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

Adds substantial context beyond the annotations: consumes credits, dryRun is free and sends nothing, the output lands in a pending item that gets filled, and `auto` relies on cached transcripts and title accents. It also discloses the section-timing constraints (first at 0, ≥5 s apart, last ≥5 s before the end) that govern valid input — none of which the annotations convey.

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 the core action and effect, then handles sections, auto, dryRun, and cost in short ordered sentences. It is dense with backticked parameter names and constraint clauses, but essentially nothing is padding; a slightly lighter touch on the constraint list would be the only trim.

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?

For a 9-parameter, credit-consuming generation tool with no output schema, the description covers cost, mode exclusivity, section constraints, defaults, and what dryRun returns. What's missing is what happens after generation (async job? must poll generation_status/job_status?) and failure behavior, which an agent would need to complete the workflow.

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 baseline is 3, but the description goes further by clarifying that `sections` start times are measured in seconds into the generated track rather than timeline time — a genuinely confusing distinction the schema alone leaves ambiguous — and by spelling out spacing rules the schema doesn't encode.

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 ("Compose instrumental music with Sonilo") plus the concrete effect: a pending audio item is filled with the finished track on a "Music" track. That separates it cleanly from siblings like generate_sfx, generate_voice, and search_music, which an agent can rule out 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?

Explicitly frames the two operating modes and their exclusivity ("auto builds them from the timeline instead" vs `sections`), and explains when to use dryRun (free preview, no generation) versus the paid real call. It doesn't name a sibling alternative for the same job, but the mode-selection guidance is clear.

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