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

The description discloses that the tool consumes saldo (a side effect) and is a UTIL service with a fee, which is beyond the annotations (readOnlyHint=false does not capture this). It also clarifies that it only validates structure, not existence, adding behavioral detail not present in annotations.

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 three sentences, each earning its place: purpose, cost/where to check, and limitation. It is front-loaded with the core action and has no redundant words.

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 single-parameter validation tool with an output schema, the description covers all necessary aspects: what it validates, the cost and where to check it, and a key limitation. The output schema handles return values, so no further explanation is needed.

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 0%, so the description must compensate. It explains the structural requirements of a CLABE (18 digits, control digit, bank prefix), which directly informs the expected format of the 'clabe' parameter. While it does not explicitly state 'clabe must be an 18-digit string', the description implies it sufficiently.

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 uses a specific verb ('Valida') and resource ('CLABE'), and enumerates exactly what is checked: 18 digits, control digit, and bank by prefix. It also explicitly states what it does NOT do (confirm account existence), which differentiates it from verification tools among the siblings.

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 clear context: it is a paid service (consumes saldo) and indicates where to check the fee (consultar_precios). It also states a limitation ('No confirma que la cuenta exista'), implying that if existence verification is needed, another tool should be used, though it does not name a specific alternative.

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