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

Goes well beyond the readOnly/openWorld annotations: discloses latency (~30 s, allow a 60 s timeout), payment model (x402 in USDC on Base/Solana/Arc, $0.0065 per successful call), that failed calls and no-speech 404s are not charged, and that oversized media is refused. For a paid, external-facing tool this is exactly the operational detail an agent needs before invoking.

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?

Front-loads purpose, then outputs, then pricing, then timing/payment — a sensible ordering with no filler sentences. The pricing clause is a dense run-on that partly duplicates the schema, which keeps it from a 5.

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?

Even though an output schema exists, the description still previews the return shape (text, timestamped segments, language, duration, optional speaker labels) and covers cost, latency, failure modes and payment. Nothing an agent needs to call this correctly or budget for it 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%, so the schema already documents url, language, speakers and maxMinutes, including the same per-minute pricing. The description adds only marginal semantics (maxMinutes sets the price tier and caps accepted length), so the baseline 3 applies.

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 ("Speech to text from a media link") and enumerates exactly which platforms/URL types are accepted, which lets an agent distinguish it from text-only siblings. It stops short of naming or contrasting the closest alternatives (transcribe, youtube_transcript), so it falls just short of 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?

The platform enumeration plus the "Longer media is refused unpaid" and "YouTube returns captions" lines give clear context for when this tool applies and what it will do. There are no explicit exclusions or routing statements pointing the agent to a sibling for a given case, so it is clear-context without alternatives.

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