Derive animation variant

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

Annotations only declare readOnlyHint=false and destructiveHint=false, so the description earns credit for adding that the write is validated, backed up and verified, and that it is a dry-run unless `apply` is set. That safety/dry-run disclosure is real value beyond the structured fields, though it doesn't say what happens if `name` collides with an existing animation or how the backup can be restored.

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 dense sentence with the core behavior front-loaded and no filler; the parenthetical keeps the safety details compact. The trailing doc-link fragment is terse but arguably wastes space since it points to content not included.

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?

This is a complex mutation tool: 11 parameters, an 18-way oneOf op vocabulary, no output schema, and 18% schema description coverage. Deferring all op semantics to an external anchor leaves the definition incomplete for correct invocation, and it also omits what the tool returns and how failures/validation errors surface.

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?

Wrong scale: schema description coverage is 18% across 11 parameters, so the description must compensate. It only clarifies `apply` (dry-run semantics) and the ordering of `ops`; `project`, `source`, `name`, `skeleton`, `editor`, `stagingPath`, `replace`, `allowUpgrade` and `loopAnimations` are left entirely to an undocumented schema, and the 18 operation variants are delegated to an external 'docs/USAGE.md#derive-operations' anchor the agent may not be able to read. A 2 reflects that the description adds almost no parameter meaning.

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: 'Builds a new animation from an existing one' with ops applied in order. It also positions itself relative to a sibling by saying the result is added 'like spine_add_animation', which helps an agent distinguish derivation from plain creation, though it never names the sibling it should be preferred over (e.g. spine_generate_animation, spine_transfer_animation) 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?

Gives the operating context ('ops applied in order on the server', 'dry-run unless apply') but never states when to choose this over spine_add_animation or spine_generate_animation, nor any prerequisite such as the source animation existing or the project being open. Usage is implied through the sibling reference rather than spelled out.

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