Send an emoji reaction on a previously received/sent message. Pass empty string for
AI agents use send_reaction_message to create or update resources in Mcp Ap2 — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Mcp Ap2 environment.
The tool creates/appends a reaction to an existing message, which is a Write operation (reversible modification). Despite being on a payment protocol server, this specific tool performs a social/messaging action rather than a financial operation. No destructive, financial, or execute-level capabilities are evident. Severity is low because emoji reactions have minimal blast radius and are easily undone.
From the tool's definition Tool name is 'send_reaction_message' and description states 'Send an emoji reaction on a previously received/sent message.' This modifies message state by adding a reaction, which is a reversible write operation.
Documented attack patterns abuse exactly the kind of access send_reaction_message gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Mcp Ap2, and nothing reaches the server without passing your rules. This is the rule we recommend for send_reaction_message:
{
"version": "1",
"default": "deny",
"tools": {
"send_reaction_message": {
"limits": [
{
"counter": "send_reaction_message_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}send_reaction_message 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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Send an emoji reaction on a previously received/sent message. Pass empty string for. It is categorised as a Write tool in the Mcp Ap2 MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Mcp Ap2 MCP server in PolicyLayer and add a rule for send_reaction_message: 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 Mcp Ap2. Nothing to install.
send_reaction_message 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 send_reaction_message 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 send_reaction_message. 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.
send_reaction_message is provided by the Mcp Ap2 MCP server (@codespar/mcp-ap2). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Mcp Ap2, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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