I published my first GitHub Marketplace Action: Aster Guard MCP

I just published my first GitHub Marketplace Action: Aster Guard MCP.

Marketplace:
https://github.com/marketplace/actions/aster-guard-mcp

Repository:
https://github.com/Aster-Works/aster-guard

It is a lightweight, local-first security scanner for MCP and Claude Code configuration files.

The goal is intentionally small:

Before connecting an MCP server to your AI coding environment, check whether the configuration looks safe enough to trust.

Why I built it

MCP is becoming a very practical way to connect AI coding tools to real developer systems.

Depending on the MCP server, an AI agent may gain access to:

local files
shell commands
browsers
databases
SaaS APIs
internal developer tools

That is powerful. It is also a meaningful security boundary.

For example, a single .mcp.json entry can define a command to run, expose environment variables, grant filesystem access, or connect to a remote endpoint. Tool descriptions can also contain hidden instructions that shape how an agent behaves.

So I wanted a small check that runs before that connection happens.

What Aster Guard MCP does

Aster Guard statically scans MCP and Claude Code configuration files.

The important part is what it does not do:

it does not start the MCP servers it scans
it does not execute scanned commands
it does not send telemetry
it does not call external APIs during normal scans
it redacts secrets in output

It looks for risk patterns such as:

hidden agent instructions in tool descriptions
hardcoded secrets
sensitive file paths such as .ssh, cloud credentials, and .env
shell execution and dangerous install commands
destructive commands
overbroad filesystem access
unknown remote MCP endpoints
tool-name shadowing
obfuscated command patterns

The output includes a risk score, a grade, findings, and recommended next steps in English and Japanese.

Try it locally

You can run it without installing anything globally:

npx -y @asterworks/aster-guard scan

Or scan a specific config file:

npx -y @asterworks/aster-guard scan .mcp.json

Use it in GitHub Actions

Now that it is on GitHub Marketplace, you can add it to a workflow:

- uses: Aster-Works/aster-guard@v0.3.2
  with:
    path: .
    fail-on: high

You can also produce SARIF and upload the result to GitHub code scanning:

- uses: Aster-Works/aster-guard@v0.3.2
  with:
    path: .
    fail-on: high
    sarif: results.sarif

- uses: github/codeql-action/upload-sarif@v3
  if: always()
  with:
    sarif_file: results.sarif

Where it fits

Aster Guard is not trying to be a full security platform.

It is not a runtime firewall, antivirus tool, SIEM, or complete supply-chain scanner. It is a narrow pre-connection check for MCP configuration risk.

That narrow scope is deliberate. I wanted something that individual developers and small teams can run quickly before trusting an unfamiliar MCP server.

What I would love feedback on

This is still early, so the most useful feedback is practical:

Are the findings easy to understand?
Does the report help you decide what to do next?
Are there common MCP configuration risks it should detect?
Would this be useful in CI, or mainly as a local pre-check?

If you are experimenting with MCP or Claude Code, I would love for you to try it on a real configuration and open an issue with anything confusing, noisy, or missing.

Links: