start_login

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

Beyond the annotations (readOnlyHint=false, openWorldHint=true), it discloses behavioral traits the annotations cannot: the window is visible, the user types credentials by hand, 'The agent never sees the password', and read_only constrains the agent from typing, submitting, sending or buying. That is exactly the kind of secret-handling and capability-boundary context an agent needs.

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 purpose sentence is front-loaded and the per-parameter lines are dense but each earns its place. It runs longer than strictly necessary, and the profile line stacks several sentences that could be tightened, but there is no filler.

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?

The tool is a multi-step human handoff with four optional/required parameters and an output schema that covers return values, and the description supplies the full workflow (start, user logs in, call complete_login), the secret model, and the capability limits. Nothing an agent needs to invoke it correctly is missing.

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 description coverage is 0%, so the description must carry all parameter meaning, and it does: url is the login/home page, profile is a saved name with an empty-means-derive-from-account rule, allowed_domains defaults to the url's base domain and bounds navigation, and read_only defines what the agent may not do. Every one of the four properties is explained with behavior, not just a restatement of the type.

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 and resource ('Open a visible browser window') and immediately scopes the intent to a human-in-the-loop login, which cleanly separates it from the agent-driven open_session and from the follow-up complete_login. An agent can pick it without opening any schema.

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?

It names the completion step explicitly ('Call complete_login once the user says they're done') and explains the repeat-login case ('Log in again with no name to add another account'). It never explicitly contrasts itself with open_session or the other sibling session tools, so the when-not is implied rather than stated.

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