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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false and openWorldHint=false, so safety is covered. The description usefully adds the seat-vs-account scoping distinction, but says nothing about response shape, units, or the default look-back beyond what the schema states.

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, front-loaded with the returned resource and followed immediately by the one non-obvious parameter behavior. No filler, though the second sentence is terse enough to feel slightly clipped.

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?

For a read-only, two-parameter tool with no output schema, the description covers the core purpose and the ambiguous flag. It omits what fields come back and how 'days' bounds the totals, so an agent lacks a little context for interpreting results.

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 50%: 'days' is documented in the schema, but 'company' has no schema description. The description compensates for 'company' by explaining it means whole-account scope on Business, which is the useful bit; still, no detail on how days interacts with either scope.

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 (Returns) and resource (eSIM data balance and minutes used), and pins the scope to 'this seat' vs 'the whole account'. It is clearly distinguishable from get_account_balance and get_data_rate by the seat-level framing, though it never names a sibling to route away from.

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 'company=true covers the whole account on Business' note implies when to use the account-wide variant, but there is no explicit when-to-use, when-not, or alternative-tool guidance against the many get_*/quote_* siblings. Usage is only implied.

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