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

With no annotations at all, the description carries the full burden and provides none of it: it does not say whether omitted fields are left untouched or cleared, does not warn that document_positions replaces ALL existing line items by default (a destructive side effect only documented inside the schema), and does not mention permissions, reversibility, or recalculation of totals. A mutation tool with zero annotation coverage needs far more.

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?

A single front-loaded sentence with zero filler. It is efficient, though the brevity reflects under-specification rather than disciplined editing.

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?

This is a 10-parameter mutation tool with no annotations and no output schema, meaning the description is the only place behavioral guarantees could appear, and it says nothing. Critical facts such as default replacement of all line items, partial-update semantics, and validation behavior are absent from the description text.

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 schema itself documents all ten parameters in detail, including the replace-vs-append policy, so the baseline is 3. The description only restates the id parameter ('by ID') and adds no semantics of its own.

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?

Names a specific verb and resource (update an invoice) and adds the lookup key (by ID), which distinguishes it from the many create_*/delete_* siblings in the namespace. There is no other update_invoice tool, so no sibling disambiguation is needed, but the description says nothing about what aspects of the invoice are updatable.

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 guidance on when to use this versus create_invoice, get_invoice, or the specialized update_* siblings. It also omits the prerequisite that the ID must come from search_invoices, a hint that only appears buried in the schema.

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