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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false, so safety is covered. The description adds genuine non-obvious behavior: the chart renders per-period actual bars, a budget overlay, an average line and a rollover band, and the bucket count is derived from range ÷ width rather than supplied. It does not clarify what the 'deep link' returns, but for a read-only navigation tool that is a minor omission.

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 core definition before usage examples and alternatives, and every sentence carries routing or semantic information. It is a dense single paragraph, though — the quoted example phrasings could be trimmed without losing routing value.

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?

Nine parameters (all optional), no output schema, and full schema coverage — the description still covers the gaps that matter: which sibling to pick, how the window is bucketed, how to resolve a category, and how to model a two-period comparison. Nothing an agent needs to call this correctly is missing.

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, and the description earns above that by disambiguating the most error-prone parameter — period_quantity is the bucket width multiple, NOT the bucket count — and by stating that omitting category_id means all categories combined and that type selects income OR expense. It also prescribes list_categories to resolve a name to an ID, which the schema does not say.

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?

Opens with a specific verb+resource ('Deep link to the Trends report') and immediately scopes it: one category's spending/earning over time, or all categories combined when category_id is omitted. It explicitly separates itself from navigate_to_income_expense and navigate_to_budget, so an agent can route without opening the schema.

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?

Gives the selection rule ('Pick this for over-time / comparison / history asks'), four concrete user-phrasing examples, and named alternatives with the conditions that select them (multi-category one-period breakdown → navigate_to_income_expense; budget management → navigate_to_budget). It even handles the edge case of comparing two periods by prescribing one custom window with monthly buckets.

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