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

Annotations already declare readOnlyHint=true and the description reinforces it with 'READ'. It adds valuable context beyond annotations: project-scoped behavior ('acts only on the explicit project_id and returns the project identity with its result'), license verification, commercial use terms, and that it marks tracks already used by the user. It doesn't cover pagination or return format, but with annotations and no output schema, the description carries most of the load well.

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 front-loaded with the key scoping constraint ('PROJECT-SCOPED') and then the read/action. It's fairly dense but every sentence adds information about the tool's purpose, licensing, and workflow. Minor redundancy with schema (mood slugs), but overall efficient.

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 read-only listing tool with annotations covering safety and a 100% schema, the description provides all necessary context: project scoping, what it returns (project identity), licensing, commercial use rights, and how it integrates with ask_user/add_library_music. No output schema, so explanation of return values is minimal but sufficient (mentions identity and marks used tracks).

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%, so the schema already documents both parameters, including the enum for mood and a detailed description for project_id. The description adds the list of mood slugs, which is redundant with the enum but could help an agent parse, and emphasizes project_id scoping. Baseline 3 is appropriate when the schema does the heavy lifting.

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?

Description states a specific verb+resource ('List the built-in CC0 music library by mood') and scopes it as READ. It clearly distinguishes itself from add_library_music (which places a selected track) and list_sound_library/list_assets. However, it doesn't explicitly name those siblings, so differentiation requires the agent to infer from the workflow mentioned.

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?

The description explicitly says it provides 'exact slugs to offer the user with ask_user (add_library_music places the one they pick)', directly specifying the workflow: use this to list, then ask_user, then add_library_music. This is a clear when-to-use with the follow-up action named.

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