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

Annotations already declare readOnly=true, destructive=false and closed-world, so safety is covered. The description adds real behavioral context beyond them: pagination is driven by meta.has_more and cursor=meta.cursor, and the q+operator_id combination silently switches from name search to live rate-description search. It doesn't mention result ordering or rate limits, so not a 5.

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 dense sentences, front-loaded with purpose, then the anti-pattern with named alternatives, then the mode switch, then pagination. No filler and each sentence changes how the agent would call the tool.

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 an output schema exists, the description needn't document returns, and it covers the two things most likely to cause a bad call: picking this tool for top-ups and mishandling the q+operator_id mode. Minor gap: it doesn't clarify whether service_type or lang still apply in rate-description mode, leaving some parameter interaction to inference.

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 86%, so the baseline is 3; the description earns above that by explaining the non-obvious interaction where q changes meaning when operator_id is present (catalog names vs bundle/data descriptions) and by tying cursor to meta.cursor. Other parameters (limit, lang, service_type) are left entirely to 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?

States a specific verb and resource ('Browse the country catalog by operator/brand name') and scopes the content types (gift cards, gaming). It also explicitly separates itself from the mobile top-up flow, so an agent can distinguish it from get_operators, get_operator_rates and the esim siblings without opening a schema.

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?

Names the exclusions and the alternatives in sequence: for phone-number top-ups use lookup_carrier, then get_operator_service_types and get_operator_rates, 'NOT this tool alone'. It also explains the alternate search mode (operator_id + q) so the agent knows which invocation path to pick.

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