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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint, and destructiveHint. The description adds substantial behavioral context: it queries multiple live Peppol registers (including a retired one), explains interpretation of results, notes it is free and stores nothing, and states that every answer includes a disclaimer. No contradiction with 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 fairly long but well-structured: it opens with the core question, explains the operational scope, differentiates from a sibling, and ends with a disclaimer. While verbose, each sentence carries value and the key information is front-loaded. It could be trimmed slightly without losing content, but it is not padded.

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 read-only, idempotent tool with no output schema, the description covers all essential aspects: what it checks, the source of data, how to interpret different results, and what not to expect. The annotations supply the safety profile, and the description explains the nuanced distinction between current and retired lookups, making it fully actionable for an agent.

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?

The input schema provides 100% coverage of both parameters with detailed descriptions (scheme options, default, identifier format examples). The description does not add extra meaning about the parameters themselves; it focuses on the tool's purpose and interpretation. Given the schema coverage, a baseline of 3 is appropriate; the description adds context to the overall use case but not to parameter semantics specifically.

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 clearly states a specific verb (lookup/asks) and resource (Peppol participant registers), and explicitly differentiates from sibling check_peppol_ready. It also details what is returned (reachability, document types, escalation contact), leaving no ambiguity about the tool's function.

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 provides explicit guidance on when to use the tool (to check if a customer can receive an e-invoice via Peppol) and contrasts it with check_peppol_ready, which checks the user's own invoice offline. It also clarifies that the tool is not a promise of delivery, acceptance, or payment, setting correct expectations.

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