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

Annotations declare readOnlyHint=false, openWorldHint=true and destructiveHint=false, so the description doesn't need to restate the write/safety profile. It adds genuine non-obvious behavior instead: that a budget is held while the call runs and released afterward, and that the fetched asset stays reference material by default. It doesn't describe failure/refund behavior if the fetch fails, which keeps it from a 5.

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?

Three sentences, front-loaded with the action and media types, then scope/cost facts. Every sentence carries information; no filler. Slightly terse on routing, but well structured.

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 return values need not be explained. Combined with annotations covering safety and the schema covering params, the description supplies the remaining context an agent needs: cost handling, access scope, and the reference-vs-publish stance. Only the sibling-routing guidance 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 coverage is 100%, so all three parameters are already documented, including the budget default/max and the enum semantics for 'purpose'. The description mostly restates those (the budget hold, the reference-material default). Baseline 3 is correct when the schema carries the parameter documentation.

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: pull an image, video, audio file or PDF at a public URL into the media library as a media key. The media types and the resulting artifact ('media key') make the operation unambiguous. It does not explicitly name or contrast a sibling (e.g. assets_upload), so it falls short of a 5.

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?

'A fetched file is reference material until you know you may republish it' gives useful framing about intent, and 'Needs the write scope' is a real precondition. However, it never says when to pick this over the nearby siblings assets_upload, reference_search, or list_page_assets, leaving the routing decision implied.

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