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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered. The description adds useful behavioral context about currency: prices default to USD outside Nigeria and NGN inside Nigeria, and the caller can override with the currency parameter.

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?

A single sentence, front-loaded with the core operation and immediately followed by the id example and currency rule. No wasted words or redundant restatement.

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?

Given no output schema, the description adequately explains what is returned: full details including every plan and price for the destination encoded by the id. It also explains the currency default behavior. Minor gaps like invalid-id handling or pagination are not covered, but the essential context is present.

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%, so both parameters are already documented in the schema. The description reinforces the id example ('esim:GB') and clarifies that fetching it returns 'every plan and price for that destination,' but most parameter detail duplicates 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 description gives a specific verb-resource pair: 'Full details for one id returned by search,' and even limits scope to a specific example id type ('esim:GB'). It clearly positions itself as the follow-up lookup for a search result, though it does not explicitly name sibling tools like search_esim_plans or list_esim_locations.

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 phrase 'id returned by search' implies the correct workflow: use search first, then fetch with one of its ids. There are no explicit exclusions or named alternative tools, so the guidance is clear but not exhaustive.

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