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

With no annotations provided, the description must carry the full burden of behavioral disclosure. It explains the conditional behavior ('if it has one') and the return type ('MCP image content'), but it does not explicitly state that it has no side effects, nor does it mention error behaviors or access requirements.

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 two concise sentences that front-load the core purpose, condition, return type, and common use case. There is no redundant or filler wording.

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?

For a simple one-parameter read tool, the description covers what it does, the conditional nature of the result, what it returns, and why it's useful. It does not describe error behavior, but the low complexity and the 'if it has one' phrasing mitigate that gap.

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?

The only parameter 'id' is defined in the schema as a uuid but has no description, and the description does not mention it at all. With schema description coverage at 0%, the description should compensate and explain that 'id' refers to the file's identifier, but it does not, leaving room for ambiguity.

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 uses a specific verb 'Get' and explicitly names the resource 'JPEG thumbnail of a file', making it clear this tool is for previewing a file's thumbnail rather than the full file. This distinguishes it from siblings like get_file, read_file, and read_file_text.

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 explicitly states its practical use case: 'Useful for previewing images/videos without downloading the full file.' This tells an agent when to invoke it over file-download siblings, though it does not mention when not to use it or list alternative tools.

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