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

Annotations already declare readOnly/openWorld/non-destructive, and the description adds substantial non-obvious behavior: audio is deleted after the call, 10-minute and 24 MB limits, default model choice, $0.01 USDC pricing paid in-call via x402 on four chains, and automatic payment by x402 MCP clients. This is exactly the extra operational context annotations cannot carry.

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 the core purpose and then built as tight factual sentences covering cost, limits, formats and return shape. It is dense and slightly long, with the pricing/sample sentences leaning promotional, but every sentence carries usable information.

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?

There is no output schema, and the description compensates by naming the return fields (text, detected language, duration, segments with start/end seconds). Combined with formats, size/time limits, default model behavior and the payment flow, an agent has everything needed to invoke it correctly.

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 real value beyond it: it enumerates the accepted container formats (mp3, mp4, m4a, wav, ogg, webm, flac) and clarifies the otherwise-unstated mutual exclusivity rule 'Send audio_url or audio_base64' — important because the schema marks zero required parameters.

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 ('transcribe a voice note, meeting, podcast or call recording into text') plus concrete scope details (timestamps, ~100 languages, Whisper). It is immediately distinguishable from siblings like tts (opposite direction), ocr (image text) and language_detect (detection only) 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?

Gives clear when-to-use context (voice notes, meetings, podcasts, call recordings), the input alternatives (audio_url vs audio_base64, or the OpenAI-compatible HTTP endpoint), and even a runnable free-sample invocation. It never names a sibling tool or states when NOT to use this one, so it stops short of the top band.

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