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NexBrowser MCP Server

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nex_browser_fill_account

Autofills the current login page with a stored vault credential using an account ID returned for the open window; it never submits the form.

Instructions

Ask the NexBrowser vault plugin to autofill the current login page with a stored credential. Call nex_browser_accounts first and pass only an accountId returned for this open window; the plugin chooses the visible fields and keeps passwords and 2FA secrets outside MCP. Call again after each navigation in a multi-step sign-in. This tool never submits the form.

Input Schema

NameRequiredDescriptionDefault
pageIdNoDefaults to the active page
accountIdNoVault credential to use; optional when the open window has exactly one
sessionIdNoDefaults to the active session

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed2 schema fields changedv2026.10.24
    • changedInput schema / properties / pageId / description
      Previous value: -"Stable page ID; defaults to the session active page"New value: +"Defaults to the active page"
    • changedInput schema / properties / sessionId / description
      Previous value: -"Optional session ID; defaults to this MCP client active session"New value: +"Defaults to the active session"
  2. Changed4 schema fields changedv2026.8.19
    • changedInput schema / properties / accountId / description
      Previous value: -"Bound account to use; optional when the window has exactly one"New value: +"Vault credential to use; optional when the open window has exactly one"
    • removedInput schema / properties / passwordTarget
      Removed value: -{
-  "description": "Target of the currently visible password field",
-  "type": "string"
-}
    • removedInput schema / properties / totpTarget
      Removed value: -{
-  "description": "Target of the currently visible 2FA code field",
-  "type": "string"
-}
    • removedInput schema / properties / usernameTarget
      Removed value: -{
-  "description": "Target of the currently visible username field",
-  "type": "string"
-}
  3. Addedv2026.8.14

TDQS

A4.1/5.0
Behavior4/5

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

With no annotations, the description carries the load and does so well: it discloses that the plugin chooses fields, that passwords/2FA stay outside MCP, that the call must be repeated after navigation, and critically that the form is never submitted. Missing are failure behavior, what happens if no matching credential exists for the window, and any hint about the result.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Four tight sentences, each carrying a distinct fact (what it does, prerequisite, repeat-after-navigation, no submit), with the core action front-loaded. No filler or restatement of the tool name.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a small three-parameter tool with full schema coverage and no output schema, this covers the essentials an agent needs to call it correctly. The one gap is return/failure information — the agent cannot tell from the definition whether a success indicator or filled-field summary comes back.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so the schema already documents pageId/sessionId defaults and accountId optionality; baseline would be 3. The description adds real meaning the schema does not: the accountId must be one returned by nex_browser_accounts for this open window, which is a provenance constraint, not a restatement.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb+resource: autofill the current login page with a stored vault credential via the NexBrowser vault plugin. It distinguishes itself from generic input tools by noting the plugin picks the visible fields and that passwords/2FA never pass through MCP. It does not explicitly contrast with the closely named sibling nex_browser_fill_credentials, so an agent still has to infer which to use.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Gives an explicit prerequisite and sequence: call nex_browser_accounts first and pass only an accountId returned for this open window, and call again after each navigation in multi-step sign-in. That is clear operational guidance. It stops short of naming the alternative tool (e.g. nex_browser_fill_credentials) or stating when not to use this one.

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

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