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

Annotations already declare readOnlyHint=false, destructiveHint=false and closed-world scope, so the agent knows this is a non-destructive write. The description adds nothing beyond that: it doesn't say what happens on duplicate enrollment, whether the call is idempotent, or that the contact begins receiving automated emails/messages as a side effect — the key behavioral consequence of a mutation like this.

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 no filler, and the two required lookups are surfaced before any detail. Slightly dense with the parenthetical qualifier, but nothing is wasted.

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?

An output schema exists so return values need not be explained, and all parameters are documented. What's missing for a mutation tool is behavioral completeness: preconditions on the contact, duplicate/already-enrolled behavior, and any permission or rate considerations.

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 all four parameters (including the id sources and the case-insensitive name match) are already documented in the schema; the description largely restates them. Baseline 3 applies — it adds no format, precedence, or conflict-resolution rules (e.g., what if both contact_id and email are supplied).

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+resource: start/enroll a contact in an automation, with the two identifier paths spelled out. It references list_automations as the name source, which partly orients it among siblings, but never distinguishes itself from adjacent tools like upsert_contact or send_email for the 'contact may not exist yet' case.

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?

Operational context is decent: it names the id sources (automation_id or automation_name, contact_id or email) and where names come from. However there is no statement of prerequisites (must the contact already exist?), no when-not guidance, and no explicit alternative named for the 'create the contact first' scenario.

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