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

The annotations already declare readOnlyHint=true, so the safety profile is covered. The description adds only the REST endpoint path, which is structural trivia rather than behavioral context such as error behavior when the id is unknown or the shape/limits of the response.

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 ('Orb API: GET /invoices/{invoice_id}') is largely redundant for an agent and does not earn much of its place.

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 simple one-parameter read tool this is close to adequate, but with no output schema the description says nothing about what the invoice object contains or what happens on an invalid id, leaving an avoidable 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% for the single invoice_id parameter, so the schema carries the burden. 'By id' adds no format, prefix, or example detail beyond what the schema already states.

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 ('Fetch a single invoice by id'), clearly distinguishing a single-record fetch from list operations. It does not, however, differentiate itself from close siblings like orb_get_upcoming_invoice or orb_list_invoices.

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 when-to-use guidance is given. An agent must infer from 'single' that this is not a list call, and nothing tells it when to prefer this over orb_list_invoices or orb_get_upcoming_invoice.

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