a2a_send_message

Send a message to an ERC-8004 agent via the A2A (Agent-to-Agent) protocol. The agent must have an A2A endpoint configured. Requires configured wallet. Returns a task ID for tracking the conversation.

Part of the Agent0 MCP server. Enforce policies on this tool with Intercept, the open-source MCP proxy.

@rickydata/agent0-mcp Write Risk 2/5

// WHEN AI AGENTS USE THIS TOOL

AI agents use a2a_send_message to create or modify resources in Agent0. 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.

// WHY ENFORCE A POLICY ON A2A_SEND_MESSAGE

Without a policy, an AI agent could call a2a_send_message repeatedly, creating or modifying resources faster than any human could review. Intercept's rate limiting ensures write operations happen at a controlled pace, and argument validation catches malformed or unexpected inputs before they reach Agent0.

// RECOMMENDED POLICY

Write tools can modify data. A rate limit prevents runaway bulk operations from AI agents.

agent0.yaml

tools:
  a2a_send_message:
    rules:
      - action: allow
        rate_limit:
          max: 30
          window: 60

See the full Agent0 policy for all 34 tools.

// DETAILS

Tool Name a2a_send_message

Category Write

MCP Server Agent0 MCP Server

Risk Level Medium

// MORE AGENT0 TOOLS

Financial transfer_agent Destructive a2a_cancel_task Destructive revoke_feedback Write a2a_task_message Write configure_wallet Write register_agent Write update_agent Read a2a_get_task

View all 34 tools →

// WHAT CAN GO WRONG

Agents calling write-class tools like a2a_send_message have been implicated in these attack patterns. Read the full case and prevention policy for each:

Browse the full MCP Attack Database →

// OTHER WRITE TOOLS ACROSS MCP SERVERS

Other tools in the Write risk category across the catalogue. The same policy patterns (rate-limit, validate) apply to each.

AbraFlexi contact_create AbraFlexi contact_update AbraFlexi evidence_create AbraFlexi evidence_update AbraFlexi invoice_issued_update AbraFlexi invoice_received_create

// RELATED READING

// FAQ

What does the a2a_send_message tool do? +

Send a message to an ERC-8004 agent via the A2A (Agent-to-Agent) protocol. The agent must have an A2A endpoint configured. Requires configured wallet. Returns a task ID for tracking the conversation.. It is categorised as a Write tool in the Agent0 MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on a2a_send_message? +

Add a rule in your Intercept YAML policy under the tools section for a2a_send_message. You can allow, deny, rate-limit, or validate arguments. Then run Intercept as a proxy in front of the Agent0 MCP server.

What risk level is a2a_send_message? +

a2a_send_message is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.

Can I rate-limit a2a_send_message? +

Yes. Add a rate_limit block to the a2a_send_message rule in your Intercept 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.

How do I block a2a_send_message completely? +

Set action: deny in the Intercept policy for a2a_send_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.

What MCP server provides a2a_send_message? +

a2a_send_message is provided by the Agent0 MCP server (@rickydata/agent0-mcp). Intercept sits as a proxy in front of this server to enforce policies before tool calls reach the server.

a2a_send_message

Enforce policies on Agent0