opsecforge-mcp

A local MCP server (stdio) for AI coding agents such as Claude Code, Codex and Cursor. It helps keep secrets out of the model context: the agent passes a file path or an environment variable name, the work happens on your machine, and only redacted or derived results come back.

• Nothing is sent to any remote service. The server makes no network requests.
• No account, no API key, no telemetry.
• Source: github.com/cyberdroid2077/opsecforge-tools (MIT). It reuses the same tested code that powers the browser tools at opsecforge.com.

Read the limitations below before relying on this. Redaction is heuristic, the Claude Code hook is a best-effort guard rather than a sandbox, and Codex and Cursor have no hook at all.

Install

Requires Node.js 20 or newer.

Claude Code: plugin (recommended: MCP server + guard hook + skill)

/plugin marketplace add cyberdroid2077/opsecforge-tools
/plugin install opsecforge@opsecforge

The plugin adds three things:

1. the MCP server (npx -y [email protected]), exposed as mcp__plugin_opsecforge_opsecforge__*;
2. a PreToolUse hook that blocks Read, Grep and Bash calls that would directly read .env, *.pem, *.key, id_rsa*, id_ed25519*, credentials, *.p12 and similar files, and tells the model to use redact_file instead (.env.example, .env.sample, .env.template and *.pub are allowed);
3. a skill that tells the agent which tool to use when.

The hook's onFailure: "block" setting needs a recent Claude Code (v2.1.295 or later according to the hooks documentation). On older versions a hook that times out may be skipped instead of blocking.

Claude Code: MCP server only

claude mcp add opsecforge -- npx -y opsecforge-mcp

Codex

Add to ~/.codex/config.toml:

[mcp_servers.opsecforge]
command = "npx"
args = ["-y", "opsecforge-mcp"]

(or codex mcp add opsecforge -- npx -y opsecforge-mcp).

Cursor

Add to .cursor/mcp.json (project) or ~/.cursor/mcp.json (global):

{
  "mcpServers": {
    "opsecforge": {
      "type": "stdio",
      "command": "npx",
      "args": ["-y", "opsecforge-mcp"]
    }
  }
}

Environment variables the tools read

verify_webhook and inspect_jwt read secrets from environment variables by name. The variable must exist in the environment of the MCP server process. Export it in the shell that starts the agent, or add an env entry to the server's configuration in your client. Do not paste the secret into chat and do not commit it.

Optional hardening: set OPSECFORGE_MCP_ROOTS to a path-delimiter-separated list of directories (for example /home/me/projects) and the file tools refuse paths outside them.

Tools

Every tool is read-only, runs locally, and returns readable errors instead of crashing the server.

redact_file({ path })

Reads a local text file and returns it with secrets replaced by [REDACTED], plus a findings summary: type, count and line numbers (of the original file). Original values are never returned, and no part of a value is shown. The response starts with a notice that the original values did not leave the machine or reach the model.

Only regular files (no directories, pipes, devices), at most 1 MiB; larger files fail with an explicit message. Binary files are refused. Detects, among others: private key blocks (including unterminated ones, which are masked from BEGIN to the end of the text), sensitive named fields (password, token, secret, *_KEY, ...), Authorization / cookie / API-key headers, URL credentials, AWS, Stripe, GitHub, GitLab, Slack, Google, OpenAI, Anthropic and SendGrid key formats, and JWT-shaped strings.

scan_secrets({ paths?, staged? })

Pre-commit check. Scans files or directories (paths) and/or only the lines added in git diff --cached (staged: true). Lists file:line, the secret type and a masked preview: the first 4 characters for values of 20 or more characters, otherwise just …. Never returns an original value. Directory scans skip .git, node_modules, build output and symlinks, read at most 2000 files of at most 1 MiB, and skip binaries.

redact_text({ text })

Redacts text the agent already has, for example before pasting logs into an issue or ticket. That text is already in the model context; this tool cannot take it back out. It only produces a safer copy to share outward. To keep a secret out of the context in the first place, use redact_file with a path.

verify_webhook({ provider, body_path, secret_env, signature, algorithm?, tolerance_seconds? })

Verifies a github (X-Hub-Signature-256), stripe (Stripe-Signature) or generic HMAC (hex or base64, sha1/sha256/sha512) signature offline.

