invoices_attachments

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

Annotations already declare readOnly/idempotent/non-destructive, so the description's value-add is the return contract: base64-encoded binary plus MIME type, and the supported file-type range (PDF, images, Word, Excel, ZIP). That is genuinely useful beyond the structured fields. It omits any note on payload size or rate limits, which matters for large ZIP attachments, so not 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?

Four short sentences, front-loaded with the action and the return format, then the required-ID provenance, then supported types. Every sentence carries information the agent needs; nothing is redundant with the 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?

There is no output schema, so the description must describe the return value — and it does precisely (base64 binary with MIME type). Combined with the ID-provenance hint and the supported-type note, an agent has everything needed to call this correctly.

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% with all three parameters documented, so the baseline is 3. The description reinforces the attachmentId provenance and the invoice-level scoping of uuid, but adds nothing about the companyId override parameter that the schema already explains.

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 ('Download a file attachment from an invoice') and immediately disambiguates from the sibling that lists attachments by naming invoices_get as the source of attachment UUIDs. An agent can distinguish this from invoices_pdf or exports_download without opening any schema.

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?

Explicitly tells the agent where to obtain the required attachmentId ('Get attachment UUIDs from invoices_get (the "attachments" array)'), which is the main usage prerequisite. It does not state when NOT to use it or contrast with adjacent download tools (invoices_pdf, exports_download), so it stops short of full when/when-not guidance.

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