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

Annotations declare readOnlyHint=true, so safety is already covered, but the description adds genuinely new behavioral context: it discloses that the PDF attachment is never fetched, which prevents an agent from expecting binary content, and it surfaces the underlying endpoint (POST /api/v2/getinvoice), useful for error diagnosis.

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 tight sentences that front-load the returned content, with the endpoint tacked on as a single trailing clause. Every element earns its place; nothing is repeated from the title or annotations.

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 correctly carries the burden of describing the response shape at a useful level of granularity. It stops short of stating failure behavior (e.g. what happens for an unknown id), which is the main remaining gap for a single-record fetch tool.

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?

Single required parameter with 100% schema description coverage, including a UUID pattern and the source field (SIHId from merit_list_sales_invoices). The description adds nothing about the identifier beyond what the schema already states, so the baseline 3 applies.

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 ('One sales invoice in full') and enumerates the returned payload — header, lines with items/quantities/VAT/accounts, payments and dimension allocations. The 'in full' / single-record framing implicitly separates it from merit_list_sales_invoices and merit_search_sales_invoices, though none is named explicitly.

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, no prerequisites, and no mention of alternatives such as merit_list_sales_invoices or merit_search_sales_invoices. The only routing hint (that the id comes from merit_list_sales_invoices) lives in the schema, not the description.

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