sepa_creditor_id

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

Annotations already declare readOnlyHint, idempotentHint and openWorldHint=false, so safety is covered. The description adds genuinely new context: the output is deterministic and derived per EPC262-08, and the call is free — a useful cost signal given the presence of pricing/credits_balance siblings. It omits error behavior for an invalid NIF.

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?

Three short, front-loaded lines: purpose, output format, and downstream use. Nothing is redundant, and the format specification is compactly encoded in a single template string.

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?

With an output schema and rich annotations already present, the description supplies the remaining essentials: what is produced, per which standard, and why. It could be stronger by specifying accepted NIF formats and what happens on an invalid input, but it is sufficient to invoke correctly.

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 carry the load, and it does partly: it explains the business_code as a 3-character code defaulting to '000', which the bare schema does not. The NIF parameter's expected format is left unstated, which is the main residual gap.

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?

States a specific verb ('Compute') and a precise resource ('Spanish SEPA creditor identifier (AT-02)') derived from a named input ('from a NIF'). This clearly separates it from siblings like validate_identifier (which checks rather than generates) and parse_norma43.

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?

Gives a concrete application context: needed to issue SEPA direct debits (adeudos/remesas de recibos, Cuaderno 19.14). It does not, however, explicitly state when-not to use it or point to an alternative sibling such as validate_identifier for checking an existing ID.

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