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

Annotations already declare destructiveHint=true, but description adds valuable behavioral detail: 'invoice can no longer be paid or edited; existing payments are preserved as history.' This goes beyond the annotation by explaining what destruction entails. No contradiction with 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?

Three sentences, each earning its place: first states action, second explains consequences, third lists restriction. No redundant words. Front-loaded with the primary purpose.

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?

Tool is simple (one parameter, no nesting). Description covers behavior, consequences, and constraint. Output schema exists (though not shown), so no need to explain return values. Fully adequate for effective use.

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?

Only one parameter 'invoiceId' with schema description 'Invoice ID to void.' Schema coverage is 100%, so the description adds no additional meaning beyond what the schema already provides. Baseline score of 3 is appropriate.

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 clearly states the action ('Void an invoice'), identifies the resource, and explains the consequences (no longer paid/edited, payments preserved). It implicitly distinguishes from siblings like 'delete_invoice' by noting preservation of payments. The verb+resource+scope is specific and unambiguous.

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?

Includes explicit precondition ('Cannot void invoices that are already PAID or VOIDED'), guiding when not to use. Does not directly compare to alternatives like 'delete_invoice' or 'mark_invoice_sent', but the destructive nature and constraint provide clear usage context.

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