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

Annotations declare readOnlyHint=true and idempotentHint=true, so the description's job is to explain what the transform actually does and whether anything is persisted. Instead, 'Substitute all source copy' reads like a mutation of the stored scene, and the text never says whether the adapted scene is returned-only or saved; the caveat about extrapolation is too cryptic to resolve that, so real ambiguity remains despite the annotations.

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?

Two sentences with the action front-loaded, so it is reasonably tight. However, the second sentence is an unexplained warning ('mid-presence boxes are not trajectories') that consumes space without conveying actionable meaning to an unfamiliar agent.

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?

An output schema exists, so return-value detail is not required, but for a four-parameter transform with zero schema coverage the description should at least anchor each input's meaning and state whether the source scene is modified. Neither gap is closed, so an agent could call it correctly only by guessing.

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 description coverage is 0%, yet the description never maps to the four parameters: it does not explain that 'texts' is an ordered list capped at 32 entries of 500 chars, how 'aspect' (16:9 vs 9:16) interacts with the reflow claim, or what 'duration_ms' does to 'recalculate cadence'. Only a loose thematic hint is offered, leaving the schema's constraints to speak for themselves.

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?

The first clause gives a specific verb and resource: replacing a scene's source copy with supplied text, plus re-timing/reflowing it. That is concrete enough to distinguish it from read-only siblings like get_text_track or get_scene, though the second sentence ('source mid-presence boxes are not trajectories') is domain jargon that does not sharpen the purpose.

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?

There is no statement of when to use this versus alternatives (e.g., get_scene to inspect, suggest_correction to propose changes) and no prerequisites such as where scene_id comes from. The agent must infer usage entirely from the imperative 'Substitute all source copy with your text'.

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