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

Annotations already indicate a non-readonly, non-destructive operation. The description adds meaningful behavior: unmatched songs are excluded and reported, and sign-in triggers a preserved request with one retry. These details go beyond the annotations and clarify side effects, with no contradiction.

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?

Three sentences front-load the core purpose and then present conditions. No fluff or redundancy; it efficiently conveys the essential action and constraints.

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 description covers the main action and constraints, and the output schema handles return values. However, it does not explain the pendingActionId parameter or specify prerequisites like an active session. For a tool with four parameters and no required ones, more detail is needed for an agent to call it reliably.

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?

With 0% schema coverage, the description must compensate for parameter documentation. It explains the service parameter's conditional use and hints at sessionId via 'one listening session', but leaves name and pendingActionId unexplained. This is a significant gap given the schema provides no descriptions.

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 clearly states a specific verb (save), resource (matched music from one listening session), and result (private playlist in active music service). It implies a distinction from create_playlist by focusing on a session's matched songs, but does not explicitly name the alternative.

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?

Provides explicit guidance for the service parameter (only pass when the listener explicitly names Spotify or Apple Music) and mentions a safe retry on sign-in. However, it does not state when to use this tool versus siblings like create_playlist, leaving that decision to inference.

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