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

Annotations already cover readOnlyHint false, destructiveHint true, and idempotentHint true, so the description need not repeat those. It adds valuable behavioral context: rate/size limits ('Up to 50 URLs per call, 20 MB per file, 100 MB per call'), a warning that 'Signed CDN links expire', and a restriction on file types. This goes beyond the structured metadata without contradicting it.

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?

The description is efficient and front-loaded: it states the core purpose first, then the comparison, limits, exclusions, and caveats. Each sentence contributes new information, but it is a dense paragraph that could be slightly better broken out. Still, there is no fluff or repetition.

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 tool with only 2 parameters a rich schema and an output schema (not shown), the description covers the key non-obvious aspects: limits, file-type restrictions, signed-URL expiration, and legal guidance. It does not explain failure behavior or overwriting, but those are likely handled by the output schema and annotations, so the description is sufficiently complete.

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%, so both parameters (site and files, including url and path) are already fully documented in the schema. The description adds no new parameter-specific meaning beyond what the schema already states, such as path folder behavior. Baseline 3 is appropriate because the schema carries the weight.

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 begins with a specific verb-resource pair ('Downloads files from public http(s) URLs straight onto the website') and gives concrete examples (Instagram, Wix, Squarespace). It explicitly distinguishes itself from the sibling write_files by claiming to be 'Much faster than downloading and re-uploading them with write_files', making the tool's role clear.

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 description gives direct guidance on when to use this tool vs. write_files, and also states exclusions: 'Only for assets... PHP and server config files can't be imported.' It further advises timing for signed CDN links and legal usage, so an agent knows exactly the conditions under which this tool applies.

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