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

Annotations already declare destructiveHint=true, idempotentHint=true, and readOnlyHint=false, so the mutation semantics are covered by structured data. The description contributes one genuinely new behavioral fact — the required OAuth scope — but says nothing about whether the update is partial or full, what happens to omitted fields, or irreversible side effects (e.g. voiding an invoice).

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 short sentences, front-loaded with the action and followed by the precondition; no filler, no repetition of the title or parameter names.

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 15-parameter mutation tool with no output schema, the description is thin: it never suggests which fields are updatable, whether some fields (e.g. status transitions to 'paid') carry side effects, or what the caller should expect back. Annotations carry the safety profile, but the description leaves meaningful operational questions open.

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% across all 15 parameters, so the schema already documents every field including the enum values for status. The description's 'by ID' is the only parameter-related content and adds nothing the schema does not already state, 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 and resource and adds a concrete scope qualifier ('existing invoice by ID'), which tells an agent this is an in-place update rather than a create or delete. It does not name or differentiate itself from siblings like bulk_update or update_work_order, but the verb+resource pairing is 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?

The only guidance is the permission prerequisite ('Requires invoices:write scope'), which is a condition for calling, not a when-to-use/when-not-to-use statement. There is no mention of alternatives such as bulk_update or of when to prefer this over recreating an invoice.

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