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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint, and openWorldHint, but the description adds significant behavioral context beyond that: it is offline and free, it checks a subset of rules, and a clean result is not a guarantee of network acceptance. It also discloses what every finding contains (rule number, quote, suggested change), which is not in the schema or annotations.

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 about 150 words but every sentence carries value: the front-loaded purpose, the concrete rule examples, the output format, the cost/connectivity note, and the crucial limitation. It is dense without being bloated and earns its length given the tool's 11 parameters and complex domain.

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 11 parameters, nested objects, and no output schema, the description still provides a complete picture: what it checks, what findings look like (rule name, quote, change suggestion), and what a clean result does and does not mean. An agent can correctly decide to call this tool and understand the result without additional documentation.

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%, so the schema already documents every parameter in detail, including codes like BT-5 and BT-2. The description adds no additional parameter-level semantics; it merely alludes to fields like buyer reference and electronic address that are already fully described in the schema. A baseline 3 is appropriate when the schema does the heavy lifting.

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 opens with a clear use-case ('Before you send an e-invoice') and a specific verb ('Checks') against a well-defined resource ('21 published Peppol BIS Billing 3.0 rules'). It lists concrete failure examples and explicitly distances itself from the official validator, making it easy to distinguish from sibling tools like format_peppol_invoice or lookup_peppol_participant without opening their schemas.

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 gives explicit timing ('Before you send an e-invoice') and a clear purpose ('will the Peppol network accept it?'). It also provides an important exclusion ('not the official validator') and explains the limitation of a clean result. It does not name specific alternative tools, but the context is strong enough that an agent knows when to invoke this tool.

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