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

Annotations cover only readOnlyHint and openWorldHint, and the description adds substantial behavioral context beyond them: currency is MYR with foreign invoices converted at the invoice-frozen rate, credit notes are excluded so returns are not netted, and the two tax bases are disclosed with exactly which payload fields are tax-inclusive vs. ex-tax. This is precisely the kind of trap-avoiding detail an agent needs and cannot get from the schema.

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 meaning, then layered detail in decreasing priority. Every sentence carries real information (currency basis, credit-note exclusion, tax bases), though the closing imperative about quoting one basis is advisory framing rather than tool semantics and could be trimmed without loss.

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 must describe the return shape — and it does, naming byMonth, byCustomer, byProduct and the total/exTax fields and their differing tax bases. Combined with the mode explanation and exclusion rules, an agent has everything needed to invoke and interpret the result 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 description coverage is 0% for `from` and `to`, so the description carries the semantic burden — and it does explain that omitting them yields today/month-to-date while supplying a range yields that period's invoiced sales. It does not restate the YYYY-MM-DD pattern, but that is already in the schema, so the gap is minor.

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 ('How much you have sold') and immediately defines the two operating modes — no dates yields today plus month-to-date, a date range yields invoiced sales for that period. It further specifies the breakdown dimensions (month, customer, product), so an agent knows exactly what this returns and how it differs from sibling summaries like expenses_summary or income_statement.

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?

The description clearly states the two usage contexts (no dates vs. with a date range), which effectively tells the agent when each behavior fires. What it does not do is name an alternative sibling (e.g. income_statement or financial_timeseries) or state when NOT to use this tool, so it stops short of the explicit routing found in the best definitions.

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