AI agents use create_field to create or update resources in Tana MCP Server — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Tana MCP Server environment.
The tool creates new field definitions, which is a write operation that modifies workspace schema but does not delete data or execute arbitrary code. Creation of fields is reversible (fields can be deleted/modified later), making it Write rather than Destructive.
From the tool's definition Tool name 'create_field' and description 'Create a new field definition in Tana' indicate creation of new metadata/schema elements in the workspace. This is a reversible write operation that modifies the structure of the workspace.
Documented attack patterns abuse exactly the kind of access create_field gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Tana MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for create_field:
{
"version": "1",
"default": "deny",
"tools": {
"create_field": {
"limits": [
{
"counter": "create_field_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}create_field 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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Create a new field definition in Tana. It is categorised as a Write tool in the Tana MCP Server MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Tana MCP Server MCP server in PolicyLayer and add a rule for create_field: 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 Tana MCP Server. Nothing to install.
create_field 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 create_field 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 create_field. 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.
create_field is provided by the Tana MCP Server MCP server (tim-mcdonnell/tana-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 12 Tana MCP Server tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
Free to start. No card required.
12 Tana MCP Server tools catalogued and risk-classified — across an index of 42,500+ MCP servers.