Open an isolated session

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

Since annotations carry no hints (all false), the description carries the full burden. It discloses the private BrowserContext, cookie/storage jar, popup tree, observation counter, and IDs, and explains that sessions are isolated and concurrent. It also states the requirement to pass sessionId. This is substantial transparency for a tool with no annotation assistance.

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: the first states the core action and return values, the second covers optional parameters and defaults, the third explains isolation and usage. It is front-loaded and each sentence adds essential information. Slightly longer than ideal but not wasteful.

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 an opening tool with no output schema, it explains what is returned (sessionId and environment), how to use the session (pass sessionId on every call), when to close it, and the concurrency benefit. The only minor gap is not detailing what 'environment' contains, but that is likely a return field described elsewhere. Overall, it is sufficiently complete for an agent 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 the baseline is 3. The description adds meaningful context: it states the defaults (1280×800, light, no-preference) and explains the purpose of the parameters ('configure responsive/media QA before navigation'). This goes beyond the schema's per-parameter descriptions, which only define types and enums.

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 verb (Open), a specific resource (independent browsing session), and the outcome (sessionId and environment). It clearly distinguishes itself from siblings like browser_open (which likely opens a page in a session) and browser_session_close (which closes a session). The purpose is unambiguous.

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 mentions the concurrency benefit ('several sweeps run AT THE SAME TIME without invalidating or authenticating each other') and gives direct instructions to 'Pass the returned sessionId on every call belonging to that sweep' and 'Close it with browser_session_close when done.' While it does not name alternative tools, the context clearly implies when to use this vs. a standard open.

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