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

Annotations declare non-readonly, non-idempotent, non-destructive, closed-world, but the description adds real behavioral substance: the track is copied once and registered with its licence, it is project-scoped and returns project identity, placement mirrors add_music (whole program by default, ducked under speech, looped to fill), and default gains are disclosed (-18 dB ducked, -4 dB as lead). It does not clarify what happens on an invalid/duplicate slug, which is the one gap for a non-idempotent mutation.

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?

Front-loads the critical PROJECT-SCOPED constraint, then routing, then behavior, with essentially no filler sentences. It is dense and slightly long for a single paragraph, but each clause carries a distinct constraint or default.

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 12-parameter, no-output-schema mutation tool with only 33% schema coverage, the description covers scope, provenance, agent workflow, placement semantics and audio defaults well. It is not fully complete because several numeric placement/fade parameters remain unexplained outside the schema.

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 only 33%, so the description must carry more weight. It explains slug provenance, the gain_db default of -18 dB, duck semantics, and loop-to-fill, but leaves start, end, purpose, fade_in_s and fade_out_s undocumented in both places. Baseline 3 is appropriate given partial compensation for a low-coverage schema.

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?

States a specific verb+resource (place a CC0 library track by slug) and immediately differentiates itself from siblings by naming list_music_library as the source and add_music as the placement analogue. An agent can tell this apart from add_music, swap_music, or list_music_library without opening any schema.

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 routing rules: get the slug from list_music_library, never choose music yourself, offer 2-4 tracks via ask_user and place the one the user picks, with a concrete exclusion ('a mood or some music is not a pick'). This is a genuine when/when-not with a named alternative tool.

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