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

Annotations already declare readOnlyHint, idempotentHint, non-destructive and closed-world, so the safety profile is fully covered. The description adds genuine context beyond that: only *approved* bills are counted (excluding pending/rejected invoices) and the window is bounded/trailing rather than open-ended. It does not disclose defaults (12 months) or the 24-month cap, which the schema carries instead.

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?

One tight sentence with the resource front-loaded and the qualifiers ('approved-bill', 'bounded trailing period') following immediately. Nothing is redundant, but for a tool with no output schema and an undocumented parameter, a single clause leaves it on the thin side.

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?

With no output schema, the description should convey what comes back — e.g. whether results are a single grouped breakdown or per-month series, and whether counts or amounts. 'By currency, vendor, category and month' gestures at grouping but leaves the response shape ambiguous, and no prerequisite or scoping notes (workspace-wide? entity-filtered?) are given.

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 single parameter has 0% description coverage in the schema, though min/max/default (1–24, default 12) are structurally present. The phrase 'bounded trailing period' hints that the input is a lookback window measured backwards from today, but the description never names 'months' or states that the count is in months and caps at 24, so it only partially compensates for the coverage gap.

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 ('Read') and a precisely scoped resource ('approved-bill spending'), then enumerates the four aggregation dimensions (currency, vendor, category, month). This distinguishes it in substance from get_spend_invoices (raw invoice list) and get_budget_actuals, but it never names those siblings explicitly, so the differentiation must be inferred.

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?

'Over a bounded trailing period' implies the usage context (period-based rollup, not a full-history query), but there is no explicit when-to-use guidance and no mention of when to prefer get_spend_invoices, get_budget_actuals, or get_cash_flow instead. Usage is implied rather than stated.

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