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

Annotations already declare readOnlyHint=true and destructiveHint=false, and the description reinforces this ('Reads or computes only and changes nothing'). It adds billing behavior beyond the annotations — per-call charge, first 25 free, failed calls free, repeats not free — which usefully explains why idempotentHint=false.

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?

Front-loads the core behavior and example before the pricing block. The pricing/payment sentence is longer than the functional content, but it is the only padding.

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?

No output schema exists, so the description carries the return-value burden — it does, naming both the MIME type and the inline-display flag. Input format is covered by example. Only minor gaps such as fallback behavior for unknown extensions remain.

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 coverage is 100% and the single parameter is already documented, so the baseline is 3. The description earns an extra point by showing through examples that either a full file name or a bare extension is acceptable input.

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?

States a specific verb and resource: resolves the MIME content type for a file name or extension, and additionally reports whether browsers display it inline. The example mapping 'report.pdf → application/pdf' removes any ambiguity, and no sibling tool overlaps with this function.

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?

Gives a concrete usage context ('when uploading or serving files') and a call example. It doesn't name alternatives or exclusions, but for a lookup tool with no near-siblings there is little to disambiguate.

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