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Understand

dev.understand

Read-onlyIdempotent

Get cited answers for why a file, module, ticket, or commit exists via deterministic git-history evidence; no API key required.

Instructions

Cited answer for why a file, module, ticket, or commit exists. Deterministic; no API key required.

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": {
      "target": "<target>"
    },
    "name": "dev.understand"
  }
}

Input Schema

Name	Required	Description	Default
`target`	Yes	File path, module dir, ticket key (PROJ-123), or commit SHA
`private`	No	Lower visibility ceiling to private. Does not load personal prefs.

Output Schema

Name	Required	Description	Default
`claims`	Yes
`owners`	Yes
`outcome`	No
`subject`	Yes
`summary`	No
`degraded`	Yes
`visibility`	Yes
`schemaVersion`	Yes
`contractSources`	Yes
`contractVersion`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.1.1Sep 12, 2026

TDQS

A3.8/5.0

Behavior4/5

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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so safety is covered. The description adds genuinely new behavioral facts not in any structured field: the operation is deterministic and requires no API key, which matters for reproducibility and setup. It stops short of describing latency, scope limits, or what the citations look like.

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?

Two compact sentences with zero filler; the core promise (cited answer, target kinds) is front-loaded and the operational caveats (deterministic, no API key) follow. Every clause earns its place.

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

Completeness4/5

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

With a full input schema, an output schema, and annotations covering the safety profile, the description carries little remaining burden and discharges most of it via the determinism/no-API-key note. The only gap is the absence of explicit usage boundaries, minor for a simple read-only lookup tool.

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 description coverage is 100%, so both parameters are fully documented in the schema, including the multi-format 'target' (file path, module dir, ticket key, commit SHA) and the 'private' visibility switch. The description adds no additional parameter semantics, so the baseline 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 states a specific outcome — a 'cited answer' — and enumerates the target kinds it reasons about (file, module, ticket, commit), which is more concrete than the abstract name 'understand' suggests. It is clear what the tool produces, though the phrasing 'why ... exists' leaves the exact output shape to the output schema.

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?

Usage is implied by the purpose: reach for this when you need the rationale/provenance behind an artifact. There is no explicit when-to-use/when-not guidance, no prerequisites, and no siblings to route away from, so the guidance never rises above inference.

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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