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

The readOnlyHint annotation already establishes that this is a safe read operation, so the description only needs to add context beyond that. It adds the "at least one" filter requirement and exposes the underlying POST endpoint, but says nothing about matching behavior (exact vs partial), result ordering, or pagination semantics.

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 compact sentence carries the purpose, keys, and constraint; the trailing endpoint path is low-value but harmless. Nothing is buried 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?

For a four-parameter read-only search with full schema coverage and no output schema, the description covers the essentials: what it finds, by which keys, and the minimum input requirement. The main omission is routing guidance relative to the list/get siblings, which is a modest gap rather than a blocker.

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%, so the parameter details are already documented, but the description adds a genuine cross-parameter constraint the schema lacks: at least one of invoice_no, customer_id, or customer_name must be supplied (the schema declares zero required fields). That elevates it above the baseline 3.

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 names a specific verb+resource ("Find sales invoices") and the three search keys, so an agent can tell this is a lookup-by-identifier tool. It does not explicitly distinguish itself from siblings like merit_list_sales_invoices or merit_get_sales_invoice, leaving that inference to the reader.

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?

"give at least one" provides a useful invocation constraint, but there is no explicit when-to-use guidance, no mention of alternatives (e.g., use merit_list_sales_invoices to enumerate all invoices), and no statement of when this tool is inappropriate.

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