Create a contact

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

Annotations already signal a write operation (readOnlyHint=false) and non-idempotency (idempotentHint=false). The description adds concrete behavioral context beyond that: Google performs no duplicate check, so repeated calls create duplicate contacts, and 'at least one field is required' states an input constraint. This enriches what annotations alone provide.

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 terse sentences, each earning its place: the core action, the required-input constraint, and the duplicate warning. The most important information is front-loaded and there is no filler or repetition of schema content.

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 an 8-parameter write tool with no output schema, the description covers the key operational risks (duplicates, minimum fields) and the schema documents every parameter with 100% coverage. The only minor gap is that it does not address account context or the return value, but for a create action with no output schema this is acceptable.

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 the baseline is 3. The description adds one genuinely new semantic rule not derivable from the schema: despite only 'account' being formally required, at least one additional contact field must be supplied. This cross-parameter constraint adds value beyond the JSON Schema.

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 action and resource: 'Add a person to the account address book.' It also scopes the tool to the 'account' address book, which combined with the sibling names (contacts_search, contacts_get, contacts_list, contacts_update) clearly distinguishes creation from the other contact operations.

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?

The description gives explicit guidance: 'Google does not check for duplicates — search first if the person might already be there.' This tells the agent to consult search before creating, which is clear when-to-use context. It does not name the sibling tool (contacts_search) explicitly, but the directive is actionable and sufficient.

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