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

Goes beyond the annotations by explaining what the destructiveHint actually means in practice: the summary is persisted to the reader's account and "replaces any summary saved earlier for the same dates," which also explains why the call is idempotent. The one-year date-span limit adds a constraint no structured field conveys.

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?

Front-loaded with the action and data produced, then routing guidance, then a compact example. No sentence is redundant — even the side note about replacement semantics carries behavioral weight.

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?

An output schema exists, so return shape needn't be described; the description covers scope, persistence side effects, date constraints, and the sibling alternative. Everything an agent needs to select and invoke this correctly is present.

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 coverage is 100%, so the baseline is 3; the description earns above it by restating the year-apart constraint in prose and providing a concrete worked example with all three parameters, including a period_label pattern the schema only gestures at with a max length.

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 ("Builds a summary of the reader's reading between two dates") and enumerates the content covered: books finished, time/pages read, difficulty, highlights. It is immediately distinguishable from get_monthly_reading_summary by the arbitrary-date-range scope.

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?

Explicitly says when to use it ("a review of a period that is not one calendar month, such as a year in review or a season") and names the alternative for the excluded case: "For a single calendar month, use get_monthly_reading_summary." Both routing directions are covered.

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