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

Annotations already declare readOnly, idempotent, non-destructive, closed-world behavior, so the safety profile is covered. The description adds meaningful context beyond that: the dual-key requirement, the constraint that both identifiers must match the same order, and the enumeration of possible status values.

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 what it returns, followed by requirements and usage triggers. The parenthetical explaining ICCID is slightly verbose but earns its place by helping an agent locate the value; overall efficient with no filler.

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 return-value burden and does so by listing all returned fields and status values. It omits error behavior (e.g. what happens when identifiers don't match an order), which is a minor gap for a lookup tool.

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 baseline is 3, but the description adds real meaning: ICCID format (long number starting 89, found in order email and phone settings) and that the email must be the one used at checkout. It also explains the cross-parameter constraint that both must belong to the same order.

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+resource (check eSIM status) and enumerates exactly what is returned: data used/left, plan size, expiry, status values, and auto top-up state. This is clearly distinguishable from siblings like check_phone_compatibility or get_esim_plans.

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?

Gives explicit trigger scenarios ('how much data they have left or why their eSIM stopped working') and prerequisites (email AND ICCID must match the same order). It does not name alternative tools or state when NOT to use it, so it falls short of a 5.

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