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

Annotations already declare readOnly, idempotent, non-destructive, openWorld, and an output schema exists for the return shape. The description adds that a 'best-value pick' is computed, which is mild behavioral value, but says nothing about how ties are broken, pricing freshness, or any rate/auth considerations.

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 the usage trigger, then a compact list of compared fields. The trailing 'No competitor API offers this' is marketing filler that does not help an agent decide or invoke anything.

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 full schema coverage, rich annotations, and an output schema covering the return payload, the description supplies what an agent needs to call it correctly. Only the sibling disambiguation 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 the single plan_ids parameter is fully documented with minItems/maxItems and a pointer to search_plans. The description's '2-4 plans' merely restates the schema constraint, so 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?

States a specific verb ('compare') and resource ('esimgomobile plans') and enumerates the comparison dimensions (price, data, validity, scope, per-GB unit price) plus a best-value output. It never contrasts itself with close siblings like recommend_plan or get_plan_details, so the agent may struggle to disambiguate, but the purpose itself is unambiguous.

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?

'Use when the user is choosing between 2-4 esimgomobile plans' gives a clear triggering condition and a quantity bound. It stops short of naming alternatives (e.g., recommend_plan for open-ended recommendations, get_plan_details for a single plan), which is the only gap.

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