Estimate the cost of transcribing something

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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered. The description adds real value beyond that: it explicitly states nothing is transcribed or charged, and enumerates the returned fields (media length, price in minutes, balance coverage, queue-aware ETA), which is meaningful behavioral context for an agent deciding whether to call 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?

Two tight sentences: the first front-loads the value proposition and non-charging guarantee, the second gives the call condition and the return summary. No filler or repetition.

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 carries the burden of describing return values and does so concretely (length, price, balance coverage, ETA), and the usage condition is unambiguous. Nothing an agent needs to call 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 description coverage is 100% and the schema fully documents url, model (with per-model cost/speed tradeoffs) and features. The description adds no parameter-level detail of its own, so the baseline 3 is appropriate – the schema does the heavy lifting.

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+resource (estimate what a recording would cost and how long it would take) plus an explicit negative scope ('without transcribing it or charging anything'). This clearly distinguishes it from the transcribe sibling without needing to open either 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?

Gives an explicit trigger: 'Call this first whenever the recording might be long, or the user has not already agreed to spend.' That is a concrete when-to-use condition, and the 'without charging' framing implicitly names the alternative (transcribe) and why an agent would pick this one instead.

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