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

Annotations only cover safety (readOnly, openWorld, non-idempotent), and the description goes well beyond them: it discloses the required public-https URL constraint, the mandatory email, a concrete quota (5 per email per day), the full enumeration of returned check categories, and an anti-prompt-injection note about extracted values.

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?

Dense but front-loaded: the core operation and the three-way-match boundary come first, then returns, then constraints. Every sentence carries distinct information — scope, sibling boundary, return format, quota, injection guard — with 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?

With no output schema, the description carries the full burden of explaining results, and it does so by enumerating header checks and all five line-level check outcomes. For a five-parameter tool with a quota and external URL inputs, an agent has everything needed to invoke it 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 coverage is 100%, so the baseline is 3, but the description adds real meaning: it explains why email is required (it is the quota and delivery key) and reinforces that both file parameters must be public https URLs rather than local uploads. It does not document the optional name/company fields, so it stops short of 5.

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 (compare) on two named resources (a purchase order and the invoice billed against it), scoped explicitly to the PO and invoice legs of a three-way match. An agent can place it precisely against parse_purchase_order, parse_invoice, and the calculation siblings without opening any 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 the when (comparing a PO to its invoice), the when-not boundary (this is only two legs of a three-way match; the goods receipt comparison must be done by the caller), and the input precondition (both files at public https URLs). Rate limit context is also supplied, leaving nothing to inference.

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