaml

🚫 Blocked: file contains sensitive data

  [Secret] AWS Access Key ID (aws-access-key): AKIA****MPLE

Allow tags

To intentionally bypass a block, include the appropriate tag in your current prompt.

Tag	Effect
`[allow-secret]`	Skip all secret-category checks
`[allow-pii]`	Skip all PII-category checks
`[allow-all]`	Skip all sensitive-canary checks

Note: Tags are read from the current user message only. Tags in previous messages are ignored — there is no risk of an accidental persistent bypass. Tags are case-insensitive. [allow-secret] does not bypass PII blocks (and vice versa). The name-based block on .env/.env.* files can be bypassed by any of the three allow tags.

Detection rules

Secrets (24 rules)

Rule ID	Description
`aws-access-key`	AWS Access Key ID
`gcp-api-key`	Google Cloud API Key
`private-key`	PEM Private Key (RSA / EC / DSA / PGP / OpenSSH)
`github-pat`	GitHub Personal Access Token
`github-fine-grained`	GitHub Fine-Grained Token
`gitlab-pat`	GitLab Personal Access Token
`npm-token`	npm Access Token
`slack-token`	Slack Token
`slack-webhook`	Slack Webhook URL
`discord-webhook`	Discord Webhook URL
`telegram-bot-token`	Telegram Bot Token
`twilio-sid`	Twilio Account SID
`sendgrid-key`	SendGrid API Key
`mailgun-key`	Mailgun API Key
`mailchimp-key`	Mailchimp API Key
`stripe-secret-key`	Stripe Secret Key
`stripe-restricted-key`	Stripe Restricted Key
`openai-key`	OpenAI API Key (legacy format)
`openai-project-key`	OpenAI Project API Key (`sk-proj-` prefix) (entropy ≥ 3.5)
`anthropic-key`	Anthropic API Key
`jwt`	JSON Web Token (JWT)
`generic-secret`	Generic API key / secret assignment (entropy ≥ 3.5)
`env-assignment`	`.env`-style secret assignment (entropy ≥ 3.0)
`connection-string`	Database connection string with embedded credentials

PII (7 rules)

Rule ID	Description	Validation
`pii-email`	Email address	—
`pii-credit-card`	Credit card number	Luhn check
`pii-ssn`	US Social Security Number	Invalid prefix exclusion
`pii-phone-us`	US phone number	—
`pii-phone-jp`	Japanese phone number	—
`pii-postal-jp`	Japanese postal code (`〒` prefix required)	—
`pii-ipv4`	IPv4 address (RFC 1918 private ranges only)	—

Detection patterns are based on rule definitions from gitleaks and TruffleHog.

How It Works

① UserPromptSubmit hook

Runs just before a prompt is sent to the API.

User presses Enter
      ↓
UserPromptSubmit hook
      ↓ scans prompt
      ├─ secret / PII detected AND no matching [allow-xxx] tag → block (exit 2)
      └─ nothing detected OR tag present → pass (exit 0)

When blocked, the terminal shows what was detected and how to bypass it.

② PreToolUse hook

Runs just before Claude calls the Read or Bash tool.

Claude calls Read / Bash tool
      ↓
PreToolUse hook
      ↓
      ── Read tool ─────────────────────────────────────────────────────
      │  1. filename is .env / .env.* → blocked unconditionally
      │  2. file contents contain secret / PII → blocked
      └─ Bash tool ─────────────────────────────────────────────────────
         1. env var values referenced in the command contain secret / PII → blocked
         2. command string itself contains secret / PII (e.g. echo AKIA...) → blocked
         3. cat / head / tail / etc. targeting a file → file contents scanned

When blocked, Claude receives a JSON response explaining the reason and is prompted to tell the user.
The terminal also receives a direct message (via /dev/tty).

Allow Tags (detailed)

Allow tags filter the scan results — the scan itself always runs. The .env/.env.* name block is the only exception: when an allow tag is present, the file is passed through immediately without scanning.

Mask tags

[mask-secret], [mask-pii], and [mask-all] are recognised but not supported. Claude Code hooks cannot rewrite prompt content, so masking before sending is not possible.

If you include a mask tag, sensitive-canary will explain this and list what was detected:

> [mask-secret] My key is AKIAIOSFODNN7EXAMPLE, can you review this?

🐦 sensitive-canary: prompt masking is not supported

  [mask-secret] cannot mask prompt content.
  The following sensitive data was detected:

  [Secret] AWS Access Key ID (aws-access-key): AKIA****MPLE

  Please choose one of the following:

  1. Manually redact the values above and resubmit
  2. To send as-is, add an allow tag to your prompt:
       [allow-secret]  — allow secrets
       [allow-all]     — bypass all sensitive-canary checks

Allow + Mask tag priority

When both [allow-*] and [mask-*] tags appear in the same prompt, the tag that appears first wins for each category (secret, pii). [allow-all] and [mask-all] resolve both categories at once.

Example	Result
`[allow-secret] [mask-secret] …`	secret allowed
`[mask-secret] [allow-secret] …`	masking not supported error
`[allow-secret] [mask-pii] …`	secret allowed, PII mask error

File structure

.claude-plugin/
  plugin.json                  plugin manifest
hooks/
  hooks.json                   Claude Code hook configuration
src/
  user-prompt-submit-hook.ts   UserPromptSubmit hook
  pre-tool-use-hook.ts         PreToolUse hook
  lib/
    inspector.ts               allow tag parsing, message scanning
    rules.ts                   secret and PII detection rule definitions

Development

npm install        # install dependencies

npm test           # run tests
npm run test:watch # run tests in watch mode
npm run typecheck  # type check (tsc)
npm run lint       # lint with Biome (no changes)
npm run fix        # lint + auto-fix with Biome
npm run ci         # typecheck + lint + tests (for CI)