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

Annotations only declare destructiveHint=true; the description supplies the crucial missing detail of WHAT is destroyed ('any contact custom field NOT passed is reset') and the create-or-edit keying on email. This is meaningful context beyond the annotation. It stops short of describing return values or auth/permission requirements, so not a full 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 dense sentences, front-loaded with the action and the critical reset warning. Every clause earns its place; nothing is repeated from the schema or annotations.

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 mutation tool with no output schema, the description covers the essential risk (custom fields reset), the alternative tool for editing, and the create-or-edit keying. Combined with rich schema coverage, an agent has everything needed 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 description coverage is 100% and the per-field descriptions (phones, custom_fields, enum meanings) are already thorough, so the schema carries the parameter burden. The description adds no per-parameter syntax or format beyond what the schema states, making the baseline 3 appropriate.

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 ('Create a contact') and immediately distinguishes itself from the sibling happyfox_update_contact by naming it. It also clarifies the surprising create-or-edit semantics up front, so an agent can tell exactly what this tool does versus its alternatives.

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?

Explicitly routes the agent: use this to create, and 'use happyfox_update_contact to edit an existing contact.' It also flags the edge case where an existing email triggers an update, which is precisely when an agent might otherwise pick the wrong tool.

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