check_qr_url

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

Annotations already declare readOnlyHint, idempotentHint and openWorldHint=false, so the safety profile is covered. The description adds real value by listing the four validation dimensions (host, path, parameters, formats) and stating there is no cost, but it does not say what happens when the URL fails a check or whether validation is against a live AEAT service.

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?

One front-loaded sentence covering domain, validation scope and cost, with no filler. The trailing 'Free.' is terse but earns its place as a cost signal.

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?

An output schema exists, so return values need not be explained, and the tool is simple with one parameter. Still missing is any failure-mode hint or sibling routing, which matters given a near-identical QR sibling in the toolset.

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?

The single 'url' parameter has 0% schema description coverage, so the description must compensate. Specifying 'a tax QR URL read from an invoice' narrows the expected input domain, which helps, but it gives no format or shape hints for the string itself.

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 ('Check') and a precise resource ('a tax QR URL read from an invoice'), and enumerates what is validated: official AEAT host, path, parameters and formats. It does not name the obvious sibling generate_verifactu_qr, so the check-vs-generate distinction is left to inference.

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?

'read from an invoice' implies the input context, and 'Free' signals no credit cost, but there is no explicit when-to-use framing, no exclusions, and no pointer to generate_verifactu_qr when the agent needs to produce a QR rather than inspect one.

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