create_contact

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

Annotations already flag readOnlyHint=false, destructiveHint=true, openWorldHint=true, and the description adds real context the annotations don't: the operation is an upsert (so it can modify existing data, not just insert), it is one-way, and changes do not propagate to native macOS/iOS Contacts. That non-obvious side effect is exactly the kind of disclosure the agent needs; what's missing is what an upsert collision overwrites and whether any auth/confirmation is required.

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 short sentences, front-loaded with the verb and action, then the trigger, then the constraint, then the caveat. Nothing is redundant; every sentence carries information the agent would otherwise lack.

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 mutation with no output schema and annotations covering the safety profile, the description supplies the trigger, the minimum-data rule, and the sync caveat. The remaining gap is what the call returns and how upsert matching/overwrite behaves, which an agent would need to proceed confidently on an existing contact.

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 per-field meanings are already handled, and the description still contributes a cross-field constraint ('at least one of phone_number or email') that the schema does not express — required is empty and there is no anyOf. It does not explain how the upsert matches an existing contact (by phone, email, or name), which leaves the most important parameter interaction unstated.

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 and resource ('Create or upsert a contact') and immediately clarifies the colloquial trigger ('save' a new person). It is distinguishable from list_contacts and find_contact by implication (writing vs reading), but never names or contrasts those siblings explicitly.

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?

'Use when the user asks to "save" a new person to their address book' gives a concrete usage trigger, and 'Requires at least one of phone_number or email' states a precondition. It stops short of saying when NOT to use it or how it relates to find_contact/list_contacts, so no exclusion or alternative is offered.

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