Add or update contact

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

Annotations declare readOnlyHint=false, destructiveHint=false, and openWorldHint=true, so the safety profile is partly covered. The description adds useful behavior (custom fields keyed by tag, add/remove tags, status) but does not say whether an update overwrites or preserves omitted fields/tags, which matters for a non-destructive-flagged upsert.

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?

A single, front-loaded sentence that leads with the core create-or-update behavior. It is efficient with no wasted clauses, though it tries to pack three capabilities into one line.

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 6-param mutation tool with no output schema, the description is adequate but thin: it omits the upsert-vs-update_contact routing decision and the overwrite semantics of updating 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 50%. The description explains that fields are set by tag, and mentions add/remove tags and status, adding meaning beyond the bare schema for those params. It does not address listId or email_address, though those are required and relatively self-evident.

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 verb and resource and clearly captures the upsert semantics ('Create a contact, or update it if the email already exists in the list'). However, it never distinguishes this from the sibling update_contact, so an agent can't tell from the description alone which one applies.

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?

There is no when-to-use or when-not-to-use guidance. With a sibling named update_contact that also mutates contacts, the choice between the two is left entirely to inference, which is a meaningful gap.

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