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

Annotations declare readOnly/openWorld/non-destructive, and the description goes well beyond them: per-call price ($0.04 USDC), the x402 payment mechanism and supported chains, automatic payment for x402 MCP clients, voice licensing for commercial use, and return fields (audio_base64, duration). This is exactly the extra behavioral context an agent needs before invoking a paid tool.

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?

Purpose is front-loaded and the dense param list is scannable, but it restates enum values already in the schema and runs long as a single block. Every sentence is still informative, so the minor redundancy is tolerable.

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 supplies the return shape (audio_base64 and duration), the cost and payment path, and a runnable free-sample input. An agent has everything needed to call it correctly and anticipate the billing behavior.

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 0%, so the description must carry parameter meaning, and it does: it documents text (required, max 2000 characters — a constraint absent from the schema), voice default, language options, speed range/default, and format default. All five parameters are covered with values the schema alone does not convey.

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 ('Convert text to natural speech audio') with formats and the underlying engine (neural Piper voices), and names the available voices. It is immediately distinguishable from the reverse-direction sibling audio_transcribe.

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 implied by the purpose and the pricing/sample detail, but the description never states when to choose this over alternatives or when-not to use it (e.g., vs audio_transcribe for the inverse task). Adequate but no explicit routing guidance.

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