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

Annotations only mark the operation as non-read-onlyasi, but the description adds meaningful behavioral detail: uploads go through the existing MCP session host, there is a ~20MB size ceiling, and corrupt bytes should not be uploaded. It also discloses the successful result shape by mentioning the returned file_id.

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 front-loaded with its core purpose and every sentence serves a purpose, including alternatives, constraints, and validation guidance. It is somewhat dense and repeats part of the schema's decoding warning, and the phrase 'for file_ids' is underexplained, which keeps it from being perfectly concise.

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 this complexity, the description covers the key decision context, constraints, corruption handling, alternatives, and expected output. The presence of an output schema means return-value details do not need to be restated, and nothing essential for correct invocation 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 already 100%, so the baseline is a 3. The description adds some value by emphasizing local decode checks and the size limit, but much of the base64-integrity warning is already present in the data_base64 parameter description, so the extra semantic lift is moderate.

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 clearly identifies upload_data as a base64, API-host upload that returns a file_id, and differentiates it from the presigned-PUT path and asset_files usage on create_design/update_design. The 'remote-safe' qualifier and base64 mechanism make its role specific and distinguishable from related upload tools.

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 exactly when to use the tool—sandboxed clients whose egress blocks PUTs—and when not to: files over ~20MB or cases where a presigned PUT is possible. It also gives a concrete pre-upload validation workflow, telling the agent to decode locally and report corruption instead of uploading.

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