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

Annotations already declare readOnlyHint, idempotentHint, non-destructive and closed-world, so the safety profile is covered. The description adds genuinely non-redundant behavior: the required scope 'document:read' and the fact that preview URLs are signed, which matters for how long the returned URLs stay usable.

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?

One dense sentence with the core action front-loaded and no filler. The appositive 'the ids prepare_fax returns' is slightly jammed in and reads as a comma splice, but nothing could be cut without losing meaning.

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?

An output schema exists, so the enumeration of returned fields is bonus rather than necessity, and the scope requirement is a useful addition. What's missing is error behavior — whether a not-yet-prepared or unknown document id errors or returns empty.

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 0%, so the single parameter is undocumented in the schema. The description compensates by defining the id's provenance ('the ids prepare_fax returns') rather than its format, which is the more useful constraint for an agent that must obtain the id first.

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 ('Fetch a prepared document by id') and immediately pins down which ids are valid ('the ids prepare_fax returns'), which distinguishes it from get_fax_status and read_inbound_fax. It also names the payload, so an agent knows what it gets back.

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 reference to prepare_fax as the source of valid ids effectively tells the agent the prerequisite step in the workflow. There is no explicit when-not-to-use or failure guidance (e.g. what happens if the document isn't prepared yet), so it falls short of full routing guidance.

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