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

Annotations already declare readOnlyHint=false, destructiveHint=false, and openWorldHint=false, so the safety profile is covered. The description usefully clarifies the resulting state ('not sent, not marked paid') and hints that a review link is returned, which matters since there is no output schema, but it says nothing about idempotency semantics for idempotencyKey or any permission requirements.

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 short sentences, front-loaded with the core action and its scope. The state clauses ('not sent, not marked paid') earn their place by preventing incorrect assumptions about side effects, though the phrasing is a bit repetitive.

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 an 8-parameter mutation tool with 0% schema description coverage and no output schema, the description is far too thin. It omits required-parameter expectations (items structure with description/quantity/unitPrice), currency handling, date semantics, and idempotency behavior — all things an agent needs to invoke this 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 0% across 8 parameters, so the description carries the full burden and largely fails it. Only clientId is obliquely addressed via 'a customer who is already in this business'; items, currency, dates, notes, and especially idempotencyKey get no explanation at all.

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 verb and resource ('Save a draft invoice') and adds a scope condition ('for a customer who is already in this business'). It does not explicitly distinguish itself from the nearest sibling, create_draft_estimate, so it stops short of a 5.

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 phrase 'for a customer who is already in this business' implies a precondition (the client must already exist) and by extension the find_clients flow. However, there is no explicit when-to-use guidance or direction to the alternative create_draft_estimate for estimates.

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