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

The description discloses critical behavioral traits beyond the annotations: 'Nothing is reserved until the guest pays on that link (valid 24 hours)' clarifies the non-reserving nature, and 'Rate limited' warns of throttling. It also explains that guest name/email are used for confirmation. These details add significant value over the raw annotations (readOnlyHint=false, openWorldHint=true), which only hint at mutation and unknown side effects but don't specify the actual flow.

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 description is five sentences and covers purpose, timing, prerequisites, and rate limits in a logical order. It front-loads the main action and then adds constraints. While slightly longer than the minimal ideal, every sentence adds necessary information without fluff or repetition.

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 tool with 14 parameters and nested objects, the description covers the essential contextual aspects: when to use, what the output is (a secure checkout link), the fact that nothing is reserved until payment, and the prerequisite to confirm details. It does not describe the exact response format, but the phrase 'get a secure checkout link' implies the primary output. Given the rich schema descriptions, this is sufficiently complete for an agent 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?

Schema description coverage is 93%, so the input schema already documents most parameters with clear descriptions (e.g., 'Number of dogs', 'Arrival date, YYYY-MM-DD'). The description adds minimal parameter-specific meaning beyond saying guest name/email are required and used for confirmation, which is already reflected in the schema's required fields. Since the schema carries the burden, a baseline of 3 is appropriate.

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 clearly states the tool's purpose: 'Start a booking and get a secure checkout link for the guest.' This is a specific verb-resource pair and is unmistakably distinct from the sibling tools (check_availability, get_campsite, get_quote, search_campsites) which are all informational. No ambiguity about what action it performs.

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?

The description gives an explicit condition for use: 'Only works at campsites that take payment online (assistant_can_book is true); elsewhere send the guest to the booking_url to book themselves.' This directly tells the agent when to use this tool versus the alternative (directing the guest to the booking URL). It also instructs to 'Confirm every detail with the guest first,' which is a clear prerequisite. This is exemplary usage guidance.

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