# set_custom_fields

Set custom field values on one company, person or deal by id. Use the field keys and types from describe_schema; pass null to clear a field. Fields you don't mention are left alone.

| | |
| --- | --- |
| Group | Custom fields |
| Scope | `crm:write` |
| Who can call it | Agents and people with this scope. |
| Kind | Write. Recorded in the change history with who made it. |
| Retries | Pass `idempotency_key` (MCP) or the `Idempotency-Key` header (REST); a retry with the same key within 24 hours returns the first result. |
| Widget | In hosts that support MCP Apps, the result shows where the write landed (the changed record, the pipeline, or the updated list). |

## Parameters

| Parameter | Type | Required | Notes |
| --- | --- | --- | --- |
| `type` | `company` \\| `person` \\| `deal` | yes |  |
| `id` | id (uuid) | yes |  |
| `fields` | object | yes |  |
| `source` | object { name, url? } | no |  |
| `source.name` | string | yes | max 100 characters |
| `source.url` | string | no |  |

## Call it over MCP

```json
{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "tools/call",
  "params": {
    "name": "set_custom_fields",
    "arguments": {
      "type": "company",
      "id": "00000000-0000-4000-8000-000000000000",
      "fields": {},
      "idempotency_key": "log-call-acme-2026-11-02"
    }
  }
}
```

Send it to `https://api.tandemcrm.app/mcp` (streamable HTTP). Most people never write this by hand: their agent picks the tool from its description.

## Call it over REST

```bash
curl -X POST https://api.tandemcrm.app/v1/ops/set_custom_fields \
  -H "Authorization: Bearer $TANDEM_API_KEY" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: log-call-acme-2026-11-02" \
  -d '{"type":"company","id":"00000000-0000-4000-8000-000000000000","fields":{}}'
```

## Input schema

The JSON Schema the MCP server advertises for this tool (over MCP it also accepts `idempotency_key`):

```json
{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "type": "object",
  "properties": {
    "type": {
      "type": "string",
      "enum": [
        "company",
        "person",
        "deal"
      ]
    },
    "id": {
      "type": "string",
      "format": "uuid",
      "pattern": "^([0-9a-fA-F]{8}-[0-9a-fA-F]{4}-[1-8][0-9a-fA-F]{3}-[89abAB][0-9a-fA-F]{3}-[0-9a-fA-F]{12}|00000000-0000-0000-0000-000000000000|ffffffff-ffff-ffff-ffff-ffffffffffff)$"
    },
    "fields": {
      "type": "object",
      "propertyNames": {
        "type": "string"
      },
      "additionalProperties": {}
    },
    "source": {
      "type": "object",
      "properties": {
        "name": {
          "type": "string",
          "minLength": 1,
          "maxLength": 100
        },
        "url": {
          "type": "string",
          "pattern": "^https?:\\/\\/"
        }
      },
      "required": [
        "name"
      ]
    }
  },
  "required": [
    "type",
    "id",
    "fields"
  ]
}
```