AI agents use add_tags to create or update resources in Obsidian MCP Server — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Obsidian MCP Server environment.
Adding tags modifies note metadata in a way that is reversible (tags can be removed), making this a Write category tool rather than Read or Destructive. Severity is medium because unintended tag additions could clutter a knowledge base, pollute search/filtering, or alter organizational structure, but the impact is limited in scope and easily recoverable compared to deletion or financial operations.
From the tool's definition Tool is named 'add_tags' and described as 'Add tags to an existing note' — it modifies metadata on an existing note by appending or creating tag associations, which is a reversible write operation.
Documented attack patterns abuse exactly the kind of access add_tags gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Obsidian MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for add_tags:
{
"version": "1",
"default": "deny",
"tools": {
"add_tags": {
"limits": [
{
"counter": "add_tags_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}add_tags 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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Add tags to an existing note. It is categorised as a Write tool in the Obsidian MCP Server MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Obsidian MCP Server MCP server in PolicyLayer and add a rule for add_tags: 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 Obsidian MCP Server. Nothing to install.
add_tags 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_tags 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_tags. 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_tags is provided by the Obsidian MCP Server MCP server (kynlos/obsidian-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Obsidian MCP Server, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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120 Obsidian MCP Server tools catalogued and risk-classified — across an index of 43,000+ MCP servers.