Add a contact

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

Annotations already declare it is a write (readOnlyHint=false), not idempotent, non-destructive, and open-world. The description adds real behavioral context beyond that: the default target is the signed-in mailbox's own address book, and choosing a shared mailbox makes the contact visible to everyone with access, including via CardDAV. It stops short of covering permission requirements or what happens if a duplicate is still created.

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?

Two sentences, both front-loaded with the action and the constraint; no filler, no repetition of the title. The scoping detail about shared-mailbox visibility is placed exactly where the account decision is made.

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 11-parameter, zero-required mutation tool with no output schema, the description covers the destination and the dedupe prerequisite well. Minor gaps remain: it does not state the minimum viable contact (all fields optional — can an empty contact be created?), nor what the tool returns or whether duplicates are rejected server-side.

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. The description restates the account default/shared semantics that the schema's 'account' description already covers in more detail, and adds no new field-level information (requiredness, email format, or address_book behavior) beyond the 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?

States a specific verb and resource ('Creates a contact in an address book') and immediately scopes the default destination, which distinguishes it from the read-only sibling mail_search_contacts. An agent can tell what this tool does and what it does not do 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?

Explicitly names the alternative ('Check mail_search_contacts first so you do not create a duplicate') and gives the selection rule for the account parameter (empty for the signed-in mailbox, shared mailbox name otherwise). Both the duplicate-avoidance workflow and the destination choice are spelled out rather than inferred.

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