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

Annotations already mark the tool as read-only and idempotent. The description adds useful semantics: upgrades replace the plan rather than adding to it, and more high-speed data does not mean faster network speed. It does not describe the return shape, and there is no output schema.

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?

Three short sentences, with the purpose stated first. Each sentence carries distinct information.

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?

It covers purpose and the key semantics of what an upgrade means. It lacks documentation of the return contents and of the planId source, which matters because there is no output schema and parameter coverage is low.

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 25%, and only 'days' has a description. The description never explains planId (where it comes from), currency format, or locale. 'Selected plan' gives weak indirect meaning to planId, which does not make up for the coverage gap.

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?

It names a specific action and resource: finding verified data and extra-coverage upgrades for a selected plan. 'For the selected plan' implies it follows get_esim_plan or list_esim_plans, but it doesn't explicitly set itself apart from siblings such as compare_esim_prices.

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?

Context is implied: use it after a plan is selected. It adds presentation guidance ('Show only available upgrades and the added countries'). There is no explicit when-not-to-use guidance and no pointer to siblings for the prerequisite planId.

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