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

Annotations only say readOnly=false, destructive=false, idempotent=true; the description goes materially beyond them by asserting the write is progress-bookkeeping only and has no external side effects on payment, plans, or numbers. That is exactly the disambiguation an agent needs before committing a state change during checkout.

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, no filler, with the core action stated first and the side-effect disclaimer second. Every clause earns its place by either defining the action or blocking a misread.

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?

With only two enum parameters, an output schema present, and annotations covering the safety profile, the remaining need is to prevent conflating a progress write with an actual checkout action — which the description does explicitly. Nothing an agent needs in order to call this correctly is absent.

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 0%, so the description carries the load, and it does enumerate the meaningful values: inbound/outbound intent and checkout/complete/skipped status. It stops short of explaining what 'both' means for intent or why 'checkout' is a distinct state, leaving the enum semantics partly implicit.

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 names a specific verb and resource ('Save only setup progress') and immediately scopes it to the two fields being persisted (intent, checklist status). It also draws a bright line against the payment/number-acquisition siblings, so an agent can distinguish it from claim_phone_number or create_billing_portal without opening any 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?

It gives clear when-to-use ('choose intent and mark the checklist') and a strong when-not ('never opens payment, buys a plan or acquires a number'), which prevents the most likely misfire toward billing/phone-number tools. What's missing is a positive statement of where in the onboarding flow this belongs and whether it is safe to call repeatedly mid-flow.

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