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

Annotations already declare readOnly/idempotent/non-destructive, so the safety profile is covered. The description goes further by enumerating the output content (plan count, providers, cheapest plan, best price per GB, unlimited plan, validities, comparison link), which tells the agent what to expect beyond the structured hints.

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 sentences, front-loaded with the usage trigger, no filler. The second sentence is a dense list of return values, which is informative but slightly heavy; still efficient overall.

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 two-parameter read tool with full schema coverage, annotations, and an output schema, the definition is complete: it explains when to reach for it and what it summarizes. Return-value details partly duplicate the output schema, which is why it isn't a 5.

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 both parameters are fully documented in the schema itself. The description only echoes 'country or region' without adding format or resolution guidance (e.g. how city vs region vs ISO code resolve), so it adds little over the schema.

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 title and description state a specific resource ('travel eSIM costs in a country or region') and scope ('how much choice there is'), and the phrase 'before comparing individual plans' cleanly separates this aggregate-overview tool from plan-level siblings like get_esim_plan and search_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?

The opening 'Use this when someone asks how much a travel eSIM costs... or how much choice there is, before comparing individual plans' gives clear triggering conditions. It stops short of naming the alternative tool or stating explicit exclusions, but the timing cue is unambiguous.

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