download_song

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

No annotations are provided, so the description carries the full burden. It discloses download behavior but doesn't mention key behavioral details like whether files are overwritten on conflict, what the output/return format is (though output schema exists), whether it requires authentication, or error conditions. For a file-writing operation with zero annotation coverage, the transparency is limited.

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 sentences, zero filler. The first sentence states the core purpose and parameter modes. The second sentence explains the default behavior for an optional parameter. Every word earns its place. Excellent concision.

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?

Given the output schema exists (structuring the return), the description doesn't need to explain return values. However, this is a file-mutation tool with 4 parameters at 0% schema coverage and no annotations. The description covers the essential parameter logic (either/or modes, default dir) but lacks behavioral context like conflict handling and prerequisites. Slightly above minimum viable but incomplete for a download/mutation operation.

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 0%, and the description only partially compensates. It explains the relationship between norm_key and title+artist (either-or), and that target_dir defaults to a config value when omitted. But it doesn't explain the format of norm_key, whether title/artist must both be provided together, or constraints on directory paths. At 0% schema coverage, the description should do more heavy lifting for all 4 parameters.

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 verb+resource ('下载歌曲到本地' - download song to local). The purpose is clear: downloads a song to local storage. It doesn't explicitly distinguish from siblings, but siblings like search_songs, get_lyrics, scan_library are obviously different in function, so the differentiation is reasonably clear from the nature of the action.

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 provides clear usage guidance: pass norm_key (from search results) OR title+artist. It also explains that target_dir defaults to MUSIC_MCP_DOWNLOAD_DIR config when omitted. This gives the agent clear direction on parameter selection. However, it doesn't explicitly state when NOT to use this tool versus alternatives, though the distinction is fairly apparent.

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