upload_image

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

Description explains beyond annotations: notes that the returned URL is publicly fetchable, unlisted, not attributed to user. Annotations indicate readOnlyHint=false (write) and openWorldHint=true, which description complements well, no contradiction.

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 purpose, every sentence adds value. No unnecessary words.

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?

With no output schema, description fully explains return value (hosted URL) and behavioral traits. For a two-parameter upload tool, it is complete and self-contained.

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%, but description adds clarity on mutual exclusivity and gives examples of data URI prefix and file path format, which goes beyond the schema's descriptions.

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?

Clearly states 'Upload an image to Substack's CDN' with specific verb and resource. Distinguishes from sibling tools, none of which involve image uploads.

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 to provide exactly one of two mutually exclusive parameters. While it doesn't explicitly state when not to use it, the context of siblings makes it clear this is the only upload tool.

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