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

readOnlyHint=true already tells the agent this is a safe read. The description contributes the return field set and the underlying GET path, which is useful, but says nothing about pagination, result size, or whether an unknown CIF errors or returns empty.

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 compact sentence with the resource and return fields front-loaded, followed by the endpoint. No filler, though the trailing HTTP path is marginal value for an agent that only needs the tool contract.

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?

There is no output schema, so the parenthetical field list is the only disclosure of return shape and it is included. For a trivial one-parameter read tool this is close to sufficient; only error/empty behavior is unaddressed.

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 100%: the single cif parameter is fully documented in the schema, including a pointer to oblio_list_companies and a concrete example. The description adds nothing about the parameter, so the baseline 3 applies.

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?

Names a specific resource (VAT rates) and enumerates the salient returned fields (name, percent, default), so the agent knows exactly what comes back. It doesn't explicitly contrast with a sibling, but the resource is unambiguous within the oblio_list_* family.

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?

"use the name and percent on document lines" gives implied usage context — you fetch these to populate document lines — but there is no statement of when to call this versus another lookup, nor any prerequisite or exclusion beyond the CIF requirement.

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