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

Annotations only supply destructiveHint=true; the description adds the far more actionable detail that any custom field NOT passed is reset, which explains why the operation is destructive. That is exactly the kind of hidden side effect an agent needs before calling.

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 tight sentences with the key risk (field reset) front-loaded ahead of the alternative tool and endpoint. The trailing 'HappyFox: POST /api/1.1/json/users/' adds little for an agent and is the only mildly wasteful element.

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 4-parameter create tool with no output schema and annotations covering only destructiveness, the description supplies the identity key, the destructive side effect, and the routing alternative. Nothing needed to invoke it correctly is missing.

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%, so the baseline is 3, but the description adds meaning beyond the schema: email acts as the identity key for the upsert, and the reset behavior governs how custom_fields must be populated. The custom_fields entry-format detail lives in the schema, so this is additive rather than redundant.

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 clarifies the non-obvious upsert semantics keyed on email. It also names the sibling it should not be confused with (happyfox_update_contact), so an agent can separate the two without opening either schema.

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?

It explicitly names the alternative ('use happyfox_update_contact to edit an existing contact') and explains the email-keyed create-or-edit condition. The guidance is slightly self-inconsistent, since the tool itself updates existing contacts, leaving some ambiguity about when update_contact is genuinely preferred over this call.

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