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

Annotations only flag destructiveHint=true; the description goes well beyond that by disclosing the exact consequences (invoice becomes immutable, number preserved, billable hours/expenses are released back to unbilled work), the blocking preconditions, and the preview-without-confirm behavior. This is precisely the behavioral context a mutation tool needs.

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-loads the core effect, then layers the draft exception, the blocking conditions, and the confirm requirement in tight, non-redundant sentences. Every clause earns its place; no filler.

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?

No output schema exists, and the description supplies all the operational essentials an agent needs: effects, forbidden states, and the confirmation gate. Nothing material is missing for calling this tool correctly.

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 description coverage is 100%, and the confirm parameter's preview-vs-action semantics are already fully documented in the schema. The description restates that confirm:true is required without adding syntax or format detail beyond the schema, so the 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?

States a specific verb (voids) and resource (sent invoice or estimate), then immediately enumerates the concrete effects (immutable, number kept, hours/expenses returned to unbilled work). It explicitly distinguishes itself from the draft path ('A draft is not voided (it is deleted)'), so an agent can tell it apart from delete_invoice_draft without opening either schema.

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?

Gives explicit when-not conditions: drafts go elsewhere (deleted), invoices with recorded payments cannot be voided, and estimates whose invoice still stands cannot be voided. It also states the confirm:true prerequisite for the real action versus a preview. Nothing about selecting this tool is left to inference.

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