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

readOnlyHint: true already declares the safety profile, lowering the bar, but the description adds no behavioral context: no error behavior for a missing id, no note on what the line object contains. The REST endpoint string restates implementation detail rather than disclosing anything an agent needs.

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 short sentences, front-loaded with the core action. The second sentence (the raw endpoint) is borderline redundant with the tool name and could be dropped, but overall 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?

A simple single-param read tool where annotations cover safety and the schema covers the parameter, so the burden is light. However, with no output schema, the definition offers no hint of what a fetched invoice line returns, leaving a minor gap.

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% with a single required id param that already documents its source and pattern. The description's 'by id' adds nothing beyond the schema, so the baseline of 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 (fetch) and resource (invoice line) scoped by id, which clearly separates it from the plural halaxy_list_invoice_lines sibling. It does not explicitly name that alternative, but the singular 'by id' framing makes the distinction inferable.

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?

No explicit guidance on when to use this versus halaxy_list_invoice_lines or halaxy_get_invoice. The only contextual hint ('from the matching list tool') lives in the schema, not the description, so the description itself leaves usage to inference.

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