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 covered. The description still adds real context beyond them: the slot is only held temporarily (hold_expires_at), confirmation happens on payment, and the idempotency key is specified (same email, package and time returns the same pre-booking). It stops short of describing failure/expiry outcomes, so not a 5.

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 purpose, then preconditions, then payment and pricing guidance; every sentence carries operational information. It is dense and multi-topic, but nothing is padding.

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 an 11-parameter write tool with no output schema and no failure semantics, the description covers preconditions, payment routing, hold behavior, vouchers and idempotency. It could still say what the caller receives (booking reference, hold_expires_at) or what happens if the hold lapses.

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 the baseline is 3, but the description adds policy meaning not in the schema: MB WAY is preferred for instant payment and Multibanco is only valid >48 h out, and it frames extras/make-up as upsells. It largely repeats enum pricing already documented in the schema, which caps it 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 (pre-books), the resources it covers (portrait, family session, studio rental), the slot source (get_studio_slots), and the side effect (starts payment). An agent can distinguish it from siblings like get_studio_slots or request_quote 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?

Explicit precondition: 'Only call after the user has explicitly confirmed the package, the exact start time and their contact details.' It also gives alternatives and their constraints (suggest MB WAY first; Multibanco only for sessions >48 h away), which is exactly the when/when-not guidance an agent needs.

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