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

Annotations (readOnlyHint=false, destructiveHint=false) already establish that this is a write operation. The description adds the useful nuance that only firstName is required and other details can be deferred, but it doesn't mention potential side effects like duplicate creation, validation constraints, or how the household is selected.

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 two sentences: the first states the primary purpose, the second clarifies required vs optional fields and mentions the update path. No redundant information, perfectly front-loaded and easy to parse.

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 9 parameters, nested objects, and an output schema, the description provides sufficient context: it clarifies the creation action, the minimal required field, and the ability to update later. The rich schema and output schema cover details like property formats and return values. A minor gap is not explaining which household is targeted, but that's likely implicit.

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% with descriptive property definitions, so baseline is 3. The description adds value beyond the schema's `required` array by stating that all other fields are optional and can be filled later, which clarifies the intended workflow and reduces the agent's uncertainty about which parameters to provide.

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 clearly states 'Create a contact in the household's address book' – a specific verb and resource. It distinguishes itself from sibling tools like update_contact, delete_contact, and list_contacts by focusing on the creation action and noting that optional fields can be filled later with update_contact.

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 update_contact as the alternative for filling in optional details later, providing clear context for when to use this tool. However, it lacks explicit 'when not to use' conditions, such as if a contact already exists and should be updated instead.

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