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

Annotations already declare readOnlyHint=true, openWorldHint=true and destructiveHint=false, so the safety profile is covered. The description adds only the media types; it says nothing about authentication needs, rate limits, or where/how the retrieved media is delivered. On the lower bar set by the annotations, this still adds very little behavioral context.

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?

A single tight sentence with the action and scope front-loaded and no wasted words. It is efficient, though it could have used a few of those saved words on usage or delivery behavior.

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 an output schema present, return values need not be explained, and a one-parameter download tool is inherently simple. Still, nothing is said about authentication, URL validity, or supported URL forms, leaving modest gaps for an openWorld fetch tool.

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 a single required 'url' parameter with full schema description coverage, so the schema already documents the input. The description's phrase 'from Facebook URLs' merely echoes that, adding no format or validation detail beyond the schema; the baseline of 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?

The description gives a specific verb (Download) plus the resource and subtypes (images, videos, audio) from Facebook URLs. This clearly separates it from the surrounding get_/search_ siblings, which are all read-only lookups rather than downloaders, though it does not explicitly name an alternative.

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?

It states what the tool does but offers no when-to-use guidance, no prerequisites (e.g. auth or accessibility of the URL), and no mention of when another sibling would be preferable. An agent gets no routing help beyond the obvious 'this is the download tool'.

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