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

Annotations already declare the safety profile (not read-only, not destructive, closed-world), so the description adds the useful collision semantic: an existing key at the same t is replaced, and its curve is preserved when no ease is supplied. However, the sentence is terse and ambiguous about what happens to the value v on replacement, and says nothing about permissions or failure modes.

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?

Two short sentences with the core action front-loaded and zero padding. The second sentence is compact to the point of being cryptic, but nothing is wasted or redundant.

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 6-parameter mutation tool with no output schema and near-zero schema description coverage, the description is far too thin: it does not explain the value parameter, units for t, valid ease values, or what the tool returns or mutates. An agent would have to guess at most of the call contract.

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 only 17% (only projectId is documented), so the description must carry the burden. It sheds light on t and ease, but v (the keyframe value), clipId, and the meaning of prop beyond its enum are never explained, leaving most parameters semantically opaque.

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: 'Add or replace one keyframe'. The word 'one' implicitly distinguishes it from the plural sibling set_keyframes, and 'replace' distinguishes it from remove_keyframe/clear_keyframes, though neither sibling is named 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?

There is no explicit when-to-use guidance. The agent is not told when to prefer this over set_keyframes (bulk) or how it relates to add_clip/set_animation, and no prerequisites (project open, clip selected) are stated beyond the projectId default.

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