form_fill

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

With no annotations provided, the description carries full burden and does so admirably: it discloses case-insensitive matching, specificity ordering, ambiguous-key handling, submit behavior, password masking, and the fallback behavior. This goes well beyond a basic 'fill a form' statement.

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 dense but every sentence earns its place. It front-loads the primary purpose, then covers matching, submit, security, and fallback in a logical order. No filler or redundancy.

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 the tool's complexity, the description is complete: it covers prerequisites (tabId from tabs_context), input format, matching behavior, submit option, password masking, and fallback. It even mentions refs in the result for fallback, aligning with the output schema. No gaps identified.

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%, but the description adds substantial meaning beyond the schema: it explains the fields map semantics (labels, placeholders, name attributes), value types, matching logic (case-insensitive, specificity-ordered, ambiguous keys returned unmatched), and the result's refs for fallback. This enriches the schema's bare parameter list.

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 opens with a specific verb+resource+method: 'Fill a form by field labels in one call.' It clearly distinguishes from sibling tools like form_input by describing the one-call batch-fill approach and the fallback to form_input for unmatched fields.

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?

Explicitly names an alternative tool (form_input) for unmatched fields and instructs to use tabs_context first for a valid tabId. It also clarifies when submit:true is relevant and how the matching works, giving clear context for when to use this tool.

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