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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false, and openWorldHint=false, so the safety profile is covered. The description adds the meaningful qualification 'structurally' and 'length', signalling that this is a format/length check rather than authenticity or check-digit verification — but it never states what a result looks like or what failure means, and there is no output schema to fall back on.

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?

A single, front-loaded sentence with no filler; the scoping qualifier 'structurally' appears before the resource, so the most decision-relevant information arrives first.

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?

The tool is simple (two required scalars, no nesting), but with no output schema the description should say what a successful or failed validation returns, and it should point at list_banks for valid bank codes. Those two omissions are the main gaps for an otherwise small, well-bounded tool.

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 0%, so the description must carry the burden. It does add that bank_code is a Bank Indonesia code and that account_number is checked for length, but it does not explain where bank_code values come from (e.g., list_banks), whether codes are numeric or prefixed, or what account_number format is expected, leaving real ambiguity.

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 names a specific verb ('validate'), a specific resource ('bank account number length'), and a required input qualifier ('for a given BI bank code'), which cleanly separates it from the other validators in the sibling list (validate_nik, validate_npwp, validate_phone). An agent can decide relevance without opening the 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?

It gives no explicit when-to-use or when-not-to-use guidance, and does not mention the obvious prerequisite/prerequisite-tool relationship with list_banks for obtaining a valid bank_code. Usage is only implied by the tool name and the word 'validate'.

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