nex_browser_fill_credentials

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

With no annotations provided, the description carries the full burden of behavioral disclosure. It reveals that values are literal (implying they cross the MCP request boundary) and explicitly promises that no form submission occurs. However, it does not mention whether existing field values are overwritten or what happens on failure, which could be useful but is not critical.

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 a tight three sentences, front-loaded with the action, then a preference directive, then a behavioral caveat. Every sentence adds value, and there is no redundant wording.

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 an 8-parameter tool with no output schema, the description covers purpose, an explicit alternative, and a critical boundary (no submission). The schema documents target parameters, so that gap is mitigated. It could still describe failure behavior or return values, but the coverage is adequate for the tool's simplicity.

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 63%, with the three credential fields (username, password, totpCode) lacking descriptions. The description adds the concept of 'literal login credentials' but does not elaborate on parameter-specific usage or target resolution beyond what the schema already provides. This matches the baseline for high schema coverage.

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 ('Fill') with a clear resource ('literal login credentials') and scope ('visible fields'). It distinguishes itself from sibling nex_browser_fill_account by naming the alternative and highlights that it never submits the form, making the purpose unmistakable.

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 explicitly tells agents to prefer nex_browser_fill_account when a stored or bound account is available, providing a rationale ('literal values cross the MCP request boundary'). It also states a clear boundary ('never submits the form'), which helps decide when to use this tool versus alternatives.

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