Read an e-invoice

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

Annotations already indicate readOnlyHint, openWorldHint, idempotentHint, and destructiveHint=false. The description builds on this by disclosing the upload over HTTPS, in-memory processing and discard, the API key requirement, the 10 MB refusal, and rate-limit/429 behavior. These context-rich details meaningfully exceed what annotations alone convey.

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 long but every sentence carries functional weight: output contents, usage advice, side effects, constraints, and error handling. The primary result is front-loaded before operational caveats, though it could be trimmed slightly without losing value.

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 single-parameter read-only tool with no output schema, the description is complete: it lists the return fields, the supported input file types, failure modes, security/processing behavior, authentication requirement, and rate-limit behavior. An agent has everything needed to decide whether to call it and what to expect.

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%, and the schema already thoroughly documents the single 'path' parameter, including accepted extensions and the plain-PDF error case. The description adds no additional parameter meaning beyond that, so the baseline score of 3 is appropriate.

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 ('Extract') and resource ('one electronic invoice file') and enumerates exactly what will be returned, including the EN 16931 check and the visible-page-vs-XML comparison. It also differentiates itself from its only sibling, check_invoice, by explicitly contrasting content extraction with a verdict-only tool.

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?

Explicitly states when to use the tool: 'Use it when the user wants to know what an invoice contains.' It also tells the agent when not to use it and names the alternative: 'If they only ask whether the invoice is correct, use check_invoice instead.' Additional constraints such as file size and 429 handling round out the guidance.

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