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

Annotations already declare the mutation/safety profile (readOnly=false, destructive=false, idempotent=false, openWorld=true). The description adds behavior beyond them: batch execution with per-field failure reporting ('it reports which field failed'), which tells the agent how partial failures surface. It doesn't discuss authentication or the exact failure payload, so not a 5.

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 tight sentences, each earning its place: action+scope first, then the speed/behavioral rationale, then the disambiguation warning. Front-loaded and free of 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 2-param batch tool with full schema coverage and annotations covering safety, the description gives enough to select and invoke correctly. Minor caveat: it asserts 'there is no webpage_fill_form' while webpage_fill_form appears in the sibling list, which could momentarily confuse an agent about which batch tool exists for devices.

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 pageId ('Page ID from web_navigate') and fields ('in order') are already documented. The description only paraphrases pageId and the batch nature of fields, adding no selector syntax or field-format detail beyond the schema.

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 with scope: 'Fill several fields at once in the DESKTOP grid browser (by pageId).' It explicitly contrasts itself with web_type and webpage_type, so an agent can place it against siblings without opening a schema.

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 a direct when-to-use ('One call instead of a web_type per field ... faster on a long form') and names the alternative plus its condition ('on a real phone or tablet fill fields one at a time with webpage_type (by udid)'). No inference required.

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