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

Annotations already flag destructive, openWorld and non-idempotent; the description adds value beyond them by disclosing the return payload (URL and title) and the cost/lifecycle model (credits per started minute, session closes or ends 3 minutes after the last call). It does not explain what the destructive hint means in practice, such as whether an existing file is replaced.

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?

Three dense sentences with the action and target front-loaded, followed by input format, limits and cost. Every sentence carries information; no repetition of the schema's property text.

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?

No output schema exists, yet the description still names the return values, and it covers input limits, accepted formats, and billing/session behavior. An agent has everything needed to decide to call and to call it 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 coverage is 100%, so baseline is 3; the description earns one extra by supplying the 20 MB per-file cap, which the schema does not state, and by concretely illustrating both accepted file object shapes. Element addressing is left to the schema.

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 (puts files into) and precise resource and target: a file field on the current page of the Substack Cloud Browser, or the picker an upload button opens. The browser context distinguishes it from the sibling cotlet_upload_file, though the relationship is only implied via the file_id mention rather than stated.

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?

Explains the two concrete situations that select this tool: targeting an existing file input element, or triggering an upload-button picker. It implies the cotlet_upload_file prerequisite for file_id without naming it as an explicit alternative path.

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