form_fill

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

The description discloses the label-matching heuristic (nearest input field, checkbox/dropdown handling) which is useful behavioral context. However, it doesn't describe failure modes (what happens when a label isn't found, partial fill behavior), and given readOnlyHint=false and no destructiveHint, the mutation behavior is only implied rather than stated. Schema coverage is complete but behavioral risks like non-reversibility aren't addressed.

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, tightly written, front-loaded with the core purpose. The first sentence states the action, the second explains the mechanism, the third notes special field handling. No wasted words or redundancy. Slightly more could be said about failure behavior, but structurally this is efficient.

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?

Given openWorldHint=true, the description should disclose more about what's NOT guaranteed. It explains the mechanism reliably but omits behavior under edge cases (unfindable labels, unsupported field types, empty values, behavior on submission). No output schema details are needed since one exists, but the description could state that partial fills may occur silently.

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 all three per-field parameters and the serial field are documented in the schema. The description adds value by explaining the 'type' semantics (text/checkbox/dropdown handling via label matching) rather than just listing them, but the description doesn't elaborate on 'serial' beyond schema. Baseline 3 is appropriate when schema covers all 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+resource ('Fill a multi-field form') and clearly explains the mechanism (array of label/value pairs, finds nearest input, taps, types). It distinguishes from siblings like input_text (single field) and ui_smart_fill by describing the batch multi-field behavior, though it doesn't explicitly name an alternative.

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 description implies usage context (batch form filling with label-based field matching) but provides no explicit when-to-use vs alternatives, no exclusions, and no guidance on when this would fail (e.g., ambiguous labels, missing serial requirement). No mention of when to prefer ui_smart_fill or input_text.

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