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

Annotations only provide readOnly=false, idempotent=false, destructive=false, so the description adds the key behavior: it returns a draft that can still be revised, and credit_note_finalize later burns the final CN number. This is the most important non-obvious behavior, though it does not discuss duplicate handling or side effects beyond the draft state.

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 dense sentences: the first scopes the operation and enumerates key fields, the second explains the draft workflow and the finalize step. No filler or repetition.

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 9-parameter creation tool with no output schema, the description covers the core workflow: create draft, revise later, finalize later. It does not describe the draft response shape, but 'returns a draft' plus the fully documented schema is adequate for correct invocation.

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%, so the description does not need to compensate for missing parameter docs. It repeats some param names and adds the standalone-vs-invoice distinction, but the schema already documents invoice_ref as omit for standalone. Minimal added semantic value.

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: 'Issue a credit note against an invoice, or standalone.' It also distinguishes itself from credit_note_finalize by noting this returns a draft, so an agent can separate creation from finalization.

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 clear context for when to use it (to issue a draft credit note) and names the finalize sibling as the next step. It does not explicitly rule out update/delete or compare against all siblings, but the draft-vs-finalize workflow is clear enough.

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