ProjectDiscovery MCP Server

subfinder

Discover subdomains for a target domain using passive sources to identify potential attack surfaces during security reconnaissance.

Instructions

Discover subdomains for a given domain using passive sources

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "domain": "<domain>"
    },
    "name": "subfinder"
  }
}

Input Schema

Name	Required	Description	Default
`domain`	Yes	Target domain (e.g., example.com)
`silent`	No	Show only subdomains in output

Schema Changelog

Changes observed during successful MCP inspections.

First observedv1.0.0Mar 14, 2026

TDQS

C2.9/5.0

Behavior2/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

No annotations are provided, so the description carries the full burden of behavioral disclosure. It states the tool uses 'passive sources,' which implies non-intrusive discovery, but does not detail what this entails (e.g., rate limits, data sources, permissions required, or output format). For a tool with no annotations, this leaves significant gaps in understanding its behavior.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is a single, efficient sentence: 'Discover subdomains for a given domain using passive sources.' It is front-loaded with the core purpose, has zero wasted words, and is appropriately sized for the tool's complexity.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness2/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the lack of annotations and output schema, the description is incomplete. It does not explain what the tool returns (e.g., list of subdomains, errors) or behavioral aspects like rate limits or data sources. For a tool with no structured support, the description should provide more context to be fully helpful.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The input schema has 100% description coverage, with clear documentation for both parameters ('domain' and 'silent'). The description does not add any additional meaning beyond what the schema provides, such as explaining the implications of 'passive sources' on parameter usage. Since the schema does the heavy lifting, the baseline score of 3 is appropriate.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the tool's purpose: 'Discover subdomains for a given domain using passive sources.' It specifies the verb ('discover'), resource ('subdomains'), and method ('passive sources'), making the intent unambiguous. However, it does not explicitly differentiate from sibling tools like dnsx or nuclei, which may also involve domain-related operations, so it doesn't reach the highest score.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines2/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description provides no guidance on when to use this tool versus alternatives. It mentions 'passive sources' but does not specify contexts where this is preferred over active methods or other sibling tools. Without any when-to-use, when-not-to-use, or alternative recommendations, the agent lacks usage direction.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

Deploy Server