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

Annotations only declare readOnlyHint=false and destructiveHint=false; the description adds materially more — a session token is required, the returned URL expires in ~20 minutes, and booking confirmation happens asynchronously via webhook rather than through a follow-up call. That is exactly the kind of side-effect and lifecycle information the annotations cannot 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?

Front-loaded with the core action and the recommended-use claim, and every sentence carries information (requirements, return values, follow-up behavior). It is a single dense paragraph with heavy inline backticks, so structure 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?

There is no output schema, and the description compensates by naming the returned fields (checkoutUrl, checkoutToken, message) and their lifetime. For a non-destructive mutation with a 5-parameter flat schema, the agent has everything needed to call it and interpret the result.

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 coverage is 100%, so baseline is 3, but the description adds real meaning: it identifies bookingId as the `preparedBookingId` from prepare_booking and pins sessionToken to guest_login. It also asserts a session is REQUIRED even though the schema labels sessionToken "Optional" — useful but a discrepancy the agent must resolve, which keeps this below 5.

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 ("Creates a hosted Revolut payment link") plus the precondition ("for a prepared booking"), and distinguishes itself from siblings by naming confirm_booking as B2B-only and positioning itself as the consumer payment path. An agent can separate it from get_payment_url and confirm_booking 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?

Explicitly scopes usage to "ordinary consumers (no credit line)" and marks itself as the RECOMMENDED route, which implies the credit-line alternative exists. It also gives a hard exclusion ("do not call `confirm_booking`, which is B2B-only") and a prerequisite workflow (prepare_booking then guest_login), so when-to-use and when-not-to-use are both covered.

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