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 only says 'Look up,' which implies a read operation, but it does not explain expected output, behavior for unknown extensions, case sensitivity, dot-prefixing, or the role of the q parameter. This is too thin for an agent to predict the tool's actual behavior.

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 a single concise sentence with no filler or redundant details, which is appropriate for a simple lookup tool. It loses a point because the leading 'Mime:' prefix is unnecessary and the structure provides only the bare minimum rather than any useful breakdown.

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 tool with two parameters, no annotations, and no output schema, this description is incomplete for confident invocation. It does not clarify whether q, ext, or both should be provided, nor what the return value looks like. The large sibling list of similar MIME-related tools also makes the missing differentiation more costly.

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 schema descriptions are generic ('Q to process' and 'Ext to process'), so the tool description adds some meaning by clarifying that the lookup is by extension. The ext parameter becomes reasonably interpretable, but q remains unexplained. Since schema description coverage is 100%, the baseline is 3, and the description provides marginal value without fully resolving parameter 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 states a specific action ('Look up') and a specific resource ('MIME types'), and adds a scoping detail ('by extension'). It is not a tautology and an agent can understand the basic purpose. However, it does not explicitly differentiate itself from sibling tools like x402-mime-type or x402-mime-detect, so it falls short of a 5.

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 phrase 'by extension' implies when the tool is appropriate, but the description provides no explicit guidance about when to use this tool versus related siblings such as x402-mime-type, x402-mime-detect, or x402-content-type. There are no exclusion criteria or alternative routing hints, so usage remains merely implicit.

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