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

readOnlyHint=true already tells the agent this is a safe read. The description adds genuine value by disclosing that the response embeds related data (line items, billing address, payment term), which the agent could not know otherwise. It says nothing about behavior on a missing or invalid id, so it remains thin beyond that.

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?

A single sentence with no filler; the resource and scope lead, and the returned fields follow. Nothing could be removed without losing information.

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 one-parameter read tool with no output schema, the description covers the essentials: what is fetched and which related records are included. It lacks only edge-case behavior (not found, permissions), a minor gap at this complexity level.

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% and the id parameter already carries a description pointing to papierkram_list_invoices as the source. The prose adds no format, type or constraint detail beyond the schema, so baseline 3 applies.

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 and resource ('Get one outgoing invoice') and enumerates what comes back (line items, billing address, payment term). The singular 'one outgoing invoice' implicitly contrasts with papierkram_list_invoices, but it never names that sibling to make the distinction explicit.

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?

Usage is only implied: an agent infers this is the single-record fetch to use once it has an id. There is no explicit when-to-use vs papierkram_list_invoices, nor any stated prerequisite such as needing an id first, though the schema hints at it.

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