Add, update, or remove a custom field on a contact
| Name | Required | Description | Default |
|---|---|---|---|
| id | No | The custom field ID (required for "update" and "remove") | |
| action | Yes | Action to perform | |
| contact_id | No | The contact ID (required for "add") | |
| field_name | No | Field name, e.g. "Favorite Color" (required for "add") | |
| field_group | No | Group to organize fields, e.g. "Preferences" | |
| field_value | No | Field value (required for "add") |
Changes observed during successful MCP inspections.
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations are provided, so the description carries the full burden of behavioral disclosure. It only restates the actions without explaining side effects (e.g., whether 'remove' is permanent, whether 'update' overwrites existing values), permissions needed, or impact on the contact. This is a significant gap for a mutation 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?
The description is a single, concise sentence that lists all actions. It is front-loaded and contains no filler. Every word 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?
This is a multi-action tool with 6 parameters, no output schema, and no annotations. The description is too sparse to be complete: it does not explain differences between actions, potential side effects, return values, or error conditions. The schema covers parameter requirements but not behavioral context, leaving the description insufficient for safe invocation.
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 baseline is 3. The description adds no extra meaning beyond the schema; it does not elaborate on parameter relationships or provide examples. The schema's conditional requirements (e.g., 'required for update/remove') are already documented, so the description neither helps nor hurts.
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 the tool's function: 'Add, update, or remove a custom field on a contact.' It uses a specific verb list (add/update/remove) and identifies the resource (custom field on a contact), distinguishing it from sibling tools like contact_update or contact_create.
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?
No guidance is provided on when to use this tool versus alternatives. The description does not mention exclusions, prerequisites, or scenarios where another tool (e.g., contact_update for standard fields) would be more appropriate. The schema hints at conditional requirements, but the description itself offers no usage context.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
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