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

Annotations already establish this is a read-only, closed-world operation, so the description doesn't need to re-establish safety. It adds one genuinely useful behavior: mood-based ranking applies only to themes and pairings. It does not disclose what is returned (names only? ids?), whether ordering is defaulted, or how limit interacts with results.

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?

Two tight sentences, front-loaded with the core listing capability, and the enumeration is directly useful prose even if it overlaps the enum. No filler or hedging.

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 browse tool with no output schema and 0% schema description coverage, the description leaves meaningful gaps: the return shape, the meaning of `mode` (light/dark filtering?), and limit behavior/defaults. It is adequate to start a call but not fully self-sufficient.

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 coverage is 0%, so the description has to carry parameter meaning. It does add real semantics for mood (concrete example values, and the crucial constraint that it ranks only themes/pairings) and partially explains `what`. But `mode` and `limit` are never mentioned in the description and are undocumented in the schema, leaving half the parameters opaque.

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?

A concrete verb ("List") plus the exact resources it enumerates, which distinguishes it from the singular get_* siblings (get_theme, get_family, get_pairing). However, the prose list omits the enum values "motion" and "scales" that the schema actually accepts, so the stated scope is slightly narrower than the tool's real scope.

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 second sentence implies how to use the mood parameter (ranking themes/pairings), giving some usage context. But it never states when to choose browse_library over get_theme/get_family or search_pieces, and gives no exclusions or prerequisites.

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