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

readOnlyHint=true already declares the operation safe and non-mutating, so the description is not obligated to cover that. It does add useful behavioral context by enumerating the returned payload (including refunds), which matters because no output schema exists; it stops short of describing not-found or expired-session behavior.

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 sentence that front-loads the verb and resource, then lists the returned fields, with the HTTP endpoint tacked on as compact supplementary context. Nothing is redundant.

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 one-param read tool with no output schema, enumerating the return fields is the key missing piece and it is present. The remaining gap is error/absence semantics (not found, expired), which is minor here given readOnlyHint and the trivially simple schema.

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?

With one parameter at 100% schema coverage, the schema already defines session_id with a minLength constraint. The description's 'by id' and the '/checkout/sessions/{id}' path reinforce where the id goes but add no format or sourcing detail beyond the schema.

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 ('Get one Checkout Session by id') and enumerates the fields it surfaces (status, payment status, payment method, amount, checkout url, refunds). The singular 'one ... by id' framing clearly separates it from qashier_list_checkout_sessions without needing to name the sibling.

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?

Usage is only implied: an agent infers it should call this when it already holds a session_id. There is no explicit guidance on when to prefer list_checkout_sessions or expire_checkout_session, nor any note about what to do if the session is missing or expired.

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