nex_browser_fill_account

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

With no annotations provided, the description carries the full transparency burden and succeeds richly. It discloses security boundaries ('keeps passwords and 2FA secrets outside MCP'), autonomy ('the plugin chooses the visible fields'), a critical non-action ('This tool never submits the form'), and the multi-step re-call behavior. This is genuinely valuable behavioral context beyond what structured data could convey.

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?

Four dense sentences, front-loaded with purpose, then prerequisite, repeat guidance, and a safety caveat. Every sentence earns its place; no filler. It is slightly long due to the workflow detail, but the structure flows logically from what→how→when→caveat.

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 tool with 3 optional params, no output schema, and no annotations, this description is remarkably complete: it covers the operation, the prerequisite sequencing, the security model, field-selection autonomy, repeated invocation across navigations, and the no-submit contract. The agent has everything needed to invoke it correctly without guessing.

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: it constrains accountId to 'only an accountId returned for this open window,' telling the agent where the value must come from — something the schema alone does not state. It also clarifies the optional-single-credential case. This exceeds what the schema provides.

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 states a specific verb+resource: 'autofill the current login page with a stored credential.' It clearly differentiates from siblings by emphasizing the vault-plugin aspect ('plugin chooses the visible fields') and by referencing the prerequisite nex_browser_accounts call, distinguishing it from manual fills like nex_browser_fill_form and nex_browser_fill_credentials.

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 provides explicit workflow guidance: 'Call nex_browser_accounts first and pass only an accountId returned for this open window' and 'Call again after each navigation in a multi-step sign-in.' It does not explicitly name alternatives to avoid (e.g., fill_form vs fill_credentials), but the context is clear enough for an agent to sequence correctly.

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