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

Annotations already declare this as a non-read-only, non-idempotent write with no open-world access. Beyond that, the description adds real behavioral context: it is project-scoped to an explicit project_id and echoes back project identity, and it discloses morphing semantics (same id across scenes = one morphing object, from=<id> iris transitions) and data-provenance rules. 'WRITE:' merely restates readOnlyHint=false.

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 scope and write nature are correctly front-loaded, but the bulk is a dense wall of bracketed DSL tokens (scenes=[{...}], objects:[{...}], media={...}) that is hard to parse and mixes syntax, behavior, and constraints. Every clause is informative, yet the packing costs readability.

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 10-param nested write tool with no output schema, the description covers the core scenes/media structures and the required project scoping. It is silent on time framing (start/end), theming (theme/accent, id), and any failure/validation behavior, leaving meaningful gaps for an agent composing a call.

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 30% across 10 params, so the description must compensate, and it does explain the scenes DSL, layout values, object kinds, bind/state, media slot format, and the backdrop enum. However, it leaves several top-level params (start, end, theme, accent, id) and many nested object fields (title, body, value, delta, rows, etc.) to the schema, so the compensation is partial.

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 specific purpose — building an 'explainer told through interface' — and the object kinds (card, pill, comment, metric, bars, window, media, text) make concrete what a UI scene contains. It does not name the sibling it contrasts with (e.g. add_title_card, add_typeset, set_typography_scene), so sibling differentiation is left to the reader.

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 a hard constraint ('numbers come only from data... never invented') and a scope note, but no statement of when to choose this tool over the many adjacent add_* / set_* typographic tools. An agent must infer the 'explainer-through-interface' niche on its own.

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