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

Annotations already declare readOnlyHint=true, so the safety profile is covered. The description adds genuinely new behavioral context beyond that: the data is non-fiscal ('contix does not derive anything fiscal from it') and the return shape is a comma-separated list of names, which tells the agent not to expect structured objects or ids.

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 sentences, front-loaded with the verb and resource, then the domain definition, then the return format. The Spanish parenthetical earns its place given the tool's locale, though the 'Pure data / no fiscal derivation' clause is slightly defensive verbosity.

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?

For a zero-parameter read tool with no output schema, the description supplies the one thing missing from structured data: what the returned names look like (comma separated) and what the concept means. Only the absence of guidance on the write-side sibling keeps it from a 5.

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 tool takes zero parameters, so there is nothing for the description to disambiguate; baseline 4 applies. The description correctly implies no filtering or pagination options exist.

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 and resource ('List the account's product groups') and then defines the domain concept (an optional axis 'what was sold' that an invoice can carry) plus the Spanish term, which is the actual field name in the product. An agent knows exactly what this returns and how it differs from the mutating sibling set_product_groups.

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 verb — read the current catalogue of product groups — but there is no explicit routing such as 'to change them, use set_product_groups' or a note on when an agent should consult this list before creating an invoice. Adequate, not instructive.

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