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

readOnlyHint=true is consistent with a GET. The description adds real behavioral value beyond annotations by disclosing that the response embeds line items and attachments rather than returning a bare invoice record — important since there is no output schema. It doesn't cover not-found or error behavior, which keeps it below a 5.

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?

Two sentences, zero waste, with the payload contents front-loaded before the endpoint detail. 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 single-parameter read tool with a readOnly annotation and no output schema, the description covers what is returned (invoice plus line items and attachments) and how to address it. Only the absence of error/empty-result behavior keeps it from full marks.

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 schema already explains that invoice_id comes from gorelo_list_invoices. The description adds no format, constraint, or sourcing detail beyond that, so the 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 invoice") and adds scope detail by naming what comes back: line items and attachments. This implicitly separates it from gorelo_list_invoices, though it never names that sibling explicitly.

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 can infer this is the single-record fetch and that the id comes from gorelo_list_invoices, but only because the schema says so. The description itself gives no when-to-use or when-not-to-use guidance relative to the list tool.

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