session_length_report

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

With no annotations, the description carries the burden and adds meaningful behavior: it discloses that the tool performs a cursor walk against GET /me/player/recently-played and consumes quota. This tells the agent the operation is quota-bearing and paginated. It stops short of explicitly stating side effects or return behavior, but the report framing plus quota disclosure is adequate.

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 tight sentences: the first states function and key defaults, the second states the quota/pagination implication of calling it. No filler, no redundancy, and the important information is front-loaded.

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 data source, defaults, and general report contents, and the schema fully covers the parameters. However, there is no output schema, and the description doesn't specify what the 'distribution' is or the shape of the returned stats. It also doesn't distinguish this from session_stats/listening_session_report, leaving moderate gaps.

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%, and the parameter descriptions already define max_items, gap_minutes, and response_format. The tool description only restates defaults like 30 minutes and 150 items, adding no parameter semantics beyond the schema, so the baseline 3 applies.

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 names a specific operation (splitting recently-played history into sessions by inactivity gap) and a concrete outcome (size/duration stats plus a distribution). It is clear on its own, though it does not explicitly differentiate itself from similar sibling reports such as session_stats or listening_session_report.

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 first sentence implies the use case: analyzing recently-played history to identify listening sessions. But the description never states when to choose this tool over session_stats/listening_session_report, what type of question it answers, or when not to use it. The quota note is operational, not usage guidance.

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