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

Annotations are all false, so the description carries the full burden. It discloses that the call is project-scoped, returns the project identity, uses program-time windows, and advises previewing the whole path before accepting. This gives the agent a clear sense of side effects and scope, though it doesn't state whether it replaces or adds to existing graphics or detail error conditions.

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?

The description is a single dense paragraph, but every sentence adds value: scope, action, kinds, coordinate system, formatting rules, motion, and usage philosophy. It is front-loaded with the project-scoping caveat and avoids filler. Slightly long but efficient for the parameter complexity.

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?

Given 17 parameters, nested motion objects, and no output schema, the description covers most parameter semantics and usage context. It lacks explicit units for start/end (seconds vs frames) and does not explain motion_motif or the top-level opacity (though motion includes it). These are minor gaps given the richness of the rest, so it is nearly complete.

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?

With schema coverage at only 18%, the description compensates well: it explains x/y as frame-fraction centres, width/height as fractions, color formats (#RRGGBB), stroke_width as a fraction of the short edge, rounding as 0-0.5 of the short side, and progress value as 0-1. It also explains motion uses the same keyframe structure as designed text. It does not explicitly describe start/end units or the motion_motif parameter, but most critical semantics are 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?

The description clearly states it adds a renderer-native VECTOR graphic over a program-time window, enumerates the supported kinds (rectangle, ellipse, line, arrow, ring, progress) and distinguishes them by purpose. This is a specific verb+resource with enough detail to separate it from sibling add_* tools like add_text or add_overlay.

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?

It provides explicit guidance on when to use each shape ('use a panel to support hierarchy, a line to connect, and arrows/rings only when the frame contains the thing they identify') and notes the project-scoped nature. However, it does not explicitly name alternatives or state when not to use this tool (e.g., versus set_vector_graphic), so the exclusion context is only implicit.

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