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

Beyond the annotations (which only say it is non-read-only, non-idempotent, non-destructive, open-world), the description discloses the billing prerequisite (positive balance), that the call itself is free, the 10-minute URL expiry, and the 20-per-minute-per-user throttling. Those are exactly the operational constraints an agent needs before retrying or looping.

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?

Three tight sentences, each carrying distinct information: capability and limits, cost/prerequisite and handoff, then expiry and rate limit. Nothing is redundant and the critical constraint is front-loaded.

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?

With no output schema, the description does supply the key return cues (a signed upload URL and a publicUrl to reuse), plus expiry and throttling. It leaves the exact response shape and failure behavior implicit, which keeps it from a perfect score for a two-parameter tool.

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%, with the enum and the maximum for contentLength already documented, so the baseline of 3 applies. The description reinforces the size cap and media categories but adds no new detail about how contentType or contentLength should be chosen.

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 precise verb and resource ('Get a signed URL to PUT one local image, video or audio file'), states the 25 MiB ceiling, and ties the result to the create_generation workflow via publicUrl, which clearly separates it from siblings like list_generations or estimate_cost.

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 states the context of use ('use publicUrl as a generation input') and the prerequisites (positive balance, file limits), plus the rate limit and expiry. It stops short of naming an alternative tool or saying explicitly when not to use it, so it lands just below the top mark.

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