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

Annotations already declare readOnlyHint=true, and the description is consistent with that. It adds real behavioral context beyond the annotations — normalisation of the input and an optional availability lookup — but does not say what happens on an invalid number (error vs. a validity flag) or what the response shape is beyond 'normalised form'.

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 with no waste; the core purpose is front-loaded and the optional flag and API endpoint follow in descending order of importance.

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 read-only validator with a fully described three-parameter schema and no output schema, the description covers purpose, the optional inventory mode, and the endpoint. Only the outcome when validation fails and the exact result fields are left implicit.

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%, so all three parameters are already documented in the schema, including 'number without the country calling code'. The description only echoes check_inventory's meaning and adds the notion of a normalised output, 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?

States a specific verb and resource — check/normalise a phone number for a given country — which is clearly distinct from rinkel_get_number (retrieve a stored number) and rinkel_find_contact_by_number. It does not explicitly name those siblings, but the operation is unambiguous from the sentence and name.

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?

The conditional 'With check_inventory=true Rinkel also checks whether the number is available to order' implies when to flip that flag, but there is no explicit when-to-use guidance versus siblings such as rinkel_get_number or rinkel_block_number, and no stated exclusions or prerequisites.

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