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 value by disclosing the returned payload (phones, contact groups, ticket counts, custom fields) and the underlying API endpoint. It stops short of noting auth requirements, rate limits, or error behavior for an unknown id/email.

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?

One sentence plus the API path; the lookup behaviour and returned fields are front-loaded and nothing is wasted.

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?

With no output schema, the enumeration of returned fields usefully compensates, and read-only behaviour is covered by annotations. A brief note on ambiguous or missing lookup keys would make it fully complete.

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% and the single 'contact' parameter is already documented with its id/email formats. The description restates the same id-or-email duality without adding syntax, format, or edge-case detail beyond the schema, 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?

States a specific verb ('Fetch') and resource ('a contact') plus the two lookup keys (id or email) and enumerates what the response contains. An agent can distinguish this from happyfox_list_contacts or happyfox_get_contact_group without opening the 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?

Implicit usage is conveyed by 'by id or by email address', and the sibling list makes the single-vs-list distinction inferable, but the description never explicitly says when to prefer this over happyfox_list_contacts or happyfox_update_contact, nor does it state any prerequisites.

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