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

Annotations already cover read-only/idempotent/non-destructive, and the description adds a genuine non-obvious detail — 'Requires: demos:read' — plus the fact that authoring rules for hand-written scene HTML are included in the response. It does not state the response shape or ordering, but with no output schema the enumerated look catalog compensates substantially.

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?

Roughly 250 words for a zero-argument list tool, with six long parenthetical mini-essays describing each look's visual style and target audience. The single most important clause — that this returns the available scenes/looks — is buried in a sentence fragment rather than front-loaded, and the marketing-style scene-setting ('words blurring into focus', 'a drifting light leak') is not what an agent needs to select or invoke the tool.

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?

With no output schema, the description must convey what comes back, and it does enumerate the six looks and mention authoring rules. But it never explains how blocks are identified (name slugs? ids?), what the authoring-rules content actually looks like, or whether scene blocks and looks are separate collections in the response — gaps an agent needs closed to chain into write_scene or update_video.

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?

The tool takes zero parameters, so the description has no parameter burden to carry; baseline is 4. Nothing in the text misleads about inputs.

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 is a noun phrase naming the resource ('ready-made scenes ... and its looks ... plus the authoring rules') but never states the verb — nothing says it lists or returns them, despite the tool name and title both saying 'list'. It does differentiate well from siblings by referencing add_scene, write_scene, and update_video, which is the strongest part of its clarity.

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 gives concrete relational guidance: add_scene fills a scene block with values, write_scene can start from one, and the looks are presets for update_video — this effectively tells an agent how the returned data is consumed downstream. It stops short of an explicit call-to-action ('call this before write_scene to discover valid looks') and names no when-not-to-use conditions.

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