Download invoice PDF

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

The annotations already declare readOnlyHint=true, and the description adds meaningful behavioral context beyond that: the PDF can be saved locally or returned inline, and language selection affects the document. This clarifies the local side effect while remaining consistent with the read-only hint.

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?

The description is a single concise sentence that front-loads the action and resource, then adds the two most important behavioral options. Every clause earns its place without redundant filler or schema repetition.

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 single-resource download operation with four well-documented parameters, the description covers the core behavior and output modes sufficiently. Since there is no output schema, a brief note on return values is present via 'save it locally (or return it inline)', which is adequate; error handling or prerequisites are not essential here.

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%, so the parameters are already fully documented in the input schema. The description's mention of Bulgarian/English and inline vs. local save restates what the 'language' and 'delivery' parameter descriptions already provide, adding no new semantic detail.

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 uses a specific verb ('Download') and resource ('PDF of an invoice'), and adds scope with Bulgarian/English language support and two output modes (save locally or return inline). This clearly differentiates it from sibling tools like nula_search_invoices and nula_lookup_company, which operate on search/lookup rather than file retrieval.

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 description makes the tool's purpose immediately clear: retrieve an invoice PDF. It does not explicitly state exclusions or alternatives, but none are needed because no sibling tool offers PDF retrieval; the closest siblings are for searching or listing invoices, so the usage context is unambiguous.

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