Tools: Custom fields
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 |
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
{
"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
curl -X POST https://api.tandemcrm.app/v1/ops/set_custom_fields \
-H "Authorization: Bearer $TANDEM_API_KEY" \
-H "Content-Type: application/json" \
-H "Idempotency-Key: log-call-acme-2026-11-02" \
-d '{"type":"company","id":"00000000-0000-4000-8000-000000000000","fields":{}}'
Input schema
The JSON Schema the MCP server advertises for this tool (over MCP it also accepts idempotency_key):
{
"$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"
]
}