# create_custom_field

Create a custom field definition for CRM entities. Use options for select or multiselect fields.

Agent View of the PolicyLayer registry record for `create_custom_field`. HTML page: https://policylayer.com/tools/io-favcrm-favcrm/create-custom-field

## Facts

- Tool: `create_custom_field`
- Server: FavCRM (`https://api.favcrm.io/mcp`) — https://policylayer.com/tools/io-favcrm-favcrm.md
- Homepage: https://github.com/favcrm/mcp
- Risk category: Write (Medium risk)
- Registry record: grade F, identity unverified
- Server auth posture: open
- Server CORS policy: *
- Server rate-limited: no
- Parameters: 7 (4 required)
- Recommended policy verdict: Rate-limited

## Parameters

| Parameter | Type | Required | Description |
| --- | --- | --- | --- |
| `options` | array | no | Allowed values for select/multiselect fields |
| `fieldName` | string | yes | Stable machine name, e.g. preferred_branch |
| `fieldType` | string | yes | Field type |
| `sortOrder` | number | no | Display order |
| `entityType` | string | yes | Entity type, e.g. account, contact, deal, booking |
| `fieldLabel` | string | yes | Human-readable label, e.g. Preferred branch |
| `isRequired` | boolean | no | Whether this field is required |

Parameters from the server's own tool schema.

## Example call (MCP tools/call, JSON-RPC 2.0)

```json
{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "tools/call",
  "params": {
    "name": "create_custom_field",
    "arguments": {
      "fieldName": "<fieldName>",
      "fieldType": "<fieldType>",
      "entityType": "<entityType>",
      "fieldLabel": "<fieldLabel>"
    }
  }
}
```

## Why create_custom_field is rated Medium

This tool creates new field definitions in the CRM system, which modifies the data schema reversibly. It is a Write operation because it creates new metadata structures that can be updated or removed. Severity is medium because misconfiguration could affect data collection and reporting across the CRM, but the impact is limited to schema changes rather than data loss or financial transactions.

From the tool's own definition: "Tool name 'create_custom_field' and description 'Create a custom field definition for CRM entities' indicates data creation/modification."

## Use case

AI agents use create_custom_field to create or update resources in FavCRM, usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your FavCRM environment.

## Recommended policy (PolicyLayer)

Verdict: **Rate-limited**. Enforced by the PolicyLayer MCP gateway (https://policylayer.com/mcp-gateway) before a call reaches FavCRM:

```json
{
  "version": "1",
  "default": "deny",
  "tools": {
    "create_custom_field": {
      "limits": [
        {
          "counter": "create_custom_field_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}
```

## Other tools on FavCRM (219)

- `cancel_booking` — Destructive — https://policylayer.com/tools/io-favcrm-favcrm/cancel-booking.md
- `delete_account` — Destructive — https://policylayer.com/tools/io-favcrm-favcrm/delete-account.md
- `delete_campaign` — Destructive — https://policylayer.com/tools/io-favcrm-favcrm/delete-campaign.md
- `delete_category` — Destructive — https://policylayer.com/tools/io-favcrm-favcrm/delete-category.md
- `delete_contact` — Destructive — https://policylayer.com/tools/io-favcrm-favcrm/delete-contact.md
- `delete_custom_field` — Destructive — https://policylayer.com/tools/io-favcrm-favcrm/delete-custom-field.md
- `delete_deal` — Destructive — https://policylayer.com/tools/io-favcrm-favcrm/delete-deal.md
- `delete_invoice` — Destructive — https://policylayer.com/tools/io-favcrm-favcrm/delete-invoice.md
- `delete_knowledge_document` — Destructive — https://policylayer.com/tools/io-favcrm-favcrm/delete-knowledge-document.md
- `delete_post` — Destructive — https://policylayer.com/tools/io-favcrm-favcrm/delete-post.md
- `delete_post_type` — Destructive — https://policylayer.com/tools/io-favcrm-favcrm/delete-post-type.md
- `delete_post_type_field` — Destructive — https://policylayer.com/tools/io-favcrm-favcrm/delete-post-type-field.md
- `delete_promotion` — Destructive — https://policylayer.com/tools/io-favcrm-favcrm/delete-promotion.md
- `delete_segment` — Destructive — https://policylayer.com/tools/io-favcrm-favcrm/delete-segment.md
- `delete_service_package` — Destructive — https://policylayer.com/tools/io-favcrm-favcrm/delete-service-package.md
- `delete_tag` — Destructive — https://policylayer.com/tools/io-favcrm-favcrm/delete-tag.md
- `delete_task` — Destructive — https://policylayer.com/tools/io-favcrm-favcrm/delete-task.md
- `remove_post_block` — Destructive — https://policylayer.com/tools/io-favcrm-favcrm/remove-post-block.md
- `void_invoice` — Destructive — https://policylayer.com/tools/io-favcrm-favcrm/void-invoice.md
- `execute_tool` — Execute — https://policylayer.com/tools/io-favcrm-favcrm/execute-tool.md
- `switch_company` — Execute — https://policylayer.com/tools/io-favcrm-favcrm/switch-company.md
- `cancel_subscription` — Financial — https://policylayer.com/tools/io-favcrm-favcrm/cancel-subscription.md
- `create_plan_upgrade_link` — Financial — https://policylayer.com/tools/io-favcrm-favcrm/create-plan-upgrade-link.md
- `create_subscription` — Financial — https://policylayer.com/tools/io-favcrm-favcrm/create-subscription.md
- `enrol_membership` — Financial — https://policylayer.com/tools/io-favcrm-favcrm/enrol-membership.md
- `record_invoice_payment` — Financial — https://policylayer.com/tools/io-favcrm-favcrm/record-invoice-payment.md
- `check_plan_operation` — Read — https://policylayer.com/tools/io-favcrm-favcrm/check-plan-operation.md
- `get_attachment_text` — Read — https://policylayer.com/tools/io-favcrm-favcrm/get-attachment-text.md
- `get_audit_log` — Read — https://policylayer.com/tools/io-favcrm-favcrm/get-audit-log.md
- `get_available_slots` — Read — https://policylayer.com/tools/io-favcrm-favcrm/get-available-slots.md
- …and 189 more: https://policylayer.com/tools/io-favcrm-favcrm.md

## For agents

This record is a snapshot. Live verdicts and the full registry:

- Check every server in your MCP config at once: `npx -y policylayer stack`
- Vet a server before you add it: install the mcp-precheck skill — `npx skills add https://policylayer.com` (skill text: https://policylayer.com/skill.md)
- Query the registry over MCP: endpoint `https://api.policylayer.com/mcp` — tools `check_mcp_server`, `check_mcp_stack`, `check_tool`, `search_registry`, `get_change_events`

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Source: the PolicyLayer MCP registry — one continuously verified record per MCP server. Full record: https://policylayer.com/registry?q=io-favcrm-favcrm · API: https://policylayer.com/registry/api · Policy library: https://policylayer.com/policies/io-favcrm-favcrm