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

With readOnlyHint=false already flagging a mutation, the description still adds real value: it says content is appended rather than replacing the timeline, that scenes land as PENDING prompts with nothing generated, that text timing is included, and that the operation is FREE. It does not cover what happens to conflicting existing tracks or whether applying twice stacks templates.

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, cost, and template catalog appear in that order, so the actionable content is front-loaded. The catalog is long but each entry disambiguates a distinct enum value, so it earns its space; a parenthetical cost tag ('FREE') as a standalone sentence is slightly clipped.

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 two-parameter mutation with full schema coverage and no output schema, the description covers effect, state of created content, cost, and template choice. The only real gap is the return value (e.g., which scenes/tracks are created and their identifiers), which is not inferable without an output schema.

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 project_id and the enum are already documented, but the schema's template_id gloss is only 'Which choreography to apply.' The description supplies the missing semantic layer — aspect ratio and intended use for all eight template values — which directly aids enum selection beyond what the schema provides.

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 opening sentence states a specific verb and resource: 'Append a stored choreography ... onto this composition', and immediately clarifies the resulting state ('scenes as PENDING prompts, nothing generated yet'). That distinguishes it from scene-level siblings like studio.add_scene or studio.generate_scene, which act on one scene rather than applying a whole stored template.

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 only implied. 'FREE' signals a cost-based reason to prefer this over generated alternatives, and the per-template blurbs help the agent choose a template_id, but the description never says when to use this instead of add_scene/apply_ops or states any precondition (e.g., empty composition vs. existing timeline).

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