// MCP TOOL REFERENCE

prompt_start

Send a prompt to an active ACP session. Returns immediately with { status: "prompted" }. Use prompt or prompt_events to consume events.

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

mcacp Execute Risk 3/5

// WHEN AI AGENTS USE THIS TOOL

AI agents invoke prompt_start to trigger processes or run actions in Mcacp. 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.

// WHY ENFORCE A POLICY ON PROMPT_START

prompt_start can trigger processes with real-world consequences. An uncontrolled agent might start dozens of builds, send mass notifications, or kick off expensive compute jobs. Intercept enforces rate limits and validates arguments to keep execution within safe bounds.

// RECOMMENDED POLICY

Execute tools trigger processes. Rate-limit and validate arguments to prevent unintended side effects.

io-github-oortonaut-mcacp.yaml

tools:
  prompt_start:
    rules:
      - action: allow
        rate_limit:
          max: 10
          window: 60
        validate:
          required_args: true

See the full Mcacp policy for all 24 tools.

// DETAILS

Tool Name prompt_start

Category Execute

MCP Server Mcacp MCP Server

Risk Level High

// MORE MCACP TOOLS

Destructive agent_uninstall Destructive cancel Execute initialize Execute new_session Write agent_install Write close_session Write discover_agents Write request_permission

View all 24 tools →

// WHAT CAN GO WRONG

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

Browse the full MCP Attack Database →

// OTHER EXECUTE TOOLS ACROSS MCP SERVERS

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

Agent Passport System — Cryptographic Identity for AI Agents commerce_preflight Agent Passport System — Cryptographic Identity for AI Agents execute_with_context Agent Passport System — Cryptographic Identity for AI Agents gateway_execute_approval Agent Passport System — Cryptographic Identity for AI Agents governance_360 Agent Passport System — Cryptographic Identity for AI Agents parse_governance_block_html AgentClear — API Marketplace for AI Agents call_service

// IN CONTEXT OF HIGH RISK

prompt_start is one of the high-risk operations in Mcacp. For the full severity-focused view — only the high-risk tools with their recommended policies — see the breakdown for this server, or browse all high-risk tools across every MCP server.

// RELATED READING

// FAQ

What does the prompt_start tool do? +

Send a prompt to an active ACP session. Returns immediately with { status: "prompted" }. Use prompt or prompt_events to consume events.. It is categorised as a Execute tool in the Mcacp MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on prompt_start? +

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

What risk level is prompt_start? +

prompt_start is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.

Can I rate-limit prompt_start? +

Yes. Add a rate_limit block to the prompt_start 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 prompt_start completely? +

Set action: deny in the Intercept policy for prompt_start. 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 prompt_start? +

prompt_start is provided by the Mcacp MCP server (mcacp). Intercept sits as a proxy in front of this server to enforce policies before tool calls reach the server.

prompt_start

Enforce policies on Mcacp