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

Annotations already cover the safety profile (readOnly, idempotent, openWorld, non-destructive), yet the description adds substantial operational context beyond them: the 15-minute limit, 20 MB base64 cap, automatic language detection, specific error codes (413 over-length, 422 not audio), and the $0.03 USDC x402 payment requirement. This is exactly the kind of cost/limit disclosure 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-loaded with capability and limits, then inputs, then return shape, then errors and price. Every clause carries operational information (formats, duration cap, cost) with 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?

Although no output schema exists, the description spells out the return shape ({language, duration, text, segments with start/end times}), documents both failure codes, and states the price. For a three-parameter, zero-required transcription tool, nothing needed 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 coverage is 100%, so the baseline is 3, but the description reinforces the url-or-base64 choice, flags language as an optional 2-letter code, and ties the format list and size constraints to what the parameters accept. It adds modest value over the schema rather than relying on it entirely.

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 (transcribe speech from an audio/video file), names the engine (Whisper), enumerates supported formats, and caps length at 15 minutes. An agent can immediately distinguish this from siblings like ocr_read_text or convert_file.

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?

"Use when you need the words from a voice note, meeting, podcast clip or video" gives clear positive context for when to reach for this tool. It stops short of naming alternatives or exclusions (e.g. when to prefer ocr_read_text for image-borne text), so it is clear but not fully routing.

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