create_a_contact_custom_field

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

The description explicitly states 'Not idempotent — calling twice may create duplicates', which adds behavioral info beyond the annotations (idempotentHint: false). It also labels the tool as 'WRITE'. However, it does not disclose other traits like authentication requirements, rate limits, or what happens if a field with the same title exists. Given annotations are present, the description adds moderate value.

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?

The description is very concise: a single header line with emoji and HTTP method, plus two short sentences. It front-loads the key information (create, not idempotent). However, it could be slightly more structured by separating the purpose from behavioral traits.

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?

Given no output schema, the description does not explain what the tool returns (e.g., the created field object or an ID). It also does not mention that this creates a contact-specific custom field, though the tool name implies it. For a creation tool with a nested input schema, the description is adequate but could be more complete by describing the response or linking to contact context.

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?

The input schema has 100% description coverage for all parameters, so the description does not need to add extra meaning. The tool description does not highlight required fields ('title' and 'type') or clarify the nested object structure. Baseline 3 is appropriate as the schema already covers parameter details.

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 clearly states 'Create a custom field' and uses verbs 'creates' with resource 'custom field'. The header 'WRITE · creates data · Fields' further distinguishes it from sibling tools like 'create_a_custom_field_group' or 'create_a_customfieldmeta'. The tool name explicitly includes 'contact_custom_field', making the purpose unambiguous.

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 provides no guidance on when to use this tool versus alternatives such as 'create_a_custom_field_group' or 'create_a_customfieldmeta'. It does not specify prerequisites, or situations where this tool should be avoided. No exclusions or alternative tool references are given.

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