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

With no annotations, the description carries the full behavioral burden. It does disclose three useful traits: partial-update semantics ('send only the fields to update'), an immutable-field set (Id, BookingReference, BookingDate, MemberId), and auth handled via the x-api-key header. It says nothing about failure behavior on an invalid booking_ref, whether omitted fields are preserved, or what the response contains, which matters for a 21-parameter mutation.

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?

Four short sentences, front-loaded with the core action and the immutability constraint. The trailing API-key sentence is somewhat boilerplate but does convey that the caller need not supply auth, so it is not pure waste.

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 21-parameter mutation with no annotations and no output schema, the description covers the essentials (what changes, what cannot change, auth) but omits return behavior and any cross-field validation rules such as date ordering or entry/exit port consistency. It is adequate, not complete.

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; the description earns a point by adding a constraint the schema does not state, namely that BookingReference, BookingDate, MemberId and Id are not editable. However, the schema still exposes booking_ref and member_id as writable properties with no immutability note, and the PascalCase field names in the description do not match the snake_case schema keys, which creates avoidable ambiguity.

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 ('Updates one or more editable fields of an existing booking') and adds scope detail by enumerating the immutable fields. It is clearly a mutation of an existing entity, distinguishable from create_booking, though it never names that sibling explicitly.

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?

Usage is implied: use this to modify an existing booking, and send only changed fields. There is no explicit when-not guidance (e.g., use get_booking to read, create_booking to create) and no note on when to prefer other sibling tools.

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