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

Annotations already declare readOnlyHint=true and openWorldHint=false, and the description adds a genuinely useful trait beyond them: the check is performed locally 'without sending the file', so the agent knows no upload or external call occurs. It does not say what verdict/format comes back, which is left implied.

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?

Two tight sentences with the core action front-loaded and the usage condition second; every clause earns its place and nothing is repeated from the schema or annotations.

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 no output schema and no annotations about results, the description should at least indicate the shape of the answer (compliant/non-compliant, offending rule). It covers inputs well but leaves the return value entirely unstated.

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 description coverage is 60% (width and height have none), so the description meaningfully maps its concepts to parameters: 'size in bytes' -> file_size_bytes, 'pixels' -> width/height, 'type' -> format. It adds this conceptual mapping but no format or unit guidance, so it neither fully compensates nor is redundant.

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 gives a specific verb and resource: check a file's size/pixels/type against a website's upload rules, plus the key qualifier 'without sending the file'. It is clearly distinct from plain rule-fetchers like get_photo_requirements, though it does not explicitly contrast itself with the closer sibling interpret_upload_rules.

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 you already know the numbers (e.g. from the file's properties)' is an explicit precondition that tells the agent exactly when this tool applies. It stops short of naming the alternative to use when the numbers are unknown, so it is clear context rather than full when/when-not routing.

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