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

Annotations only state it is not read-only, not idempotent, not destructive. The description goes well beyond that: it explains the reframing behavior (point/face/active-speaker focus), that the source's authored intent is copied, that a NEW INDEPENDENT composition is saved in the same project (source untouched), and what is returned. It also routes the agent onward to create_render or apply_composition.

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 action and payload before the supporting detail, and the trailing parenthetical carries genuinely useful disambiguation rather than filler. It is dense and slightly long, but each clause (behavior, return value, follow-up tools, exclusion) earns its place.

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 nested-body mutation tool, the description covers invocation shape, side effects on the source, reframing behavior, and the return value, and an output schema exists for the return contract. Nothing an agent needs to call it correctly is missing.

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 still adds value by spelling out the body shape (fromCompositionId + targetFormat with aspectRatio/fps/resolution) and by clarifying the semantic distinction between targetFormat here and create_render.format, which the schema alone does not convey.

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 ('Derive') and a precise resource ('a reframed SIBLING composition for a different aspect ratio'), and explicitly names the feature (Auto-Reframe / Magic-Resize). It clearly differentiates itself from create_render and apply_composition, both of which appear as siblings.

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?

Gives an explicit positive use case ('make 9:16 + 1:1 + 4:5 cuts from one 16:9 edit') and an explicit exclusion with the correct alternative ('to only change resolution within the SAME aspect, pass create_render.format instead'). When-to-use and when-not-to-use are both covered.

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