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.

Tools:

most_recent_not_vulnerable: find the latest release of a package that is free of known vulnerabilities
is_vulnerable: check whether a specific pinned version has known CVEs
lookup: find available versions and their vulnerabilities for any package or specifier

Installation

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

Claude Code

Terminal

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

Codex

bash

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

Other MCP Clients

For any other MCP-compatible client, provide the following remote server URL using the HTTP transport:

Code

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.

Example prompts

"Add the latest safe version of requests to requirements.txt"
"Are there any known vulnerabilities in my current dependencies?"
"What is the most recent version of pillow with no CVEs?"
"Before pinning cryptography, check whether 42.0.5 is vulnerable"

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`

Find 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.

Parameters

package_name — package name only (no version specifier), e.g. "requests"

Example Request

config.json

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

Example Response:

config.json

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

`is_vulnerable`

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

Parameters

dep_spec — exact version specifier, e.g. "requests==2.31.0"

Example Request

config.json

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

Example Response:

config.json

{
  "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
  }
}

`lookup`

Look 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".

Parameters

dep_specs — package name or version specifier
cvss_threshold — filter to vulnerabilities at or above this CVSS score (0–10)
max_observed_score — return only the highest CVSS score per version rather than all individual vulnerabilities
count — limit the number of recent versions checked
retain_passing — include versions with no known vulnerabilities in the results

Example Request

config.json

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

Example Response:

config.json

{
  "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
  }
}