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

Annotations already declare read-only, idempotent, non-destructive, closed-world, so the safety profile is covered. The description adds genuinely useful non-obvious behavior: a Last Price credential is required and self-registered sandbox keys get a 403 until the workspace is claimed. It stops short of stating rate limits or result-size behavior, but the auth gates are a meaningful addition.

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 purpose and aggregation detail, then the period parameter, then the two hard prerequisites. It is dense but every clause is relevant; the only mild redundancy is the explicit instruction to pass start_date and end_date, which the schema already conveys.

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, so the description carries the burden of explaining results, and it does by enumerating per-group and per-currency count/total/average/min/max plus overall totals. Auth and workspace-state requirements are covered. Only pagination/row-limit behavior is unaddressed.

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% and every parameter has a description, so the baseline is 3. The description restates the group_by default of 'day' and confirms that start_date/end_date delimit the period, which the schema already says; it adds no format or boundary semantics beyond that.

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 ('Total the costs recorded in your workspace over a period') plus the grouping dimensions and aggregate statistics produced. It implicitly separates itself from the sibling list_costs by being an aggregation rather than a row listing, but never names an alternative explicitly.

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?

'Pass start_date and end_date to choose the period' gives the calling pattern, and the credential/claimed-workspace prerequisites are spelled out. However, there is no guidance on when this aggregation is preferable to list_costs or get_usage_breakdown, nor any exclusion of cases where it should not be used.

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