validate_identifier

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

Annotations already establish readOnly, idempotent and closed-world, so the bar is lower; the description still adds real behavior: the ES inner CCC check, automatic kind detection, and the fact that failures return the expected control digits rather than erroring out. It also flags 'Free', which matters given a pricing/credits_balance sibling set. Minor gap: no statement about input length limits or non-identifier inputs.

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?

Front-loaded with purpose, then supported kinds, then return behavior, then args — a sensible order with no filler sentences. The backtick-marked tokens and 'Args:' block are slightly markdown-heavy for the amount of content, but nothing 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?

Output schema exists so return values need not be explained, yet the description still summarizes them usefully. For a two-parameter pure-validation tool, the only real omission is behavior on unrecognizable input (return invalid vs. raise), which the 'when wrong, expected control digits' phrasing only partly resolves.

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% and the schema has no enum for `kind`, so the description carries the full burden and does: it gives the accepted `kind` values (auto | iban | ccc | nif | creditor_id | reference1) and states that `value` tolerates spaces and dashes. This is meaning the agent cannot get from 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?

Opens with a specific verb+resource ('Validate a Spanish/EU banking identifier') and enumerates exactly which identifier families are covered (IBAN/SEPA, CCC, NIF/NIE/CIF, AT-02 creditor ID, Norma 43 Referencia 1). It does not explicitly differentiate itself from the sibling sepa_creditor_id, which is the one tool an agent could plausibly confuse it with.

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?

Usage is implied by the enumeration of supported formats and the 'Free' note, but there is no explicit statement of when to call this versus sepa_creditor_id or parse_norma43, nor any prerequisite or exclusion guidance.

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