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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so the safety profile is covered. The description goes well beyond that by disclosing the cost model ('one perception per started minute of audio'), the free-key monthly minute allowance, and the input size cap — non-obvious operational facts an agent needs before spending quota. It also states the return shape, which the definition otherwise lacks since there is no output schema.

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 sentences, no filler, with the core action and size limit front-loaded before the output and cost details. The colon-separated list of return fields is efficient. Nothing here is wasted, though the closing sentence about free keys could be compressed slightly.

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 one-parameter tool with no output schema, the description covers action, input constraint, return contents, and cost/quota — enough to call it correctly and predict the bill. It does not address failure modes (unreachable URL, oversized file, long-running async behavior), which is the only material gap.

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?

With a single parameter at 100% schema description coverage, the schema already defines 'target' as an http(s) URL of an audio or video file. The description adds only the 20 MB constraint, not URL format, accepted codecs, or timeout behavior. Baseline 3 is appropriate when the schema carries the load.

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 opens with a specific verb and resource: 'Transcribe speech from an audio or video URL'. It names concrete output artifacts (full text, language, timed segments), so the agent knows precisely what it gets back. It never explicitly routes against siblings like see or read, which is the only thing keeping it from a 5.

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 clear by implication: call this with an audio or video URL. The 20 MB ceiling is a practical gating condition the agent can check before calling. There is no explicit when-not-to-use statement or named alternative (e.g., 'for still images use see'), so it stops short of full guidance.

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