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

Annotations mark this as a non-read-only, non-idempotent mutation but say nothing else. The description adds the operational contract the agent actually needs: the URL is PUT-only, single-object, and expires in one hour, the raw bytes must be uploaded before captioning, and retries are only safe when reusing the idempotencyKey. This is consistent with idempotentHint=false rather than contradicting it.

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?

Four dense sentences, front-loaded with the eligibility constraint and the return value, then the PUT workflow, then the idempotency caveat. No filler and nothing repeated from the schema verbatim.

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?

An output schema exists, yet the description still tells the agent what the call yields (a one-hour PUT URL and a jobId) and what to do with it, covering the full call sequence for a zero-required-param tool. Nothing needed to invoke it correctly is missing.

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, but the description adds decision guidance beyond the schema: pass contentLength only when the size is known because the URL becomes size-bound, otherwise omit it. It does not mention sha256, though the schema fully documents that parameter, so no information is actually lost.

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?

States a specific verb and resource: it returns a PUT-only upload URL for a single object, restricted to a caller-side video file of at most 2 GB. It also cleanly separates itself from caption_video, which is named as the follow-up/alternative tool, so an agent can pick it without opening any schema.

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?

Usage is fully bounded: use it only for a local video file, skip it entirely and pass inputUrl to caption_video when the video already sits at an https URL, and call caption_video with the returned jobId after the PUT. Retry conditions are also spelled out (same idempotencyKey or a new upload is created).

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