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

The annotations already flag readOnlyHint=false, destructiveHint=true and openWorldHint=true, and the description adds real content on top: confirm gating, the no-email/completed behavior for past starts, the email sent for future starts, and the explicit "no money moves through the assistant" clarification of the pay-link side effect. It never explains why the operation is flagged destructive (e.g. overwriting an existing booking or overlapping sessions), which is the one behavioral gap.

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?

Five short sentences with no filler, and the most important semantics (preview-then-confirm, then side effects) are front-loaded. Slightly dense on the money/pay-link framing, but every sentence earns its place.

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 4-parameter mutation tool with no output schema, the description covers the confirmation contract and the email/side-effect outcomes well. It stops short of describing what the preview actually returns or what happens on conflicts, which the agent would need to interpret the preview call.

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 100%, so each parameter (start, confirm, client_id, service_id) is already documented in the schema with equivalent or greater detail. The description adds only marginal framing (the confirm gate, dashboard parity) rather than new parameter meaning, so the baseline 3 applies.

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?

"Book a client into a service at a start time, the same way the dashboard books" gives a precise verb (book), resource (session/service), and actor (client), and is immediately distinguishable from the sibling tools like cancel_booking, reschedule_booking and find_open_slots.

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 clearly states the preview-first workflow ("Returns a preview first and only acts when confirm=true") and the past-vs-future start distinction, which tells the agent when the write actually happens. It does not, however, name alternatives such as reschedule_booking for moving an existing booking or find_open_slots for slot discovery.

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