Compare two animations

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

readOnlyHint=true already tells the agent this is a safe analysis operation. The description adds genuine value by disclosing the result contents and sort order ('biggest first') and by flagging that contact sheets are optional, but it says nothing about cost, limits, or failure modes when the two clips are incompatible (different skeletons, mismatched lengths).

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?

A single telegraphic sentence, front-loaded with the operation and then the reported fields; nothing is redundant. The colon-and-semicolon listing style is dense but readable and well ordered.

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?

With no output schema, the description usefully enumerates return contents, which is the right call for an 8-parameter tool. However, half the parameters remain unexplained and there is no note on the ~8s render cost beyond the schema's own hint, so an agent still has to inspect the schema to call it correctly.

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 only 50%: b, fps, bones, and limit are undocumented in the schema, and the description does not explain any of them — one can guess b is the second clip from 'A/B', but bones/limit/fps semantics and their interaction are entirely unstated. The description's mentions of per-bone changes and contact sheets loosely map to bones and render but add no parameter guidance.

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 description states a concrete operation — an A/B comparison of two animations of one skeleton — and enumerates what the comparison reports (duration, motion ratio, per-bone deltas, timing structure). That distinguishes it from neighbors like spine_measure or spine_timing, though it never names those siblings explicitly.

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 by 'A/B of two animations of one skeleton'; an agent can infer this is the diff tool, but there is no explicit when-to-use versus spine_measure, spine_timing, spine_mix_check or spine_motion_visual, and no stated preconditions (e.g. both animations must live in the same skeleton/file).

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