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

Annotations already establish this is a mutating, non-idempotent, non-destructive operation. The description adds meaningful context: updating triggers re-pricing and returns the same session object as create_checkout. It does not contradict the annotations.

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 tight sentences with no filler; the mutating action and key consequences, re-pricing and same return shape, are front-loaded. Every clause adds 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?

The description covers the core scenario and return behavior, with the output schema filling in return details. Missing pieces include partial-update semantics, the required session ID, and when to use sibling checkout tools, so it is adequate but not complete.

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 0%, so the description must compensate, but it only restates the top-level fields (items, state, buyer) and never explains checkout_session_id or parameter semantics. It offers little help beyond property names, only clarifying that 'buyer' refers to buyer details.

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?

Description uses a specific verb ('Change') with a clear resource ('open checkout session') and enumerates the mutable parts: items, state, and buyer details. It also adds re-pricing behavior and distinguishes itself from create_checkout by noting the returned object is the same session.

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 implies an existing, open session is the target, but it never names create_checkout for new sessions or complete_checkout for finalizing one. The only sibling mention is about return shape, not routing, so the agent must infer when to use this over alternatives.

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