Post the necessary fields for the API to upload files. The files need to be a buffer with the key
AI agents use upload-to-custom-fields to create or update resources in GoHighLevel MCP Server — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your GoHighLevel MCP Server environment.
This tool creates or modifies custom field data by uploading files. While it involves file handling, the operation is reversible (files can be replaced or removed), and there is no explicit mention of deletion or irreversible destruction.
From the tool's definition The tool name 'upload-to-custom-fields' and description stating 'Post the necessary fields for the API to upload files' indicates a file upload operation that creates or modifies data. The phrase 'Post' is an HTTP method indicating data creation/modification.
Documented attack patterns abuse exactly the kind of access upload-to-custom-fields gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and GoHighLevel MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for upload-to-custom-fields:
{
"version": "1",
"default": "deny",
"tools": {
"upload-to-custom-fields": {
"limits": [
{
"counter": "upload-to-custom-fields_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}upload-to-custom-fields stays usable, but capped — an agent stuck in a loop can't make hundreds of changes a minute. Everything else on the server is denied unless you say otherwise.
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Post the necessary fields for the API to upload files. The files need to be a buffer with the key. It is categorised as a Write tool in the GoHighLevel MCP Server MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the GoHighLevel MCP Server MCP server in PolicyLayer and add a rule for upload-to-custom-fields: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches GoHighLevel MCP Server. Nothing to install.
upload-to-custom-fields is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.
Yes. Add a rate_limit block to the upload-to-custom-fields rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.
Set action: deny in the PolicyLayer policy for upload-to-custom-fields. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.
upload-to-custom-fields is provided by the GoHighLevel MCP Server MCP server (drausal/gohighlevel-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from GoHighLevel MCP Server, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
Free to start. No card required.
406 GoHighLevel MCP Server tools catalogued and risk-classified — across an index of 43,000+ MCP servers.