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

Annotations already provide readOnlyHint and openWorldHint. The description adds valuable behavior beyond that: it explains the ordering ('by closeness then by an internal catalogue ordering key (not an audience metric)') and the output richness ('Each returned track carries full audio features'). This is context an agent needs to interpret results and decide on downstream steps, so it adds meaningful transparency.

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 two substantive sentences plus a final combination hint. The core purpose is front-loaded in the first sentence, and every subsequent clause adds useful context (ordering, use cases, audio features, key combination). There is no fluff or redundancy, and it stays compact.

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 an output schema present, the description doesn't need to detail return fields. It covers the matching rule, ordering, use cases, and how to extend with find_tracks_by_key. The safety profile is handled by annotations (readOnlyHint). Nothing an agent needs to invoke and interpret the tool correctly 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 coverage is 100%, so all three parameters (bpm, limit, tolerance) are already documented with descriptions. The description reiterates the tolerance concept ('within +/- tolerance of bpm') and ties it to ordering, but it doesn't add new syntax or format details. The baseline for high schema coverage is 3, and the description adds only marginal value, so 3 is appropriate.

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 opens with a specific verb and resource: 'Find catalog tracks near a target tempo.' It clearly states the matching rule (BPM within +/- tolerance) and the ordering, and it explicitly references the sibling tool find_tracks_by_key for key-based filtering, which distinguishes it from that alternative. The purpose is unambiguous and distinct.

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 provides clear usage context: 'useful for DJ set planning, workout playlists, or tempo-matching.' It also gives an explicit alternative condition: 'To also constrain by musical key, combine with find_tracks_by_key.' It lacks a direct 'when not to use' for other siblings like search_catalog or get_recommendations, but the combination hint and the tempo-specific focus give sufficient guidance.

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