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

With no annotations, the description carries the full burden. It discloses that the tool says whether the image is accepted and, if not, which error an upload would return, and it implies that the check itself does not consume quota. While it does not explicitly state whether the tool is read-only or quota-free, the phrasing 'instead of spending quota' provides enough behavioral context.

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 sentences: the first states the function, the second gives a clear use case. Every word earns its place, and it is front-loaded with the core purpose.

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?

The tool has an output schema, so the return structure is covered. The description provides purpose, usage guidance, and behavioral context, which is sufficient given the simple optional parameters and no need to reference siblings.

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%, so the baseline is 3. The description mentions the three parameters (filename, MIME type, size) but adds no extra meaning beyond what the schema already provides; precedence of contentType over filename is already documented in the 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 states that the tool checks whether PiPic will accept an image based on filename, MIME type, and/or size, and reports the corresponding upload error if rejected. This specific verb and resource distinguish it from the sibling tools, which focus on compression facts and integration guides rather than acceptance validation.

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?

It explicitly advises using the tool to filter a file list locally instead of spending quota on requests that will be rejected. This gives clear when-to-use guidance and an implied alternative (making unnecessary uploads), which is exactly the kind of contextual direction an agent needs.

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