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

Annotations only declare openWorld/write/non-destructive; the description adds real substance beyond that: "The picture is not changed" (scope of mutation), "keeping the video's own sound under it unless keep_original is false" (mixing behavior), "the finished video comes into the chat" (where output lands), and "Free" (cost). It does not cover failure cases or duration/mix limits.

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?

Three sentences, front-loaded with the primary single-sound path before the batch alternative, with no filler. The cues sentence is dense but the parenthetical example keeps it readable; "Free." is terse but informative.

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 7-parameter write tool with no output schema and non-destructive annotations, the description covers input sourcing, the two operating modes, original-audio behavior, output destination, and cost — everything an agent needs before calling it.

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; the description earns above that by clarifying the mutual exclusivity of cues versus sound_id/sound_url and by naming list_my_audio as the source of valid sound ids, which the schema itself does not cross-reference.

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?

"Lay one of your saved sounds ... or a sound in this chat onto your video at a given second" names a specific verb (lay/overlay), both sound sources, the target resource (video), and the placement mechanism. This is clearly distinct from siblings like generate_sound, extract_sound_effect, or stitch_videos.

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 routes between two modes: single sound via sound_id/sound_url, or "For many sounds ... pass cues instead." It also points to list_my_audio for obtaining sound ids. It stops short of naming a competing sibling tool for video audio work, so a 4 rather than a 5.

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