iac-guard-mcp

IaC review_diff for agents: Checkov (optional) or builtin regex policies over Terraform/Bicep — structured findings JSON.

Who it's for: Cloud security + platform SAs embedding IaC review into agent workflows.

Why this exists

PR bots that only say "looks fine" are useless. iac-guard reviews fixtures (or diffs) for classic Azure foot-guns — open NSGs, public blobs — and returns findings plus a static explanation template agents can cite.

Related MCP server: pr-guard-mcp

Install

python -m venv .venv && source .venv/bin/activate
pip install -e .
# optional MCP SDK transport:
pip install -e ".[mcp]"
# optional Checkov:
pip install checkov

Or with pipx (once published to PyPI): pipx install iac-guard-mcp — until then use editable install from this repo.

30-second demo

python -m iac_guard --help
python -m iac_guard fixtures/bad_nsg.tf || true
python -m iac_guard fixtures/bad_nsg.bicep || true

Or simply:

make demo

What it is NOT

• Not a full OPA / Gatekeeper platform

• Not an auto-remediator that runs terraform apply

• Not a substitute for org policy + Defender for Cloud

Design & Engineering

I designed this so an agent reviewing infrastructure code can point at a specific policy finding instead of saying "looks fine".

Design goals

• Review Terraform and Bicep for classic Azure foot-guns (SSH open to the internet, public blob access).

• Return structured findings JSON plus a plain explanation that agents can cite.

• Work with no extra tools installed, and get better when Checkov is available.

• Expose the same review as an MCP tool for Cursor or any MCP host.

Architecture

flowchart LR
    F[.tf / .bicep file] --> D{Checkov installed<br/>and preferred?}
    D -- yes --> C[checkov_runner.py<br/>Checkov JSON -> findings]
    D -- no / fails --> B[policies.py<br/>builtin regex policies]
    C --> O[findings JSON<br/>policy_id, severity, description, source]
    B --> O
    O --> CLI[CLI: python -m iac_guard]
    O --> MCP[MCP tool: review_diff<br/>mcp_server.py, stdio]

Key design decisions and trade-offs

Engineering details

• Stack: Python 3.10+, optional mcp SDK extra (pip install -e ".[mcp]"), optional Checkov.

• Builtin policies: NSG-SSH-OPEN (port 22 from *) and STORAGE-PUBLIC-BLOB, for both Terraform and Bicep syntax.

• Fixtures: fixtures/bad_nsg.tf and fixtures/bad_nsg.bicep.

• CI: make demo checks findings are produced for both fixtures; workflow template in docs/ci/demo.yml.

What I'd do next

• More builtin Azure policies (private endpoints, TLS versions).

• A PR comment formatter.

• A multi-file diff MCP tool, so it can review a whole PR at once.

Roadmap

• More builtin Azure policies (private endpoints, TLS)

• PR comment formatter

• MCP tool for multi-file diffs

Contributing

See CONTRIBUTING.md. Be kind — CODE_OF_CONDUCT.md. Security reports: SECURITY.md.

MCP / Cursor plug-in

Install the optional MCP extra, then point Cursor (or any MCP host) at the stdio server:

pip install -e ".[mcp]"

Example ~/.cursor/mcp.json entry:

{
  "mcpServers": {
    "iac-guard-mcp": {
      "command": "python",
      "args": ["-m", "iac_guard.mcp_server"],
      "cwd": "/absolute/path/to/iac-guard-mcp"
    }
  }
}

Without the SDK, list tool schemas via CLI (tools subcommand where available) or see src/iac_guard/ for the JSON-RPC-shaped tool table.

License

Apache-2.0 (SPDX). Full text in LICENSE.