Draw a freehand stroke on the board. Use for arrows, underlines, connector lines, annotations, or simple shapes — a straight line needs two points, a rough circle wants ~20. Stroke width is fixed at 3 px; color accepts any CSS color (e.g. '#ff0000', 'var(--text-color)'). Accepts three equivalent ...
Part of the Cnvs App server.
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AI agents may call draw_stroke to permanently remove or destroy resources in Cnvs App. Without a policy, an autonomous agent could delete critical data in a loop with no way to undo the damage. PolicyLayer blocks destructive tools by default and requires explicit human approval before enabling them.
Without a policy, an AI agent could call draw_stroke in a loop, permanently destroying resources in Cnvs App. There is no undo for destructive operations. PolicyLayer blocks this tool by default and only allows it when a human explicitly approves the action.
Destructive tools permanently remove data. Block by default. Only enable with explicit approval workflows.
{
"version": "1",
"default": "deny",
"hide": [
"draw_stroke"
]
}See the full Cnvs App policy for all 10 tools.
These attack patterns abuse exactly the kind of access draw_stroke gives an agent. Each links to the full case and the policy that stops it:
Other destructive tools across the catalogue. The same approach applies to each: deny by default, or require human approval.
Draw a freehand stroke on the board. Use for arrows, underlines, connector lines, annotations, or simple shapes — a straight line needs two points, a rough circle wants ~20. Stroke width is fixed at 3 px; color accepts any CSS color (e.g. '#ff0000', 'var(--text-color)'). Accepts three equivalent point formats — pick whichever your MCP client serialises cleanly: nested [[x,y],[x,y],...], flat [x1,y1,x2,y2,...], or a JSON string of either. Some clients (Claude Code as of 2026-04) drop nested arrays during tool-call serialisation, so prefer the flat form or the JSON-string form when in doubt. To delete a stroke later, use erase with kind: 'line' and the id returned here.. It is categorised as a Destructive tool in the Cnvs App MCP Server, which means it can permanently delete or destroy data. Block by default and require explicit approval.
Register the Cnvs App MCP server in PolicyLayer and add a rule for draw_stroke: 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 Cnvs App. Nothing to install.
draw_stroke is a Destructive tool with critical risk. Critical-risk tools should be blocked by default and only enabled with explicit human approval.
Yes. Add a rate_limit block to the draw_stroke 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 draw_stroke. 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.
draw_stroke is provided by the Cnvs App MCP server (https://cnvs.app/mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 10 Cnvs App tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
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