List custom fields

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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is known. The description adds useful behavior beyond annotations by explaining that the output is a set of definitions scoped to a location, filterable by model, and that returned IDs are meant to be reused in read/write operations on custom field values. It does not mention pagination or limits, but that is a minor gap for a simple list tool.

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?

Two tight sentences with no filler. The action and resource are front-loaded, followed by the filter guidance and the downstream usage hint. 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 tool with only two parameters, no required inputs, and full schema coverage, the description is nearly complete: it states what is listed, the filtering dimension, and how the returned IDs should be used. It does not describe the output structure or pagination, but the absence of an output schema and the simplicity of a list operation make this a minor omission rather than a critical gap.

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 the schema already fully documents both parameters, including the model enum and locationId default. The description adds only a light interpretation of 'model' ('which fields apply where') and restates 'location', without introducing new parameter-level meaning beyond the schema baseline.

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?

The description uses a specific verb and resource ('List custom field definitions for a location') and immediately clarifies the model filter scope. It is clearly distinct from the sibling ghl_get_custom_field by being a list operation, and the phrase 'which fields apply where' adds functional differentiation.

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 description gives concrete guidance on using the model parameter ('Filter by model ... to see which fields apply where') and explains the downstream purpose of the return value ('Use the returned ids when reading/writing custom field values on contacts'). It does not explicitly name alternatives like ghl_get_custom_field for single-field lookup, but the list-vs-get distinction is clear enough from context.

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