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

Beyond the readOnly/idempotent annotations, it discloses two non-obvious behaviors: the URL is private and expires in five minutes. The instruction not to publish the URL is a useful confidentiality constraint. It omits what happens on an expired or invalid id.

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 compact sentences with the core behavior front-loaded and the follow-up action second; no filler.

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 correctly covers the return value (a time-limited private URL) and caller obligations. However, for a single-parameter tool with zero schema documentation, leaving the meaning and source of 'id' unspecified is a material gap on the critical path to a correct call.

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?

There is one required parameter with 0% schema description coverage, and the description never explains what 'id' is or where it comes from (presumably an fp_ file id from generate_image or get_image_job). The phrase 'the user's requested local path' refers to a separate step, not to schema parameters, so it doesn't compensate.

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 concrete verb and resource ('Get a private download URL') and resolves the name/behavior mismatch by explaining that the tool returns a link rather than bytes. It stops short of differentiating itself from siblings like get_image_job, which may also surface URLs.

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 next step explicitly ('Download bytes to the user's requested local path using your file tools') and an exclusion ('do not publish the URL'), which is real operational guidance. It doesn't say when to prefer this over get_image_job or how to obtain the id first.

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