Rent an extension

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

The description discloses that the tool deducts from a separate balance (USSD balance) and requires a scope, which adds behavioral context beyond the annotations (readOnlyHint=false, destructiveHint=false). However, it does not cover other aspects like failure behavior, rate limits, or idempotency, which are still unclear.

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?

The description is two sentences, each sentence adds unique value: first states the balance deduction, second states the action and pricing. No redundancy, front-loaded key 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?

Given the tool has 3 parameters, no output schema, and moderate annotation coverage, the description covers purpose, financial implication, pricing logic, and scope requirement. It lacks mention of prerequisite steps (e.g., checking availability) but is still fairly complete for a simple rental operation.

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?

With 100% schema description coverage, the schema already documents parameters (code, app_id, short_code). The description adds general context (e.g., numeric extension, shared short code) but does not provide specific parameter-level guidance beyond what is in 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 clearly states it deducts from USSD balance and rents a numeric extension on a shared short code, with pricing by digit length. This distinguishes it from sibling tools like hellio_ussd_check_extension_availability, hellio_ussd_list_extensions, and hellio_ussd_release_extension because it explicitly uses the verb 'rents' and mentions the financial transaction.

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 description provides context on when to use: it requires the 'ussd' scope and explains pricing implications (shorter digits are premium). It does not explicitly state when not to use or directly compare with alternatives, but the context is clear enough for an agent to understand prerequisites and cost considerations.

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