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

Annotations already declare readOnlyHint=true, idempotentHint=true and openWorldHint=false, so the safety profile is covered. The description adds real context beyond them: the data-scope restriction that only the signed-in customer's own invoices are visible, which is an authorization/data-visibility disclosure the annotations do not convey.

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?

Two tight sentences, zero filler. The returned-field inventory comes first and the access-scope caveat second, both front-loaded where an agent will read them.

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 usefully enumerates the returned fields, which is exactly what an agent needs to know what comes back. Minor residual gaps: ordering of results and whether any further paging/filtering exists beyond 'limit' are unstated.

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% — the single 'limit' parameter already documents its default (12) and max (50) in the schema. The description contributes nothing about parameters, so the baseline 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?

Specific verb+resource ('Read the user's gtm.help billing history') and it enumerates exactly what the resource contains: invoice number, date, status, amount, tax, PDF and hosted-receipt links. No sibling tool touches billing, so no differentiation burden exists, and an agent can immediately tell what this returns.

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?

Usage is implied by the description (fetch the signed-in customer's billing history) but there is no explicit when-to-use, when-not-to-use, or named alternative. The visibility constraint ('Only the signed-in customer's own invoices') is a scope limit rather than routing guidance.

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