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 only the raw HTTP path (GET /main/Invoice/{id}), which conveys nothing behavioral beyond the annotations — no mention of what happens on an unknown id, whether the response is a single object or wrapped, or any permission requirements.

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, front-loaded sentences with no filler. The second sentence restates the resource in path form rather than adding information, a small redundancy but not harmful.

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 annotations covering safety, this is roughly adequate, but there is no output schema, so the agent has no idea what an invoice record contains or how errors surface. A brief note on the returned shape or a pointer to related tools would close the 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% and the single id parameter is documented with format and origin ('from the matching list tool'), so the schema carries the load. The description adds no parameter-level meaning, which is acceptable at full coverage but earns only the baseline.

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 gives a specific verb and resource ('Fetch an invoice by id'), which is unambiguous. It does not distinguish the tool from its obvious sibling halaxy_list_invoices or explain why one would retrieve a single invoice instead of listing.

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?

There is no indication of when to use this tool versus halaxy_list_invoices or halaxy_get_invoice_line, and no prerequisites such as needing an id obtained elsewhere. The only hint at usage comes from the schema description ('from the matching list tool'), not the tool description.

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