AI agents use update_canvas_card 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 creates or modifies data reversibly by updating canvas cards. It does not irreversibly delete (Destructive), execute arbitrary code (Execute), or trigger financial operations (Financial). While it modifies state, the changes are reversible through undo or subsequent updates, placing it squarely in the Write category.
From the tool's definition Tool name 'update_canvas_card' and description 'Modify existing canvas card' indicate modification of existing data structures within Obsidian canvas elements.
Documented attack patterns abuse exactly the kind of access update_canvas_card 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 update_canvas_card:
{
"version": "1",
"default": "deny",
"tools": {
"update_canvas_card": {
"limits": [
{
"counter": "update_canvas_card_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}update_canvas_card 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.
Modify existing canvas card. 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 update_canvas_card: 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.
update_canvas_card 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 update_canvas_card 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 update_canvas_card. 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.
update_canvas_card 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.