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

Annotations already declare readOnly, idempotent, and non-destructive, so the safety profile is covered. The description adds genuine behavioral value beyond that: the return is base64 bytes and is capped at 10 MiB, which is a real constraint an agent must plan around. It would be a 5 if it said what happens at the size limit (truncation vs. error), but the added constraint is substantive.

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 short sentences with zero filler, and the action is front-loaded before the return detail. Every clause carries information the agent needs.

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-parameter tool with annotations and an output schema, the description covers what the tool does, how it is keyed, and its payload shape and cap. The remaining gap is the error/truncation behavior at 10 MiB and how the ID is sourced, but the output schema carries the return-value burden.

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?

There is one parameter at 0% schema description coverage, so the description must compensate. 'By saved ID' tells the agent this is an identifier of a previously saved attachment rather than a path or URL, but adds nothing about the format constraints (pattern, 1-128 chars) or where the ID is obtained, leaving the single parameter only partially explained.

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 field attachment') plus the keying mechanism ('by saved ID'), which separates it from the list_field_attachments sibling. It does not explicitly distinguish itself from other download_* siblings (download_resource, download_location_document), so the differentiation is inferred from the resource noun rather than stated.

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?

Usage is only implied: 'by saved ID' hints that an ID must come from somewhere (presumably list_field_attachments), but the description never says to call that first or when to prefer this over the other download tools. No exclusions or prerequisites are given.

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