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

The annotations already cover read-only, idempotent and open-world behavior. The description adds context beyond them: the tool performs an operator-detection step against live data, and it describes the payload fields (what the recipient receives, validity, USD price) and the input-format precondition.

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?

It leads with the purpose ("Mobile recharge..."), pauses only to list the returned item types, and ends with the format requirement and an example. Every clause adds information, and no sentence is redundant.

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 one-parameter read tool with annotations but no output schema, it adequately describes both what goes in and what comes back. Minor gaps: it says nothing about behavior when operator detection fails or about whether prices are always in USD for non-US numbers.

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 the one parameter is already documented, which sets the baseline at 3. The description earns a 4 by adding a concrete format example (+911234567890) and explaining why the country code matters: operator detection depends on it.

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 states a specific verb and resource: it detects the carrier for a phone number and returns live recharge/top-up options, broken down into airtime, data packs and plans. It implies the difference from get_esim_plans (mobile recharge versus eSIM), but never names that sibling explicitly.

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 text says what the tool does, so the use case is implied: get recharge options for a given number. It does not say when to choose this over get_esim_plans, check_phone_compatibility or check_esim_status, and it never states when not to use it, such as for landlines or numbers without a carrier.

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