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

Adds meaningful behavior beyond the annotations: the URL is one-time, valid for 30 minutes, accepts multipart field 'files', and caps at 10 files per request. It doesn't cover auth requirements or what happens on expiry, but it substantially enriches the safety profile already supplied by readOnlyHint=false, destructiveHint=false, and openWorldHint=true.

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?

Two sentences, front-loaded with the core action and return value, followed by the routing guidance. Every clause carries useful information with no 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 simple two-parameter tool with no output schema, the description covers what is returned, how long it is valid, how to use it, and when to prefer it. Minor gaps around auth headers and failure modes remain, but the essential calling context is present.

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 app_id and replace are already documented in the input schema. The description adds operational detail about the URL's 'files' field and the 10-file limit, but does not clarify the tool's own input parameters beyond that. Baseline 3 is appropriate when the schema does the heavy lifting.

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: returns a one-time upload URL. It explicitly distinguishes itself from the sibling upload_screenshots by naming the alternative and the condition that selects it, so an agent can route correctly without opening either schema.

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 when-to-use guidance: prefer this over upload_screenshots when a shell is available, so large images don't pass through the conversation. The alternative and the routing condition are named directly.

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