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

Beyond the readOnly/idempotent annotations, it discloses meaningful edge-case behavior: `suppressed: true` means under half of revenue carries a customer id and figures must be withheld, a null CAC means no spend or fewer than 10 new customers and is never zero, `support: null` means no helpdesk connected, and `paidGaps` names excluded platforms. It also states the default window is the last 30 days and that each tile carries a `previous` prior-period value.

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?

Information-dense with almost no filler — every clause defines a metric, a null/suppression rule, or a date constraint — and usage guidance about not dividing ratios yourself is front-loaded. The main weakness is structural: it is one long run-on paragraph where the metric enumeration, the edge-case rules and the date-span rules blur together, making it harder to scan than a bulleted layout would be.

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 carries the full burden of describing return values, and it does so exhaustively — naming nested paths (acquisition.acquisition, acquisition.lapsedAtStart, ltvBands, growth) and explaining null/suppressed semantics. For a 2-optional-parameter read tool, nothing an agent needs in order to call it or interpret the response is missing.

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 on top: `from`/`to` are inclusive YYYY-MM-DD, must be sent both or neither, can never be after today, and replace the default 30-day period — with the strong operational rule that an operator-named month or week MUST be passed here. The schema's own descriptions already carry much of this, so the gain is incremental rather than unique.

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 names a specific resource (customer figures for the current period) and enumerates the exact metrics returned: total/new/returning customers, repeatPurchaseRate, avgLtv, marginLtv, blended CAC, paidCac, ltvBands, growth, acquisition.acquisition, acquisition.reactivated and support. It even disambiguates Shopify's returningCustomers (orders) from returningBuyers (headcount), so an agent knows precisely what it gets without opening a schema.

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?

Explicit when-to-use coverage: 'Use for any question about customers, LTV, CAC, repeat purchase, acquisition by channel or LTV ÷ CAC', plus a clear prohibition on self-computing ratios and a rule to send operator-supplied months/weeks/date pairs here. It does not route to any named sibling (e.g. get_customer_lifetime, get_sales_breakdown), so the alternative-selection guidance 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.