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

With no annotations provided, the description carries the full burden. It discloses the paid nature ($0.065 USDC on Base), the input constraints (up to 3 pages), the comparison behavior (expected purchase fields and line items), and the non-mutating outcome (no payment or bookkeeping action). It does not mention rate limits, failure modes, or what happens with invalid documents, but the core behavioral traits are well covered.

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?

The description is two sentences with no wasted words. It front-loads the most important operational facts (paid, format, page limit) and then states the comparison behavior and the non-action guarantee. Every sentence earns its place.

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?

The tool has 5 parameters, a nested expected object, an output schema, and no annotations. The description covers the input formats, the comparison logic, the output categories, and the non-mutating nature. It does not explain the output schema in detail, but the output schema exists and the description's summary of return categories is sufficient for an agent to select and invoke the 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 0%, so the description must compensate. It explains the purpose of the 'expected' object (expected purchase fields and line items) and the document input options (UBL XML or PDF/image). It does not detail each parameter's format or constraints, but the schema itself provides patterns and enums, and the description gives enough context to understand what the parameters represent.

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 states a specific verb ('check'), a clear resource ('paid invoice'), and the exact scope: UBL XML or PDF/image invoices up to 3 pages. It also names the output categories (evidence, amount checks, match/discrepancy/needs_review) and explicitly says no payment or bookkeeping action is taken. This distinguishes it from the sibling tools that handle more pages or provide quotes.

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 description clearly states what input formats are accepted (UBL XML or complete PDF/image invoices up to 3 pages) and what the tool does not do (no payment or bookkeeping action). It does not explicitly name the sibling alternatives or state when to choose invoice_preflight_10_pages or invoice_preflight_50_pages, but the page limit and the sibling names make the usage context reasonably clear.

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