update_frontmatter_field

THE RISK

Medium Risk

Why update_frontmatter_field needs a policy

This tool creates or modifies data reversibly by editing YAML frontmatter fields in Obsidian notes. It is a Write operation because it alters note properties (such as tags, dates, status fields, or custom metadata) without deleting content. The targeted edit approach ('without rewriting note') suggests surgical modification rather than destructive replacement.

From the tool's definition Tool name 'update_frontmatter_field' and description 'Edit specific YAML field without rewriting note' indicate modification of note metadata through targeted field updates.

Documented attack patterns abuse exactly the kind of access update_frontmatter_field gives an agent:

POLICY

How to control update_frontmatter_field

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 update_frontmatter_field:

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "update_frontmatter_field": {
      "limits": [
        {
          "counter": "update_frontmatter_field_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

update_frontmatter_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.

Create a free account and register Obsidian MCP Server — nothing to install.
Add this policy — paste it, or build it visually.
Point your MCP client (Claude, Cursor, anything) at your gateway URL.

LIMIT THIS TOOL →

Free to start. No card required.

EXPLORE

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Go deeper

The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Argument validation → Checking tool call arguments against schema and policy before they run.
Scoped token → Per-person credentials that grant a defined subset of servers and tools.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →

FAQ

Questions about update_frontmatter_field

What does the update_frontmatter_field tool do? +

Edit specific YAML field without rewriting 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.

How do I enforce a policy on update_frontmatter_field? +

Register the Obsidian MCP Server MCP server in PolicyLayer and add a rule for update_frontmatter_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 Obsidian MCP Server. Nothing to install.

What risk level is update_frontmatter_field? +

update_frontmatter_field is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.

Can I rate-limit update_frontmatter_field? +

Yes. Add a rate_limit block to the update_frontmatter_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.

How do I block update_frontmatter_field completely? +

Set action: deny in the PolicyLayer policy for update_frontmatter_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.

What MCP server provides update_frontmatter_field? +

update_frontmatter_field 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.

Enforce policy on every Obsidian MCP Server tool call.

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.

CHECK YOUR STACK →