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

Beyond the annotations (readOnly/idempotent/non-destructive), the description discloses two non-obvious behaviors: historical forecast values reflect CURRENT scenario settings rather than what was originally forecast, and accounts without linked scenarios return no comparison data. These are exactly the caveats an agent needs to interpret results correctly and avoid misleading conclusions.

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?

Purpose is front-loaded in the first sentence, the qualification caveats follow, and every sentence adds information — the 25%+ and 2x+ thresholds and the scenario-settings note are all load-bearing. No repetition of the title or schema.

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 does the work of explaining what the analysis produces (balance comparisons plus categorized inaccuracy drivers) and flags the empty-data case. It stops short of describing the shape of the returned comparison data, which is the only remaining gap for a zero-required-parameter analytical tool.

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%, so all four parameters (user_id, resolution, account_ids, months_back) are already documented including defaults and the max of 12. The description adds no parameter-level detail, so the baseline of 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 opens with a specific verb and resource: compares actual vs forecast account balances over past periods. It then adds a second, distinct capability (budget inaccuracy drivers with explicit thresholds) and implicitly distinguishes itself from forward-looking siblings like cash_flow_forecast and net_worth_forecast by being a retrospective evaluation.

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?

It states the use case clearly — 'useful for calibrating current forecast configuration' — which tells an agent when to reach for it. However, it never names an alternative tool (e.g. cash_flow_forecast vs this) or states when not to use it, so routing between the several forecast-related siblings still requires inference.

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