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

Annotations already declare readOnlyHint=false, destructiveHint=false, idempotentHint=false and openWorldHint=false, so safety is covered. The description usefully discloses that ancillary fields are optional, but it omits the critical behavior for a non-idempotent create: what happens when the email already exists, and what identifier is returned. That is a meaningful gap beyond the annotation baseline.

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 with the core action first and the optional extras after; no filler and every clause carries information.

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 create tool with a nested custom_fields object, no output schema and a non-idempotent annotation, the description should say what a successful call returns and how existing-email collisions are handled. It covers the field surface adequately but leaves the agent guessing on outcomes.

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 only 38%, so the description must compensate; it names four of eight parameters (audiences, custom_fields, tags, score) and clarifies they are optional. It says nothing about email being required, nor about first_name/last_name/unsubscribed, so partial compensation only.

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 a contact') and clarifies that audience subscription, custom fields, tags and lead score are bundled optional capabilities. That distinguishes it from narrower siblings like add-contact-tags or add-audience-subscriber, though it never names those alternatives.

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 phrase 'optionally subscribing it to audiences and setting custom fields, tags and a lead score' implies this is the one-shot creation path versus follow-up calls to the tag/audience tools. However there is no explicit when-to-use guidance, no mention of update-contact for existing records, and no stated precondition.

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