usable-browser-agent-free

browser_login

Fill username and password fields using a server-side secret alias, then submit the login form without exposing secret values.

Instructions

Atomically fill username/password fields from a server-side secret alias and submit the login form. Pass only refs and the secret alias; secret values are never accepted as tool input or returned.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "secret": "<secret>",
      "password_ref": "<password_ref>"
    },
    "name": "browser_login"
  }
}

Input Schema

Name	Required	Description
`secret`	Yes	Secret alias from the server-side secrets vault.
`submit_ref`	No	Submit button ref. If omitted, the password field's enclosing form is submitted.
`password_ref`	Yes	Password field ref, e.g. e12, from browser_snapshot.
`username_ref`	No	Username field ref. Filled only when provided and the secret has a username.

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.7.0Sep 9, 2026

TDQS

A4.2/5.0

Behavior3/5

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

With no annotations, the description carries the full burden. It discloses important behavioral traits: atomicity, the security policy of not accepting/returning secret values, and conditional filling of username. It does not mention error behavior, side effects like navigation, or what happens on failure, which leaves gaps.

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?

The description is a single efficient sentence that front-loads the main action and includes a critical security constraint. No filler or redundant information.

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?

Given no annotations and no output schema, the description covers the key aspects: what it does, security constraints, and parameter behavior. It omits failure handling and return value expectations, but for a login automation tool it is reasonably complete.

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 baseline is 3. The description adds meaningful context: explains that secret is a vault alias (not the value), that refs come from browser_snapshot, and that username_ref is only used when the secret contains a username. This goes beyond schema descriptions.

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

Purpose5/5

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

The description states a specific verb+resource: atomically fill username/password fields and submit the login form. It clearly distinguishes from siblings like browser_fill_secret and browser_fill_form by focusing on the login flow with a server-side secret alias.

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?

It gives clear context: pass only refs and the secret alias, and notes that secret values are never accepted as input. However, it does not explicitly exclude alternatives or state when not to use this tool, so it lacks explicit when-not guidance.

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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