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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so the safety profile is fully covered by structured data. The description's added content ('Covers iPhone and Android, via QR code or manual entry') merely restates the two enum parameters rather than disclosing anything new about behavior. With an output schema present, no return-value explanation is required, so a baseline 3 is right.

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 short sentences, zero filler, with the trigger condition front-loaded and the coverage scope second. Every clause earns its place.

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?

This is a simple read-only, closed-world, idempotent lookup with two fully documented enum parameters and an output schema, so the description covers what an agent needs to invoke it. It could be marginally stronger by stating the sibling boundary against troubleshoot_esim, but nothing essential 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 description coverage is 100% and both parameters are enums with constrained values, so the schema carries the parameter burden. The description's mention of iPhone/Android and QR/manual maps directly onto those enums without adding format or usage nuance. 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?

The description names a specific resource (step-by-step eSIM installation instructions) and a clear trigger verb ('Use when the user needs...'), so an agent knows exactly what it returns. It does not, however, differentiate itself from close siblings like troubleshoot_esim or setup_dual_sim, which an agent could plausibly confuse with an install-instruction request.

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 'Use when...' clause gives a clear selection condition tied to the user's need for installation instructions. There is no explicit when-not guidance or named alternative (e.g., route troubleshooting problems to troubleshoot_esim), so it stops short of the top score.

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