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

Annotations already cover the safety profile (not read-only, open-world, non-idempotent, non-destructive), and the description adds substantial beyond-schema behavior: exact price and network, the x402 PAYMENT-SIGNATURE header requirement, the 402 challenge with amount 100000, the fact that in-session actions are unmetered, and that login/CAPTCHA and new origin permissions remain the user's responsibility. This is unusually rich disclosure for a paid mutation tool.

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?

Sentences are dense with no filler, and the cost/payment condition is front-loaded where an agent needs it before deciding. It is on the long side for a three-parameter tool, but every clause carries distinct operative information.

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 paid, non-idempotent mutation tool with no output schema, the description covers cost, payment mechanics, session semantics, and user responsibilities. The main gap is the return payload: it never says what a successful session object contains (session ID/token, expiry), which the agent needs to chain into session_action.

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 parameter meaning. It explains trusted_device_id well ('private 256-bit routing capability' so the extension can auto-claim), and 'origin-scoped' implicitly frames allowed_origins, but ttl_seconds is only gestured at with 'short-lived' and no parameter names or bounds are given. Partial compensation for a low-coverage schema.

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 with scope: 'Create a short-lived, origin-scoped browser delegation session.' That is far more precise than the sibling names alone (session_action, session_status) and implies the lifecycle position. It doesn't explicitly contrast with device_pairing_create or session_action, so it stops short of full sibling differentiation.

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 context is implied rather than stated: the agent learns payment is required and that a session can optionally be routed to an enrolled device, but there is no explicit 'use this instead of X when Y' routing against sibling tools like session_action or device_pairing_create. The prerequisites (payment header, user handling login/CAPTCHA) are present, which lifts it above bare minimum.

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