Long-poll: blocks until the next edit lands on this board, then returns. WHEN TO CALL THIS: if your MCP client does NOT surface notifications/resources/updated events from resources/subscribe back to the model (most chat clients do not — they receive the SSE event but don't inject it into your co...
Part of the Cnvs App server.
Free to start. No card required.
AI agents invoke wait_for_update to trigger processes or run actions in Cnvs App. Execute operations can have side effects beyond the immediate call -- triggering builds, sending notifications, or starting workflows. Rate limits and argument validation are essential to prevent runaway execution.
wait_for_update can trigger processes with real-world consequences. An uncontrolled agent might start dozens of builds, send mass notifications, or kick off expensive compute jobs. PolicyLayer enforces rate limits and validates arguments to keep execution within safe bounds.
Execute tools trigger processes. Rate-limit and validate arguments to prevent unintended side effects.
{
"version": "1",
"default": "deny",
"tools": {
"wait_for_update": {
"limits": [
{
"counter": "wait_for_update_rate",
"window": "minute",
"max": 10,
"scope": "grant"
}
]
}
}
}See the full Cnvs App policy for all 10 tools.
These attack patterns abuse exactly the kind of access wait_for_update gives an agent. Each links to the full case and the policy that stops it:
Other execute tools across the catalogue. The same approach applies to each: rate-limit and validate the arguments.
Long-poll: blocks until the next edit lands on this board, then returns. WHEN TO CALL THIS: if your MCP client does NOT surface notifications/resources/updated events from resources/subscribe back to the model (most chat clients do not — they receive the SSE event but don't inject it into your context), this tool is how you 'wait for the human' inside a single turn. Typical flow: you draw / write what you were asked to, then instead of ending your turn you call wait_for_update(board_id). When the human adds, moves, or erases something, the call returns and you refresh with get_preview / get_board and continue the collaboration. Great for turn-based interactions (games like tic-tac-toe, brainstorming where you respond to each sticky the user drops, sketch-and-feedback loops, etc.). If your client DOES deliver resource notifications natively, prefer resources/subscribe — it's cheaper and has no timeout ceiling. BEHAVIOUR: resolves ~3 s after the edit burst settles (same debounce as the push notifications — this is intentional so drags and long strokes collapse into one wake-up). Returns { updated: true, timedOut: false } on a real edit, or { updated: false, timedOut: true } if nothing happened within timeout_ms. On timeout, just call it again to keep waiting; chaining calls is cheap. timeout_ms is clamped to [1000, 55000]; default 25000 (leaves headroom under typical 60 s proxy timeouts).. It is categorised as a Execute tool in the Cnvs App MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.
Register the Cnvs App MCP server in PolicyLayer and add a rule for wait_for_update: 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.
wait_for_update is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.
Yes. Add a rate_limit block to the wait_for_update 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 wait_for_update. 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.
wait_for_update 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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4,600+ MCP servers and 31,000+ tools scanned and risk-classified.