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

Annotations already declare readOnlyHint=true, destructiveHint=false, and idempotentHint=false; the description reinforces this with 'reads or computes only and changes nothing.' It adds genuinely non-structured context: per-call pricing ($0.002 x402 USDC / card key), 25 free calls, failed calls free, and the warning that repeats are charged—consistent with 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?

The core purpose is front-loaded, but billing details ($0.002/call, free tier, failed calls free) are interleaved into the same narrative as functional behavior, making the sentence dense and slightly noisy for a trivial lookup tool. Every clause is relevant, but the mixture of semantics and commerce could be better separated.

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?

There is no output schema, and the description compensates by describing both return dimensions (content type and inline-display flag). For a one-parameter lookup tool this is nearly sufficient; the only minor gap is not stating how unknown extensions are handled.

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% for the single required 'file' parameter, so baseline is 3. The description goes slightly beyond by demonstrating accepted input form ('Example: file=report.xlsx') and describing the second output dimension (inline display), which helps the agent understand what the input is used for.

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 ('MIME (content) type for a file name or extension') and anchors it with a concrete example ('report.pdf → application/pdf'). This clearly separates it from siblings like base64_encode or hash, which also operate on files/strings but return different artifacts.

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?

'Use when uploading or serving files' gives a concrete usage context, and the inline-display note signals the serving use case. No explicit exclusions or named alternatives, but no sibling in the list plausibly overlaps (nothing else resolves MIME types), so the lack of routing guidance is low-risk.

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