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

Annotations already declare readOnlyHint=true, so the read-only nature needs no restating. The description adds useful context by enumerating what the response contains (line items, totals, balance, dates, status, invitations), but says nothing about auth requirements, error behavior for unknown ids, or rate limits.

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 compact sentences with the resource and scope front-loaded and the endpoint appended as supporting detail. Nothing is redundant or 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?

With no output schema, the description usefully summarizes the returned fields, which is the main missing structured data. It is nearly complete for a single-entity read, lacking only edge-case behavior for invalid or missing ids.

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 single parameter is fully documented in the schema (hashed id with example), so the description only echoes 'by id'. Baseline 3 is appropriate when the schema carries the parameter semantics.

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 (one invoice) with the identifier qualifier 'by id', clearly distinguishing it from invoiceninja_list_invoices. The endpoint reference (GET /api/v1/invoices/{id}) reinforces the single-resource scope.

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?

The phrase 'one invoice by id' implies when to use it versus list_invoices, but the alternative is never named and no prerequisites (e.g. needing the hashed id from a list call) are stated. Usage is inferable rather than explicit.

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