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

With no annotations the description carries the full burden, and it discloses meaningful traits: the session state persists ('leaves it open', 'controls references keep working'), cost ($0.005 plus outputs, $0.0002 cache hit), and the required close call. It does not touch auth/rate-limit or session-lifetime/expiry behavior, which would be the remaining gap for a stateful tool.

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?

Three sentences, zero waste, front-loaded with the core action and its statefulness, then the usage rule, then cost and cleanup. Every sentence earns its place.

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?

No output schema exists, and the description covers the return concept (map of controls), the persistent-session model, pricing and the close path. For a 6-param nested-schema tool it is nearly complete; session lifetime/timeout expectations and whether the returned controls survive navigation are unstated.

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 each parameter is already documented in the schema. The description adds only the conceptual 'controls references' note, not format/syntax guidance for wait, maxAge, formats or selectors. Baseline 3 is appropriate when the schema does the heavy lifting.

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+resource ('opens a browser on a page and leaves it open, returning the map of controls') and explicitly distinguishes the tool from read-only alternatives via 'when something has to be FILLED IN or CLICKED, not just read'. An agent can separate this from web_scrape/web_crawl without opening schemas.

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 an explicit when-to-use condition (interactive fill/click versus read) plus the lifecycle exit ('Close it with web_session_close when you are done'), naming the sibling responsible for cleanup. Nothing essential 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.