check_in_library

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

Annotations are absent, so the description carries the behavioral disclosure burden. It discloses the response shape ('Returns a boolean per URI'), the endpoint type ('Spotify's unified endpoint'), the accepted URI mix, and the batch limit (Max 40). It implies read-only behavior via 'Check', though it does not explicitly say it has no side effects.

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 compact and front-loaded with the most important guidance ('Preferred'), followed by scope, behavioral distinction, output, and limit. Every sentence contributes either selection guidance or call semantics.

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?

The tool is simple and the schema covers all parameters, while the description covers output shape and the main sibling distinction. It could add batching/pagination guidance for more than 40 URIs, but nothing essential is missing for correct invocation.

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 uris, max_results, and response_format. The description adds useful context around accepted URI kinds and the 40-item cap, but does not add meaningful semantics beyond what the schema already provides.

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 and resource: 'Check whether items are saved in or followed by the user' and clarifies it tests 'LIBRARY-SAVED/FOLLOWED state'. It explicitly distinguishes itself from check_following_artists, so an agent can tell the tools apart without opening schemas.

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?

Description is explicit about when to prefer this tool ('Preferred', 'widest URI mix ... in one request'), names the alternative it should not be confused with (check_following_artists), and routes mutation intent to follow_artists/unfollow_artists. This gives clear selection guidance.

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