Get a reading statistic

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

With no annotations, the description carries the full burden. It discloses the pre-aggregated nature, the derivation from reading sessions and progress, the scoping to a single chart, and important parameter quirks (e.g., days ignored by session-timeline, conditional extras). It does not describe output format (e.g., image type or data structure), which would be useful, but the core behavioral traits are covered.

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 appropriately lengthy given the complexity of 16 kinds and 7 parameters, but every sentence earns its place. It is front-loaded with the core purpose, then uses clear bullet-like categorization for the kinds, and succinctly notes the optional parameters and their conditions. There is no redundancy or filler.

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 tool with 7 parameters, 16 enum values, multiple conditional parameters, and no output schema, the description is remarkably complete. It explains the scope (personal vs library), all conditional parameters, and the meaning of 'days'. The only minor gap is the lack of explicit output format details, but the description's phrase 'pre-aggregated chart' gives adequate context for an agent to handle the result.

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?

The schema already documents each parameter fully (100% coverage), but the description adds significant semantic value by grouping the enum options into thematic categories (Activity over time, When they read, Pace & finishing, Breakdowns) and by clarifying per-kind parameter applicability (year/week for session-timeline, comparePrevious for progress-funnel, goalBooks for goal-trajectory). This goes far beyond a bare schema listing.

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 uses a specific verb+resource ('Get one pre-aggregated chart of the signed-in user's personal reading activity') and clearly distinguishes from library-wide analytics by naming get_library_statistic. It also enumerates the 16 specific kinds, leaving no ambiguity about what the tool returns.

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 explicitly says to use get_library_statistic when library-wide analytics are needed, and it categorizes the kinds to help the agent choose the right one. However, it does not explicitly mention alternatives like get_reading_sessions or get_reading_progress for raw or per-session data, so the guidance is good but not exhaustive.

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