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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so the description's 'Reads only' is redundant; however 'costs nothing' adds useful cost context not present in annotations. It also discloses non-obvious behavior — topic marks best fits rather than filtering, and mood actually filters — which is meaningful behavioral nuance.

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?

Three tight sentences: what it returns, how to use topic, then when to use it and where to hand results off. The routing information is front-loaded and every clause carries information.

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 fills that gap by describing the return shape (tracks grouped by mood with listen links) and the marking behavior. Combined with the explicit handoff to create_video, nothing needed to invoke or act on the result is missing.

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 100% and the enum for mood is fully documented, so the schema already carries both parameters. The description restates the filter-vs-mark distinction ('Pass a topic to have the best fits for it marked') without adding format or syntax detail beyond it, matching the baseline for high coverage.

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 resource (background music tracks a video can use) and its organization (grouped by mood, each with a listening link). The phrase 'background music tracks a video can use' clearly distinguishes it from siblings like list_presenters or list_characters.

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?

Explicit triggers are given: 'when the user asks for music, wants to choose a track, or asks what moods exist.' It also names the downstream consumer (create_video as music) and what to pass it, so the agent knows the follow-up action.

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