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

Annotations already declare readOnly, idempotent, non-destructive and non-open-world, so the safety bar is low. The description still adds real value by disclosing the return shape (step-by-step screens, buttons, fields) and the crucial behavioral fact that it 'opens nothing by itself' and must be paired with cotlet_browser_* tools to take effect — something the annotations cannot convey.

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 core message is delivered in two sentences, but the opening sentence is overloaded (platform list, account scoping) and buries the key 'returns instructions, doesn't act' point mid-paragraph. The trailing sentence about 404s on gymdesk.com/api and the help center is verbose research meta-commentary that only weakly supports the browser-tool rationale.

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 zero parameters and no output schema, the description carries the burden of explaining what comes back, and it does ('step by step (screens, buttons, fields)'). It also explains why a browser tool is needed instead of an API, which is relevant given the absence of a documented Gymdesk API. The only shortfall is that it does not clarify the boundary with the website-domain/white-label sibling.

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?

The tool takes zero parameters, so the baseline of 4 applies. Nothing in the schema requires explanation, and the description correctly does not invent parameter detail.

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?

Names a specific verb and resource ('configure custom email domain') and disambiguates from the similarly named website-domain sibling by scoping it to email. However, the opening clause ('Configure custom email domain in the user's own Gymdesk account') implies the tool performs the change, and only the later clause ('Returns how to do it ... opens nothing by itself') corrects that to a guidance-only tool, so the purpose is clear but not front-loaded.

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?

It does tell the agent what to do next ('then do it with the cotlet_browser_* tools in the user's Gymdesk Cloud Browser'), which is useful sequencing guidance. But it never states when to call this versus the sibling that sets up a custom domain and white-labels the website, nor any precondition or exclusion, so the choice between siblings is left to inference.

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