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

Annotations declare readOnlyHint=false, and the description explains exactly why: "It marks the fax read for the person" — a disclosed side effect that the annotations alone would not make obvious. It further adds the return shape (pages as images, capped at 10), an authentication prerequisite (the person must sign in to Faxette), and a handling constraint on sensitive content.

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: selection rule first, then return format, then side effect, then handling and auth constraints. Every sentence carries distinct operational information, with no restatement of the title or name.

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 supplies the return format (pages as images, up to 10), the state change it causes, and the sign-in requirement — the three things an agent could not infer from the structured fields. Nothing needed to call it correctly is missing.

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%, and the schema already explains both parameters including their source tools (get_inbound_faxes, get_organizations) and the disambiguation prompt. The description adds no parameter-level meaning beyond that, 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?

"Use this only when the person asks what a received fax says, or to summarize it" plus "Returns its pages as images, up to 10" states a specific verb (read/return content) and resource (a received fax) with scope. It implicitly separates content retrieval from the metadata-oriented siblings like get_inbound_fax and get_inbound_faxes, so an agent can route without opening a 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?

Explicit trigger condition ("only when the person asks what a received fax says, or to summarize it") and an explicit constraint on how the content may be used (don't repeat medical or legal contents beyond need). It lacks a named alternative for the adjacent case, e.g. pointing to get_inbound_fax when only metadata is wanted, which keeps it from a 5.

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