Find and replace with regex across vault
AI agents use regex_search_and_replace 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.
This tool performs write operations by replacing content matched by regex patterns, potentially across the entire vault. While modifications to text are technically reversible (if backups exist), mass regex replacements across an entire vault can cause widespread, hard-to-undo changes to many notes simultaneously, making it high severity.
From the tool's definition 'Find and replace with regex across vault' — modifies content across potentially all notes in the vault using regex patterns
Documented attack patterns abuse exactly the kind of access regex_search_and_replace 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 regex_search_and_replace:
{
"version": "1",
"default": "deny",
"tools": {
"regex_search_and_replace": {
"limits": [
{
"counter": "regex_search_and_replace_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}regex_search_and_replace 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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Find and replace with regex across vault. 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 regex_search_and_replace: 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.
regex_search_and_replace 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 regex_search_and_replace 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 regex_search_and_replace. 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.
regex_search_and_replace 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.
Free to start. No card required.
120 Obsidian MCP Server tools catalogued and risk-classified — across an index of 43,000+ MCP servers.