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

With no annotations, the description carries the behavioral burden and does real work: it discloses a hard quota (10 updates per film), expected latency (a few minutes to render), a plan restriction (music is Premium and Ultimate), and that previously kept remakes are preserved in the re-render. It stops short of saying whether prior captions/music are replaced or whether an update is consumed on failure — material for a mutation with a finite quota.

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?

The action and its scope land in the first clause, followed by the UI anchor, then parameter clarifications, then plan/quota/latency constraints. Dense but every clause carries information an agent needs; nothing is padding.

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 6-parameter, zero-required mutation with no output schema and no annotations, the description supplies the missing context that matters: preconditions, plan gating, quota, and render time. It is nearly sufficient, though it omits what state is reset in the re-render (existing captions/music) and any hint about what the call returns (likely a job id for check_video).

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 already 83%, and most of the description's parameter text restates it ('music = one track or mood' mirrors 'A track name or mood from list_music'; music_tracks restates the schema's ordering note). It does hint at the one-track vs multi-track distinction and music_auto's adaptive behavior, but leaves genuine gaps: whether music/music_tracks/music_auto are mutually exclusive, and music_volume has no description anywhere.

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 ('Re-render a finished 3D film') and scopes it to a known UI affordance ('Update video' under 'Finish your film'), so the agent can distinguish it from create_3d_film or fix_3d_shot without opening a schema. It also names what the update carries forward (kept remakes) and what it can add (captions, music).

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?

The phrase 'finished 3D film' plus the UI affordance establishes the precondition clearly, and it flags the Premium/Ultimate plan gate plus the 10-updates-per-film cap so the agent knows when this call is even permitted. It never names an alternative for the adjacent use case (e.g. editing an unfinished film via fix_3d_shot/keep_3d_shot), which keeps it out 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.