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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, but the description adds real beyond-schema facts: format only and it never claims a payment, deterministic output for identical input, no network or stored state, and concrete limits (64 KB input, 1 s per call, 1 MB result). Only the read-only/no-side-effect restatement is redundant with the 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?

Front-loaded with the core verb statement, but it pads with a mismatched 'Cuándo' sentence about rounding/rates, then repeats the whole definition as a truncated EN block ending in a meta-reference '[EN completo / full EN: inputSchema.description]'. Those notches cost space without adding decision value.

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 12 optional parameters, an output schema, and full annotation coverage, the definition still supplies what matters: build-vs-parse mode via action, key-or-URL choice, no-payment guarantee, determinism, and hard size/time limits. Nothing an agent needs to invoke it correctly is missing.

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 100%, so the baseline is 3. The description does add the useful semantic point that key and dynamic URL are alternatives ('llave o URL dinámica'), but the schema already says 'instead of key' on url, so marginal value is small.

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 pair and resource: builds a Pix BR Code (EMVCo TLV with GUI br.gov.bcb.pix, key or dynamic URL, amount, txid, CRC16) or parses/checks one, per Banco Central do Brasil manuals. It explicitly names the sibling it is not for (emvco-qr-parse), so an agent can discriminate without opening a 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?

'No para: leer un payload QR EMVCo de comercio (emvco-qr-parse)' gives an explicit exclusion plus the alternative tool, which is the strongest part. The positive 'Cuándo' clause, however, talks about money/tax/financial-math exactness, which reads as boilerplate from a math toolkit and does not actually describe the Pix-BR-Code use case.

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