Place a raster or SVG image on the board at (x, y) with explicit width/height in board pixels. data_url MUST be a data:image/(png|jpeg|gif|webp|svg+xml);base64,... string ≤ ~900 kB; hosted URLs are not accepted. Strongly recommended: also pass a tiny thumb_data_url (≤8 kB JPEG/PNG/WebP, ~64 px on...
Risk signalsHigh parameter count (10 properties)
Part of the Cnvs App server.
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AI agents use add_image to create or modify resources in Cnvs App. Write operations carry medium risk because an autonomous agent could trigger bulk unintended modifications. Rate limits prevent a single agent session from making hundreds of changes in rapid succession. Argument validation ensures the agent passes expected values.
Without a policy, an AI agent could call add_image repeatedly, creating or modifying resources faster than any human could review. PolicyLayer's rate limiting ensures write operations happen at a controlled pace, and argument validation catches malformed or unexpected inputs before they reach Cnvs App.
Write tools can modify data. A rate limit prevents runaway bulk operations from AI agents.
{
"version": "1",
"default": "deny",
"tools": {
"add_image": {
"limits": [
{
"counter": "add_image_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}See the full Cnvs App policy for all 10 tools.
These attack patterns abuse exactly the kind of access add_image gives an agent. Each links to the full case and the policy that stops it:
Other write tools across the catalogue. The same approach applies to each: rate-limit and validate the arguments.
Place a raster or SVG image on the board at (x, y) with explicit width/height in board pixels. data_url MUST be a data:image/(png|jpeg|gif|webp|svg+xml);base64,... string ≤ ~900 kB; hosted URLs are not accepted. Strongly recommended: also pass a tiny thumb_data_url (≤8 kB JPEG/PNG/WebP, ~64 px on the long edge) — it is embedded into the SVG preview so OTHER AI viewers (and you, on later get_preview calls) can actually see the image instead of a placeholder box.. It is categorised as a Write tool in the Cnvs App MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Cnvs App MCP server in PolicyLayer and add a rule for add_image: 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.
add_image 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 add_image 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 add_image. 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.
add_image 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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