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

readOnlyHint=true already establishes the read-only safety profile. The description adds real behavioral context beyond annotations: paginated retrieval, the searchable field set, the digit-only phone format, and the underlying endpoint (GET /api/1.1/json/users/).

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?

Front-loaded with the action and resource, then search syntax, then endpoint. Two compact sentences with no filler. Slightly dense but every clause adds usable detail.

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 3-param list/search tool with annotations present and no output schema, the description covers search semantics, pagination, and the backing endpoint. It stops short of describing return shape or pagination totals, but that is a minor gap given coverage elsewhere.

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 baseline is 3. The description goes further by enumerating the valid `q` fields (name, email, phone, updated_since, created_since), the digit-only phone constraint, space-separated AND semantics, and an example — none of which the schema's 'field:value pairs' description provides.

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 states a specific verb pair (list/search) and resource (contacts, clarified as customers), plus pagination. It's clear what the tool does, though it does not explicitly name a sibling (e.g. get_contact) to differentiate the single-record vs list case.

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: list paginated or search by field. But there is no explicit when-to-use narrative contrasting it with happyfox_get_contact or happyfox_list_contact_groups, so the agent must infer the selection context.

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