Fetter IO

Fetter MCP

Fetter provides a remote Model Context Protocol (MCP) server at https://mcp.fetter.io/mcp that gives AI coding agents real-time access to Python package vulnerability data. Built on fetter, it queries PyPI and OSV to surface known CVEs, CVSS scores, and safe versions so your agent can make informed dependency decisions as it writes code.

To explore related functionality directly in the browser, visit Fetter IO Lookup.

For implementation details, issues, or feature requests, visit fetter-mcp.

Installation

The Fetter MCP server uses the HTTP transport and requires no local installation. Just register the remote URL with your MCP client.

claude mcp add --transport http fetter https://mcp.fetter.io/mcp

codex mcp add fetter --url https://mcp.fetter.io/mcp

https://mcp.fetter.io/mcp

Agent Usage

Once installed, the Fetter MCP tools are available to your AI agent during coding sessions. The agent can call them automatically when adding or auditing dependencies; no explicit tool invocation is required in your prompts.

How It Works

The agent selects the appropriate tool based on context:

• Adding a new package: most_recent_not_vulnerable to find a safe version
• Validating a specific pinned version: is_vulnerable for a definitive answer
• Auditing an existing specifier: lookup to see affected versions

Most Recent Not Vulnerable

The most_recent_not_vulnerable tool finds the most recent version of a package that has no known vulnerabilities. Provide only a package name and the server will search recent releases for a safe version. Useful when pinning a dependency to the latest clean release.

Example

Request

{
  "jsonrpc": "2.0",
  "method": "tools/call",
  "id": 2,
  "params": {
    "name": "most_recent_not_vulnerable",
    "arguments": {
      "name": "cryptography"
    }
  }
}

Response

{
  "jsonrpc": "2.0",
  "id": 2,
  "result": {
    "content": [],
    "structuredContent": {
      "package": "cryptography",
      "version": "46.0.5",
      "vulnerabilities": [],
      "vulnerable": false
    },
    "isError": false
  }
}

Find Vulnerabilities

The is_vulnerable tool checks if a specific package version has known vulnerabilities. Requires an exact version specifier. Returns vulnerability IDs, summaries, CVSS scores, severity ratings, and reference URLs.

Example

Request

{
  "jsonrpc": "2.0",
  "method": "tools/call",
  "id": 2,
  "params": {
    "name": "is_vulnerable",
    "arguments": {
      "name": "requests==2.19.1"
    }
  }
}

Response

{
  "jsonrpc": "2.0",
  "id": 2,
  "result": {
    "content": [],
    "structuredContent": {
      "package": "requests",
      "version": "2.19.1",
      "vulnerabilities": [
        {
          "cvss_score": 5.3,
          "id": "GHSA-9hjg-9r4m-mvj7",
          "severity": "(Medium):",
          "summary": "Requests vulnerable to .netrc credentials leak via malicious URLs",
          "url": "https://osv.dev/vulnerability/GHSA-9hjg-9r4m-mvj7"
        },
        {
          "cvss_score": 5.6,
          "id": "GHSA-9wx4-h78v-vm56",
          "severity": "(Medium):",
          "summary": "Requests Session object does not verify requests after making first request with verify=False",
          "url": "https://osv.dev/vulnerability/GHSA-9wx4-h78v-vm56"
        },
        {
          "cvss_score": 6.1,
          "id": "GHSA-j8r2-6x86-q33q",
          "severity": "(Medium):",
          "summary": "Unintended leak of Proxy-Authorization header in requests",
          "url": "https://osv.dev/vulnerability/GHSA-j8r2-6x86-q33q"
        },
        {
          "cvss_score": 7.5,
          "id": "GHSA-x84v-xcm2-53pg",
          "severity": "(High):",
          "summary": "Insufficiently Protected Credentials in Requests",
          "url": "https://osv.dev/vulnerability/GHSA-x84v-xcm2-53pg"
        },
        {
          "cvss_score": null,
          "id": "PYSEC-2018-28",
          "severity": null,
          "summary": "",
          "url": "https://osv.dev/vulnerability/PYSEC-2018-28"
        },
        {
          "cvss_score": null,
          "id": "PYSEC-2023-74",
          "severity": null,
          "summary": "",
          "url": "https://osv.dev/vulnerability/PYSEC-2023-74"
        }
      ],
      "vulnerable": true
    },
    "isError": false
  }
}

Search Packages

The lookup tool looks up a package by name and optional version specifier to find which versions are available and whether they have known vulnerabilities. Supports specifiers such as "requests", "numpy>=2.0", or "flask==3.0.0".

Example

Request

{
  "jsonrpc": "2.0",
  "method": "tools/call",
  "id": 2,
  "params": {
    "name": "lookup",
    "arguments": {
      "name": "requests>=2.32.0",
      "retain_passing": true
    }
  }
}

Response

{
  "jsonrpc": "2.0",
  "id": 2,
  "result": {
    "content": [],
    "structuredContent": {
      "package": "requests",
      "versions": [
        {
          "version": "2.32.0",
          "vulnerabilities": [
            {
              "cvss_score": 5.3,
              "id": "GHSA-9hjg-9r4m-mvj7",
              "severity": "(Medium):",
              "summary": "Requests vulnerable to .netrc credentials leak via malicious URLs",
              "url": "https://osv.dev/vulnerability/GHSA-9hjg-9r4m-mvj7"
            }
          ],
          "vulnerable": true
        },
        {
          "version": "2.32.1",
          "vulnerabilities": [
            {
              "cvss_score": 5.3,
              "id": "GHSA-9hjg-9r4m-mvj7",
              "severity": "(Medium):",
              "summary": "Requests vulnerable to .netrc credentials leak via malicious URLs",
              "url": "https://osv.dev/vulnerability/GHSA-9hjg-9r4m-mvj7"
            }
          ],
          "vulnerable": true
        },
        {
          "version": "2.32.2",
          "vulnerabilities": [
            {
              "cvss_score": 5.3,
              "id": "GHSA-9hjg-9r4m-mvj7",
              "severity": "(Medium):",
              "summary": "Requests vulnerable to .netrc credentials leak via malicious URLs",
              "url": "https://osv.dev/vulnerability/GHSA-9hjg-9r4m-mvj7"
            }
          ],
          "vulnerable": true
        },
        {
          "version": "2.32.3",
          "vulnerabilities": [
            {
              "cvss_score": 5.3,
              "id": "GHSA-9hjg-9r4m-mvj7",
              "severity": "(Medium):",
              "summary": "Requests vulnerable to .netrc credentials leak via malicious URLs",
              "url": "https://osv.dev/vulnerability/GHSA-9hjg-9r4m-mvj7"
            }
          ],
          "vulnerable": true
        },
        {
          "version": "2.32.4",
          "vulnerabilities": [],
          "vulnerable": false
        },
        {
          "version": "2.32.5",
          "vulnerabilities": [],
          "vulnerable": false
        }
      ]
    },
    "isError": false
  }
}