AI agents use lock_elements to create or update resources in Excalidraw — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Excalidraw environment.
Locking elements modifies their properties (read-only state) but does not create, delete, or irreversibly alter the actual diagram content. This is a reversible state change (unlock_elements can undo it), making it Write rather than Destructive.
From the tool's definition Tool name is 'lock_elements' paired with sibling 'unlock_elements' on an Excalidraw canvas manipulation server.
Documented attack patterns abuse exactly the kind of access lock_elements gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Excalidraw, and nothing reaches the server without passing your rules. This is the rule we recommend for lock_elements:
{
"version": "1",
"default": "deny",
"tools": {
"lock_elements": {
"limits": [
{
"counter": "lock_elements_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}lock_elements 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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lock_elements. It is categorised as a Write tool in the Excalidraw MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Excalidraw MCP server in PolicyLayer and add a rule for lock_elements: 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 Excalidraw. Nothing to install.
lock_elements 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 lock_elements 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 lock_elements. 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.
lock_elements is provided by the Excalidraw MCP server (lesleslie/excalidraw-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Excalidraw, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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17 Excalidraw tools catalogued and risk-classified — across an index of 43,000+ MCP servers.