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

Annotations already declare idempotentHint=true and destructiveHint=false, so the safety profile is partly covered. The description adds genuinely non-derivable context: a precondition state, a per-call platform fee (CHF 0.03 per accepted call), and a mandatory quote-before-book workflow. It stops short of explaining failure behavior or what happens if the slot is taken.

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 tight sentences, front-loaded with the action, then the precondition, then the exclusion and payment mechanics. The telegraphic 'Never:' fragment is compact but slightly clipped; no filler is present.

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 non-idempotent-looking mutation that moves money, the description covers the state precondition, the quote handshake, the fee, and idempotency semantics. With no output schema and 80% parameter coverage, the remaining gap is mainly not_before semantics and failure handling.

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 80%, so the schema already documents flow_id, quote_id, mandate_token and idempotency_key. The description reinforces the ordering of quote_id/mandate_token/idempotency_key but says nothing about not_before, which sits in tension with 'books the earliest free slot'. Baseline 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?

States a specific verb and resource with scope: 'Books the earliest free slot in the business's working windows.' Combined with the precondition ('Needs state ASSIGNED') and the quote-first requirement, an agent can distinguish this from siblings like quote, assign, or payment_collect 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?

Gives explicit prerequisites ('Needs state ASSIGNED'), an explicit exclusion ('Never: Use the agent's calendar as the source'), and the required call ordering ('quote first, then send quote_id, mandate_token and idempotency_key'). It does not name a specific alternative sibling tool for the excluded case, which keeps it short of a 5.

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