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

Annotations already declare the safety profile (readOnly=false, destructiveHint=false, idempotentHint=false), and the description adds genuinely useful context beyond them: the bill history is retained, autopay is terminated as a side effect, and the bill is removed from expectations. It doesn't cover reversibility or failure behavior, but it clears the bar set by the existing 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?

Front-loaded and short, with the gating condition early. Minor redundancy: 'Autopay ends with it' is restated in 'Effects: … autopay ended', slightly denting efficiency but not readability.

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 tool with full annotations and no output schema, the description supplies the essential facts: retained history, autopay termination, and the precondition. Only irreversibility/reinstatement and permission requirements are left unstated.

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 two required parameters, and the schema already documents series_id format and reason. The description only echoes 'with a reason' and adds nothing about the series_id or what a valid reason looks like, so baseline 3 applies.

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 action – ending the expectation of a recurring vendor bill series – and the parenthetical '(moved, cancelled, switched provider)' plus 'Its bills stay on record' make the effect explicit. It is distinguishable from siblings like purch_declare_bill_series or purch_cancel_subscription by focus on the expectation, though it never names those alternatives.

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?

'Only when the person says the bill has stopped' gives a clear gating condition for use, which is more than most tools offer. However, there is no explicit routing away from near-neighbours such as purch_declare_bill_series, purch_cancel_subscription, or purch_end_rule, so the agent must infer when this is preferred.

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