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

Annotations already declare readOnlyHint=false, destructiveHint=false, openWorldHint=true, idempotentHint=false, so the safety profile is covered. The description adds real value beyond that: uploads consume the caller's storage quota, bytes land on a CDN, and the call bypasses the widget that normally supplies the argument. It stops short of describing failure modes or quota exhaustion behavior, so a 4 rather than 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?

The do-not-use warning and the mechanism are front-loaded in the first sentence, and the follow-up sentence routes the agent to the correct tools. No filler sentences.

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?

Output schema exists so return values need no explanation, annotations cover the safety profile, and params are fully documented in schema. The description supplies the one thing structured data cannot: this is an internal endpoint the agent should route around.

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% and the nested items document data, name, size, and type with fallback behavior for blank names. The description only restates that the payload is base64-encoded, which the schema already declares via contentEncoding, so it adds little beyond baseline.

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 concrete verb and resource ('stores them on Postey's CDN under the caller's storage quota') and immediately frames the tool as an internal widget endpoint, which separates it cleanly from file_manager and upload_media.

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?

Explicitly says 'Not for direct model use', then names both alternatives and the conditions that select them (file_manager for the drop widget, upload_media for public URL or base64). It also warns that calling it directly bypasses the widget that produces its argument.

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