Add a tag to a transaction, preserving any tags already on it. Args: transaction_id: The ID of the transaction tag_id: The tag ID to add
AI agents use add_transaction_tag to create or update resources in Monarch — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Monarch environment.
This is a Write operation because it creates or modifies data reversibly—adding a tag to a transaction is a reversible modification that does not delete data or execute arbitrary code. The blast radius is medium because incorrect tag application could cause transaction miscategorization or confusion, but the change is easily corrected.
From the tool's definition The tool description states it will 'Add a tag to a transaction', which modifies transaction metadata. The parameters (transaction_id, tag_id) confirm it targets a specific transaction and applies a change to it.
Documented attack patterns abuse exactly the kind of access add_transaction_tag gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Monarch, and nothing reaches the server without passing your rules. This is the rule we recommend for add_transaction_tag:
{
"version": "1",
"default": "deny",
"tools": {
"add_transaction_tag": {
"limits": [
{
"counter": "add_transaction_tag_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}add_transaction_tag 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.
Free to start. No card required.
Add a tag to a transaction, preserving any tags already on it. Args: transaction_id: The ID of the transaction tag_id: The tag ID to add. It is categorised as a Write tool in the Monarch MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Monarch MCP server in PolicyLayer and add a rule for add_transaction_tag: 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 Monarch. Nothing to install.
add_transaction_tag 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 add_transaction_tag 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 add_transaction_tag. 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.
add_transaction_tag is provided by the Monarch MCP server (robcerda/monarch-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 50 Monarch tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
Free to start. No card required.
50 Monarch tools catalogued and risk-classified — across an index of 42,500+ MCP servers.