Upload a local file

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

Annotations declare readOnlyHint=false, destructiveHint=false and openWorldHint=true, so the agent already knows this writes an external resource. The description adds genuinely useful context beyond that: exact size ceilings, allowed MIME types, and the billing note 'Uses no plan allowance', which affects whether the agent should call it freely.

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?

A single dense sentence front-loads the action, constraints, and return value, with the billing note last. Every clause carries information; nothing is redundant padding.

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 two-parameter upload tool with no output schema, the description covers formats, size limits, return value, and downstream usage. The only omission, the 'purpose' enum semantics, is already handled by the schema.

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 description coverage is 100%, so both parameters are fully documented in the schema. The description re-states the format/size rules for 'path' but says nothing about the 'purpose' enum (reference vs extend) or the 15s/8.7s video distinction, so it adds no meaning beyond structured data. Baseline 3 applies.

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?

Specific verb (Upload) plus resource (local file), enumerated accepted formats and size caps, and an explicit statement of what is returned (hosted URL). It is the only upload sibling, so differentiation is inherent, and the agent can understand the operation without opening the 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?

The description ties the output to concrete downstream uses (reference_image_urls, source_image_url), which tells the agent when this tool is relevant. It stops short of naming exclusions or competing tools, but no real alternative exists in the sibling list.

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