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

Annotations already declare the write profile (readOnlyHint=false, destructiveHint=false, idempotentHint=false). The description adds useful conditional behavior — relationship requires target_object, select/multiselect need options — and notes it returns the created field definition. However it omits auth requirements, uniqueness/failure behavior, and idempotency nuance beyond the annotation.

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 the core action, then 'When to use' and a concrete example, which is good structure. The inline enumeration of every field_type value is somewhat redundant with the schema enum, a minor waste rather than a serious flaw.

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?

With an output schema present, return values need no explanation, and the description covers field types, the relationship special case, options, a usage trigger, and a worked example. It is complete enough to call correctly, though it leaves creation constraints (slug uniqueness, permissions) implicit.

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 of the 5 parameters is already documented in the schema. The description restates field_type values and the target_object/options conditions, which only reinforces what the schema provides rather than adding new semantics. 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+resource ('Add a custom field') and scopes the target ('any object that supports them — core objects with custom fields, or any custom object'). An agent can distinguish it from update_field, archive_field, and define_object without opening a 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?

The explicit 'When to use' line names the trigger (an admin wants a new attribute on a core or custom object) and enumerates the field flavors. It gives clear context but names no alternative (e.g., update_field for modifying an existing field) and states no exclusions, so it stops 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.