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

Annotations declare readOnlyHint=true, openWorldHint=false, idempotentHint=true, and destructiveHint=false, so the safety profile is already covered. The description adds important behavioral context beyond annotations: nothing is typed into the chat; the user signs in or signs up on teas.co.uk in an assistant-opened window. This is useful operational detail for an agent. It stops short of describing the return format or what happens on failure.

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 three sentences and front-loads the trigger condition, but it is somewhat repetitive: the first and second sentences both cover what an account gives and how to link or create one. It could be tightened without losing meaning. Still, it is not bloated and remains readable.

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?

Given zero parameters, rich annotations, and an output schema, the description need not explain return values. It covers the trigger, the account-linking behavior, the out-of-band sign-in flow, and the fact that shopping works without an account. It is nearly complete, though it does not state what the output schema returns or what happens if the window is closed.

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 is 4. The schema is empty and fully covered, and the description correctly implies no input is collected from the chat. No parameter-related gaps exist.

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 states a specific resource and the question it answers: whether a teas.co.uk account is linked, what it adds, and how to create or link one. It is clear what the tool does, though it does not distinguish itself from siblings by name (e.g., login/account tools) beyond the account-linking scope. No sibling appears to overlap directly with this onboarding/account-explanation purpose.

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 provides clear usage context: use it when someone asks about account benefits, creation, or linking, and it explicitly notes that searching, basket, and checkout work without an account. This helps the agent avoid calling it for shopping operations. It does not name specific alternative tools, but the when-to-use condition is well stated.

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