Start session

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

With no annotations provided, the description carries the full behavioral burden, and it delivers: it discloses that each session is isolated, has its own cookies/audit history/action log, auto-closes after 5 minutes, and honors an env override. This goes well beyond what the schema alone conveys.

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 tight sentences, front-loading the core purpose and return value, then adding isolation and lifecycle behavior. Every sentence contributes useful information without 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?

For a session-starting tool with only two optional parameters and no output schema, the description is complete: it explains what is returned, how to use it, session isolation semantics, and auto-close behavior. An agent has enough to invoke 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 description coverage is 100%, so the baseline is 3. The main description adds no new parameter-level detail, but the schema already thoroughly explains alias sanitization, existing-id behavior, and the headless default. The description's mention of passing sessionId concerns the return value rather than the parameters.

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 uses a specific verb and resource ('Starts a browser session') and immediately states the key output (sessionId) and its role for subsequent calls. It clearly differentiates this tool from the many sibling action tools by establishing it as the session initiator.

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 explicitly instructs the agent to pass the returned sessionId to every subsequent tool call and lists representative siblings (navigate, click, type, run_a11y_audit). It also explains session isolation and idle auto-close, giving clear context for when starting a session is appropriate.

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