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

Goes well beyond the readOnly/idempotent annotations: it discloses that the user-level balances endpoint aggregates ALL accounts (not just those flagged is_net_worth), that growth metrics use simple average monthly change rather than CAGR so zero-crossing net worth works, that omitted milestones auto-detect the next 3 round-number thresholds, and that subscription plan limits may restrict the date range.

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, followed by return contents, implementation caveats, the sibling alternative, the plan-limit warning, and the page-link hint. Every sentence carries information an agent would otherwise have to guess; there is no 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?

There is no output schema, and the description fills that gap by enumerating what is returned (historical trend, forecast projection, growth metrics, milestone projections). Combined with the annotations covering safety and the routing to cash_flow_forecast, an agent has everything needed to call this correctly.

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 still adds real meaning by scoping milestones to total net worth and clarifying the auto-detection behavior and its alternative tool. It does not add further detail on resolution or months_back/months_ahead beyond the schema's own defaults and plan-limit note.

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 ('Projects net worth trajectory') and defines scope precisely: past history plus future forecast, returning trend, projections, growth metrics and milestones. It is immediately distinguishable from cash_flow_forecast and navigate_to_net_worth, both of which are named.

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 routes the agent: milestones apply to TOTAL net worth only, and per-account target tracking (e.g. an emergency fund hitting $10k) must use cash_flow_forecast with account_ids instead. It also names navigate_to_net_worth as the page link to pair with the answer, so both the data call and the follow-up action are covered.

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