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

Annotations only give a title and destructiveHint=true, so the description adds real value: it labels the operation WRITE, describes the precondition and the fact the session becomes unpayable. It could go further on irreversibility (whether an expired session can be reopened) and response shape, but the core behavior is disclosed.

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 compact sentences plus the endpoint, with the WRITE prefix and the key precondition front-loaded. No filler or redundancy.

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 two-parameter mutation with no output schema, the description covers purpose, precondition, and failure mode. A note on what happens to the customer after expiry (e.g., whether the session can be recreated) would make it fully 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 coverage is 100%, with session_id and idempotency_key fully documented in the schema, so the description carries no additional parameter burden. The description adds no syntax or format detail beyond what the schema already provides — baseline 3.

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 the exact verb and resource ('expire an OPEN Checkout Session'), the precondition (must be open), and the effect on the customer, plus the underlying endpoint. It is clearly distinguishable from qashier_get_checkout_session and qashier_create_checkout_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?

Explicitly scopes usage to sessions that are OPEN and states the failure condition when the session is not open, which is a clear usage context. It does not name alternatives (e.g., cancel vs refund) or exclusions, so it falls short of a 5.

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