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

With no annotations, the description carries the full burden and does well: it discloses failure semantics ('stops at the first failure and tells you where'), that it returns resulting state, and pricing ('$0.0005 per action'). It omits session-expiry or permission behavior, but the core behavioral traits 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?

Extremely dense and front-loaded: purpose first, then the action grammar, then the ref provenance, then failure and pricing. Every clause earns its place with no filler.

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 multi-action mutation tool with no annotations and no output schema, the description covers the essential invocation surface (action grammar, failure behavior, cost). It could say more about the shape of the returned 'resulting state', but that gap is modest given the tool's scope.

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 baseline is 3, but the description adds real meaning beyond the schema: the `actions` items are untyped objects in the schema, and the description supplies their shape ({click:{ref}}, {type:{ref,text,clear}}, etc.) and clarifies that `ref` comes from the `controls` output. This compensates for the schema's generic array items.

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 ('runs actions') and resource ('an open session') and enumerates the exact action vocabulary (navigate, click, type, select, press, scroll, wait, back). This clearly separates it from siblings like web_scrape, web_crawl, and web_session_open, which don't operate on an already-open session.

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 phrase 'against an open session' implies the prerequisite that web_session_open must run first, and the action list implies interactive driving. However, it never explicitly states when to use this over web_scrape or web_batch, nor any when-not conditions.

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