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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so repeating 'Read-only' adds little. The description's real value is the explicit negative guarantee about what is withheld (email, tokens, cookies, page content), which tells the agent it cannot harvest credentials or content here — context the annotations do not carry.

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?

Three short sentences with zero waste, front-loading the return value before the safety and exclusion notes. Nothing is padded or restated from the title.

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 zero-param, read-only identity lookup with no output schema, the description covers what is returned and what is deliberately not returned. It stops short of naming the actual response field or confirming the auth precondition, but an agent has enough to call it correctly.

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?

The tool takes zero parameters, so the baseline is 4; there is nothing for the description to disambiguate. It correctly signals a no-argument call by not mentioning any inputs.

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?

States a specific verb and resource: returning the stable Browse Bridge user id for the signed-in account. This clearly separates it from browser_list_sessions and browser_get_status, which deal with sessions and status rather than account identity.

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?

Usage is implied — call it when you need the account's identity — but no sibling is named as an alternative and no prerequisite (e.g., must be signed in / a live control session) is stated. The negative disclosure ('does not return email, tokens, cookies, or page content') gives partial 'when not to use this' guidance by ruling out credential or content retrieval.

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