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

With no annotations, the description carries the full burden of behavioral disclosure. It mentions a key constraint: 'Hard cap of 500 lines per call.' It also clarifies the tool returns 'raw file excerpt,' implying it does no semantic interpretation. However, it doesn't explicitly state whether the operation is read-only (though 'Read' implies it) or what happens when the cap is exceeded. This is a minor gap.

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

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

The description is exceptionally concise: three short sentences, each earning its place. It front-loads the core purpose in the first sentence, provides usage direction in the second, and adds a critical constraint in the third. There is zero redundancy.

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

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

Given the tool's moderate complexity, no output schema, and no annotations, the description covers the essential context: purpose, when to use, and a hard constraint. The schema handles parameter details comprehensively. The only minor gap is that the return value format is not explicitly described, but 'Read a raw file excerpt' clearly implies the content returned. Overall, this is well-rounded for a focused read tool.

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

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

Schema description coverage is 100%, and the schema already thoroughly documents all four parameters (project, file_path, from_line, to_line), including defaults and the 500-line cap. The description provides no additional parameter-level semantics beyond what the schema already contains. Baseline 3 applies because the schema does the heavy lifting.

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

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

The description clearly states the action ('Read a raw file excerpt'), the resource ('from an indexed project'), and the scoping method ('by line range'). It also distinguishes itself from siblings by mentioning xmp4_search, xmp4_outline, and xmp4_source explicitly, making it clear that this is the tool for reading raw line ranges, not for searching or outlining.

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

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

The description gives explicit usage context: 'Use after xmp4_search/xmp4_outline locates the region of interest, or to expand a truncated xmp4_source snippet.' This tells the agent exactly when to use this tool versus the named alternatives. It effectively conveys the intended workflow.

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