add_keys

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

With no annotations, the description carries the full burden and does disclose some behavior: Spine easing curves are auto-written, and values are offsets from the setup pose (Spine semantics). It does not say whether existing keys are overwritten or merged, what replace_animation does, or what permissions/failure modes apply to this mutation.

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?

Dense but almost every clause carries information: purpose first, then per-type key formats, then easing vocabulary. The format is list-like and scannable rather than terse prose, so it earns its length despite being long.

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 an 8-parameter mutation tool with no annotations, no output schema, and 0% schema description coverage, the description is substantively helpful but has real gaps: replace_animation semantics, ease default (sine_in_out), whether bone and slot are mutually exclusive, and whether the target animation must pre-exist are all unaddressed.

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%, so the description must compensate and it largely does, giving per-timeline-type key formats (rotate [t, deg], translate [t, x, y], rgba [t, "RRGGBBAA"], etc.) and the full list of valid easing names. It leaves project, animation, bone, slot, ease defaults and replace_animation undocumented, but the hard part of the input is covered.

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 concrete verb+resource ('Key one timeline') and immediately qualifies the operation with named easing and Spine curve generation. It is distinguishable from siblings like add_bones or add_event, though it never explicitly names those alternatives or clarifies what a 'timeline' is to a non-expert.

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 when-to-use guidance, no statement of prerequisites (must the project/animation already exist?), and no routing to alternatives such as add_bones or add_event. The only conditional instruction is about appending an easing name to a key, which is parameter mechanics rather than usage context.

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