• The secret comes only from the environment variable named by secret_env. There is no plaintext secret parameter; any unknown parameter (for example secret) is rejected with an explanation, and the value is not echoed.
• The body is read from body_path as raw bytes (up to 10 MiB). Save it exactly as received.
• Returns match / no match plus diagnostics: signature header well-formed or not; Stripe timestamp age and whether it is outside the tolerance (default 300 s); whether the body looks reformatted (it tests whether the signature would match with the trailing newline removed or added, CRLF/LF changed, a BOM removed, or the JSON minified or pretty-printed); whitespace or quote characters around the secret; a Stripe API key used where a whsec_ signing secret is needed.
• It never returns the secret or a computed signature.

inspect_jwt({ token_env?, token? })

Decodes a JWT and returns the header, the claims, time-claim status (exp, nbf, iat, auth_time) and risk notes: alg: none, HMAC algorithms that cannot be verified offline, a missing exp, jku/jwk/x5u headers. Decoding is not verification: the tool has no key and never checks the signature. Prefer token_env (the variable name) so the raw token does not pass through the model; a token parameter is already in the context. Claim values under secret-looking field names are masked, but the claims you get back are in the context either way.

file_checksum({ path, algorithm, expected? })

SHA-256 or SHA-512 of a local file (up to 32 MiB), optionally compared with an expected value (<hex>, sha256:<hex> and sha256sum output are accepted). A match proves only that the file equals whatever the expected value came from.

Honest limitations

• The hook is a best-effort guard, not a sandbox. It parses the text of tool calls. It does not stop a script from reading a secret file indirectly (python app.py that opens .env, make, docker compose config), grep -r over a directory that contains a .env, commands that use shell variables or command output as file names (cat "$FILE", find . -name .env | xargs cat), or anything a language runtime does inside a program. Treat it as a speed bump that catches the common, accidental case.

• For stronger protection, combine it with Claude Code's own controls: run in its sandbox, and add Read deny rules for your secret paths in settings.json (check the permissions documentation for the exact pattern syntax), for example:

  { "permissions": { "deny": ["Read(./.env)", "Read(./.env.local)", "Read(**/*.pem)", "Read(~/.ssh/**)"] } }
  

  Deny rules also have gaps and can produce prompts or false positives; test them.

• Redaction is heuristic and can miss secrets. It recognises common formats and secret-looking field names. It does not know your custom token formats, secrets inside prose, base64-wrapped values, or secrets split across lines in unusual ways. Review the output before sharing it, and treat a clean result as "nothing matched", not "nothing there". It can also redact harmless values (false positives).

• Parameters and results of every MCP tool pass through the model. That is why the tools take paths and variable names. redact_text and inspect_jwt with token cannot keep what you hand them out of the context.

• Codex and Cursor have no equivalent of the Claude Code PreToolUse hook. There the tools are advisory: they only help if the agent chooses to call them instead of reading a file directly. Use each client's own permission and sandbox settings alongside them.

• Redacted output still contains everything that was not matched (hostnames, usernames, internal URLs, personal data).

• scan_secrets is not a replacement for a dedicated scanner with a maintained rule set in CI.

• If a secret has already reached a model context, a log or a commit, rotate it.

Learn more

Browser-local versions of these checks and the background behind them, all at opsecforge.com:

• Env file sanitizer and How to sanitize .env files before sharing
• Webhook debugger and Webhook signature validation with HMAC-SHA256
• JWT decoder and How to decode JWTs client-side
• Hash and file checksum generator and Hash generators and data integrity
• Environment variable security and secrets management
• AI agent credential security

License

MIT