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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive), and the description adds genuine behavioral context beyond them: a ~5 MB size cutoff and the fact that the base64 payload is deliberately omitted to protect the MCP transport. It doesn't mention auth/permission requirements, so it falls short of a 5.

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 sentences, both earning their place: the first defines scope, the second defines the output-degradation rule. Front-loaded with the primary action and no redundant restatement of the name or title.

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 three fully described parameters, no output schema, and annotations covering the safety profile, the description supplies exactly the missing pieces: what the return payload is (base64) and when it is replaced by name/size. Nothing an agent needs to call this correctly is absent.

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 baseline is 3, but the description adds meaning the schema lacks: the concrete ~5 MB threshold and the consequence (name and size only) of setting metadata_only=true or exceeding the size limit. The entity_type and id parameters are already fully documented by the schema.

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 (download) and resource (source document) and enumerates the four entity types it covers (purchase invoice, sale invoice, journal, bank transaction). This scope statement distinguishes it from the narrower sibling get_sale_invoice_document, so an agent can pick between them without opening schemas.

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 implies usage through the entity_type enumeration and explains the metadata_only branch, but never states when to prefer this tool over get_sale_invoice_document or get_sale_invoice_xml. Usage is inferable but not routed explicitly.

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