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mcp-nexus

mcp-nexus

by fyrlabs
OverviewSchemaSourceRelated ServersDiscussionsAdmin
TypeScript
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Describe capabilities

describe_capabilities

Retrieve full metadata and input schemas for capability IDs from search results. Use these schemas to discover required parameters and invoke capabilities correctly.

Instructions

Return the full metadata and input schemas for the given capability IDs.

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": {
      "capabilityIds": "<capabilityIds>"
    },
    "name": "describe_capabilities"
  }
}

Input Schema

NameRequiredDescriptionDefault
capabilityIdsYesCapability IDs returned by search_capabilities

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv0.10.0

TDQS

B3.4/5.0
Behavior3/5

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

No annotations are provided, so the description carries the burden. It clearly states the tool returns metadata and schemas, which is a read-like operation, but it doesn't disclose any limitations, such as whether invalid IDs cause errors or whether the returned data is verbose. The description is accurate but sparse on behavioral nuances.

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

Conciseness4/5

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

A single clear sentence that is entirely on-topic. It front-loads the action and object, with no filler. Could earn a 5 if it referenced a sibling or workflow, but it remains efficient.

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

Completeness3/5

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

Given there is no output schema and no annotations, the description is the sole source of behavioral information. It tells the agent what the tool returns, but for a metadata-inspection tool, an agent might need to know whether it can be used before executing a capability or how errors are surfaced. Still, for a simple lookup tool, this is adequate.

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?

Schema coverage is 100%, so the schema already documents the 'capabilityIds' parameter. The description adds the purpose context ('full metadata and input schemas') but doesn't add format or constraint details beyond the schema. Baseline 3 applies.

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?

States a specific verb ('Return') and resource ('metadata and input schemas') for given capability IDs. It distinguishes itself from sibling tools like search_capabilities (which likely finds capabilities) and execute_capability (which runs them), though it doesn't explicitly name them.

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

Usage Guidelines3/5

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

The description implies usage: given capability IDs, retrieve metadata. The parameter description notes IDs come from search_capabilities, implicitly showing a workflow step. However, it doesn't state when to use this vs execute_capability or search_servers, leaving some inference needed.

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

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