Create a container (user context)

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

Annotations only supply readOnlyHint=false; the description carries the behavioral load and does so usefully by disclosing that the operation creates persistent state, that the new context isolates cookies and storage, and that cleanup requires a separate call. It stops short of saying whether creation is idempotent or what happens on failure, but the key mutation semantics are covered.

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?

Purpose and return value are front-loaded, but the phrase 'The id can be passed to browser_create_container style workflows' is self-referential and confusing inside browser_create_container's own description, and the trailing Firefox-account-tabs clarification is only loosely connected. One wasted/unclear clause in a short description costs it.

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?

For a zero-parameter creation tool with no output schema, the description covers what the agent needs: what gets created, what the return value is (an id), what the id is good for, and how to undo it. A brief note on context lifetime or limits would make it fully complete.

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 there is no parameter semantics to add and the baseline applies. The description correctly implies no configuration is needed to create the context.

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 and resource ('Create a new container / user context'), names the underlying BiDi primitive (browser.createUserContext), and notes the return value (its id). It also explicitly distinguishes the tool from browser_remove_container and from Firefox account tabs, so an agent can tell it apart from related siblings.

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?

Gives clear context: the returned id is what isolates cookies and storage and can be fed into follow-on workflows, and removal is routed to browser_remove_container. It doesn't mention browser_list_user_contexts or state when a container is preferable to, say, a fresh window/profile, so alternatives aren't fully enumerated.

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