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 context beyond that by disclosing the GET /contacts endpoint and flagging the non-obvious inclusion of the Rinkel system contact (tag 'system'), which an agent might otherwise mistake for user data. It stops short of stating pagination/ordering behavior, so not a 5.

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 compact sentences with no filler: scope first, returned fields second, endpoint as a trailing hint. Nothing an agent does not need.

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 paginated list with no output schema, the description names the fields returned and the notable system-contact inclusion, and the schema carries paging details. Only minor gaps remain (total count, result ordering), which are unlikely to affect correct invocation.

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 description coverage is 100% and all four parameters (page, filter, letter, per_page) are documented with defaults and bounds in the schema. The description adds no extra meaning about filtering or letter semantics, 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?

A specific verb (List) plus a precisely scoped resource: contacts shared with everyone in the account, with the system contact called out explicitly. The list of returned fields (names, company, phone numbers, email) further pins down what an agent gets, and the scope wording separates it from get_contact, find_contact_by_number, and create_contact.

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 scope phrase 'shared with everyone in the account' implies this is the browse/enumerate operation rather than a targeted lookup, but the description never names alternatives such as rinkel_find_contact_by_number or rinkel_get_contact, nor states when not to use it. Usage is inferable, not stated.

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