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

readOnlyHint=true already establishes the safe-read profile, so the bar is lower, and the description adds real behavioral detail beyond it: pagination, the searchable fields, the phone 'digits only, no +' constraint, and the 'space-separated, all must match' matching semantics. It does not disclose the response shape, but the search behavior is genuinely useful.

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?

The description is dense but front-loaded, leading with what the tool does before the search-field detail and the underlying API endpoint. Every clause carries information; the only slightly extraneous element is the trailing endpoint reference.

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 list/search tool with no output schema, the description supplies the two things an agent most needs — pagination behavior and the syntax/semantics of the search query, including a worked example. Combined with readOnlyHint annotations, an agent has enough to call it correctly.

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 the baseline would be 3, but the description enriches `q` well beyond the schema by enumerating the searchable fields (name, email, phone, updated_since, created_since), giving a concrete example, and stating the AND-matching rule and phone format. This adds meaning the schema's generic 'field:value pairs' string does not convey.

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?

The description opens with a specific verb+resource ('List contacts (customers), paginated, or search them'), making the list/search batch nature clear and implicitly distinct from the singular get_contact sibling. It stops short of explicitly naming that sibling, so the differentiation is inherent rather than stated.

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: the tool lists or searches, and the field list tells the agent what can be searched. However, there is no explicit when-to-use guidance — e.g., when to reach for this versus happyfox_get_contact for a single record, or how it relates to list_contact_groups.

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