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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), so the description is free to add value — and it does, disclosing the return shape: a likely service, a small candidate set with check-locations for Apple/Amazon/Google/Microsoft, or a match:purchase classification for one-off orders. This output variability is exactly the kind of context annotations cannot convey.

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?

The two opening fragments ("Cancel My Sub. Which subscription is this charge?.") merely restate the tool name and title and earn no place. The remainder is information-dense, but the "Returns..." sentence is a run-on that mixes several output cases in one breath.

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-parameter tool with no output schema, the description covers the need: what to pass, what comes back, and the mandated follow-up call. Only minor gaps remain, such as what happens for a charge that matches no known service.

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 a single parameter at 100% schema coverage the baseline is 3, but the description goes further by supplying real-world example values (statement-form merchant strings) that illustrate the expected input format beyond the schema's "The charge as it appears on the statement" note.

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 action (identify which subscription a statement charge belongs to) with concrete example inputs like "APPLE.COM/BILL" and "DD *DOORDASH DASHPASS". It is clearly distinguishable from siblings such as list_services and get_cancel_steps, and it explicitly hands off to getCancelSteps as the follow-up.

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?

"Use for ..." plus three representative charge strings gives a clear triggering context, and the closing "Then call getCancelSteps" establishes the sequencing with a sibling. It stops short of stating when NOT to use it or pointing to list_services as an alternative for browsing known services.

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