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

With no annotations, the description fully carries the behavioral burden and does so impressively: it discloses that conversion happens locally, the only network communication is when a video-site URL is passed, overwriting requires explicit opt-in, and unsupported requests return a format list. It also clarifies that max only shrinks and same-format output means size reduction, which prevents agent misexpectations.

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 information-dense and front-loaded with the core purpose and local-processing guarantee. It is written as one long paragraph, and the garbled '0通り・入力0形式' phrase is a readability defect, but every substantive sentence earns its place and no content is redundant.

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 highly polymorphic tool with 7 parameters and no output schema, the description covers formats, operations, constraints, network behavior, overwrite safety, and error-response behavior. Nothing critical for invoking the tool correctly is missing; it even handles edge cases like same-format compression and unsupported requests.

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%, but the description adds meaning beyond every parameter: input can be a URL or multiple files for PDF merge; to can be the same format to compress; max is shrink-only; columns has a default of stacking vertically; pages defaults to all pages; overwrite defaults to false to avoid silent deletion. This is excellent value-add over the raw JSON schema.

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 names the resource ('file') and the action ('convert to another format'), and it enumerates supported categories (image, video, audio, document, PDF, etc.). However, the opening parenthetical '0通り・入力0形式' is nonsensical and slightly undermines clarity, and the broad scope means it cannot be sharply distinguished from some conceivable conversion sibling.

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 concrete usage guidance for several scenarios: PDF merging requires multiple inputs, pages extracts ranges, columns controls the grid, max shrinks only, and same-format to compresses. It also says unsupported combinations return a list of possible formats. There are no sibling tools to compare against, so it cannot give explicit when-not-to-use alternatives, which keeps it just below 5.

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