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

Annotations are minimal (readOnlyHint false, destructiveHint false), so the description carries the burden. It discloses that SocialRobot fetches the bytes and stores them, which is a write operation, and that it returns a permanent URL. It also mentions the 50MB size limit. While it doesn't detail error handling or side effects, it covers the core behavior without contradicting the annotations.

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 concise yet packed with essential info: purpose, fallback context, input options, processing, output, preference, and size limit. Each sentence earns its place, with the core purpose front-loaded. No fluff or redundancy.

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?

The tool has no output schema, so the description must explain the return value, which it does ('returns the permanent url for create_post'). It also integrates with siblings get_media_upload_url and create_post, placing it in the workflow. It mentions the max file size. Missing details like error handling or parameter precedence are minor for a fallback tool with optional parameters. Overall, it is sufficiently complete for an agent to use correctly.

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 0%, so the description must explain parameters. It clarifies that 'file' is a ChatGPT file (object or array) and that 'sourceUrl' is a public https URL. It does not explicitly explain 'filename' and 'contentType', but these are optional and reasonably inferable. The description adds meaningful semantics for the key parameters, compensating for the lack of schema 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?

The description clearly states the tool's purpose: a fallback uploader that fetches bytes from a ChatGPT file or public URL and stores them, returning a permanent URL for use with create_post. It explicitly distinguishes itself from get_media_upload_url, which is the preferred direct PUT method. The verb 'upload' plus resource 'media' and the fallback context make the purpose unambiguous.

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 explicitly says when to use this tool ('Fallback when you cannot PUT to the presigned URL') and when not to ('Prefer get_media_upload_url when you can PUT'). It also states the output is intended for create_post, guiding the agent on the proper workflow. This is clear, actionable guidance with a named alternative.

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