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

Annotations already declare readOnlyHint=true, so safety is covered. The description adds useful behavioral context beyond that: the authentication requirement (API V3 token) and the underlying endpoint GET /v3/companies/{cif}/clients/{id}. It stops short of discussing permissions or error behavior.

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?

Two tight sentences: identity/return payload first, then the auth and endpoint detail. No filler, every clause earns its place.

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 single-parameter read tool, the description lists the returned fields (name, CIF, address, bank, contact, VAT flag, delivery addresses), states the auth requirement, and provides the endpoint. Nothing an agent needs to invoke it correctly is missing, even without an output schema.

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% and the single id parameter is documented in the schema with its pattern and 'from the list tool' hint, so the description's mention of the cus_ format is largely redundant. Baseline 3 applies when the schema carries the semantics.

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+resource ('One client by V3 id') and enumerates the returned fields, making it clearly distinguishable from the sibling list_clients and get_supplier tools.

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?

Notes the id comes 'from the list tool', implying the list-then-fetch workflow, and states the API V3 token requirement. It does not explicitly contrast with list_clients or state when-not to use it, but the routing context is clear.

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