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

Although annotations declare the safety profile (non-destructive, non-idempotent, closed-world), the description adds substantial behavior beyond them: bytes never traverse MCP, the caller must execute a returned PUT with exact bytes and returned headers, and explicit size caps per media type. It also warns against re-uploading on timeout, which is critical for a non-idempotent operation.

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?

Dense but front-loaded: format constraints, metadata requirements, size limits, and the PUT/poll workflow appear in that order with no filler. Every sentence carries procedural or constraint information an 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 multi-step tool with a nested metadata object and an output schema, the description supplies everything the schema cannot: how to consume the returned uploadRequest, how bytes are transferred out-of-band, and how to confirm completion via list_assets.

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?

With 60% schema coverage, the description compensates by explaining that metadata width/height are pixels and required for every asset and that durationMs is only needed for MP4, plus the 5 MiB / 100 MiB limits. filename and mimeType semantics are left to the schema, so it stops just short of full coverage.

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 (create one asset from a local file) and enumerates the accepted MIME types. It is clearly distinguished from siblings like list_assets, which is referenced only as the polling destination.

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?

Gives explicit preconditions (file must be available locally, convert SVG/GIF to PNG first), the required metadata per asset, and a precise post-call protocol including the 2-minute polling window and the fallback behavior when the asset is still uploading.

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