i need a hook that calls before my mcp tools are being called. i would like to validate something before making mcp tool call.

Thanks for reaching out, Aman. I'm an AI assistant and I'm here to help. Give me a moment while I research this topic.

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Thanks — I read that as “okay.” I can proceed with concrete examples and steps. Quick confirmation so I pick the right approach: • Are your MCP tools hosted on an external MCP server, or are they invoked inside your agent process? • Which language/runtime is your agent or MCP server written in (Node.js, Go, Python, etc.)? • Do you need validation to block the call when it fails, or just to log/notify and let the call continue? If you want me to pick a common scenario and provide code, I can: • Show an agent-side wrapper example (Node.js or Go) that validates using

RunContext

and only forwards to the MCP tool on success, or • Show an MCP-server request handler (Node.js example) that validates incoming requests before executing the tool. Tell me which you'd prefer (or answer the three quick questions) and I’ll provide a ready-to-use example.

i'm using self hosted mcp server urls like google calendar and don't have flexiblity to add validation. now to run validate before that

Thanks — that’s helpful. Since you can’t add validation on the external MCP servers (e.g., Google Calendar), the right place to run validation is on the agent/client side before you call those MCP tool endpoints. I’ll outline the recommended approaches and give a simple, ready-to-adapt pattern you can drop into your agent. If you tell me your runtime (Node.js, Go, Python, etc.), I’ll provide a concrete code sample. What to do (high level) • Intercept/wrap the MCP tool call in your agent: Add a validation step in the code path that prepares or dispatches requests to the external MCP URL. If validation fails, do not call the external MCP endpoint. This is the most reliable and immediate option. • Use RunContext or request metadata where available: If your agent framework exposes a

RunContext

(or similar) with session/metadata, read needed info there for validation before forwarding the call. • Implement a small middleware or validator function so the approach is reusable and centralized. Simple, language-agnostic pattern 1. Centralize MCP calls behind a single function or service (e.g.,

callMcpTool(toolName, payload, ctx)

). 2. Before sending the HTTP request to the MCP URL, run `validate(toolName, payload, ctx)`: ◦ If validation returns success, proceed to call the MCP server. ◦ If validation fails, return an error or a controlled response back to your agent logic. 1. Log or emit events on validation failure for observability and debugging. Things to consider for validation • Synchronous blocking vs. non-blocking: For blocking validation, reject calls immediately on failure. For non-blocking, you can call the MCP tool but also surface warnings or run a compensating action later. • Timeouts and retries: Keep validation fast so you don't add significant latency; enforce timeouts on both validation and the external MCP call. • Security: Validate both request payloads and any authorization tokens before forwarding to the external MCP endpoint. • Auditing: Record which calls were blocked and why for later analysis. If you want a concrete example • Tell me your runtime: Node.js, Go, Python, or another. • Tell me whether you want the agent to return an error on validation failure or handle it differently (e.g., return a default response, queue for manual review). Once you tell me the language and desired failure behavior, I’ll provide a direct code example you can copy and use.

how to guarantee that

callMcpTool will happen always?

Thanks — I see you want to guarantee that your

callMcpTool

always runs (after your validation) so external MCP endpoints like Google Calendar are reliably invoked. I’ll outline a robust, practical approach you can apply in any runtime, then offer small examples for Node.js, Go, and Python. Before I give a concrete snippet, please confirm your runtime and whether you want strict guarantees (block until success with retries) or eventual‑delivery (enqueue and retry in background). High‑level strategy to guarantee execution • Centralize calls: Put every MCP invocation behind a single API or service function (your

callMcpTool

). This prevents ad hoc calls that skip validation or reliability logic. • Synchronous validation gate: Run validation first; only allow

callMcpTool

to proceed when validation passes. • Retry with backoff: On transient failures (network, 5xx), retry the MCP call with exponential backoff and a max attempts limit. • Durable queue for failures: If retries exhaust or you prefer not to block the user, write the call to a durable queue (database table, Redis stream, or message broker) for guaranteed background processing and retries. • Idempotency: Add an idempotency key per logical operation so retries or background processing won’t create duplicate side effects at the external MCP. • Observability & alerts: Log each attempt, outcome, and queue status; emit metrics and alerts for repeated failures. • Timeouts & circuit breaking: Use sensible timeouts and a circuit breaker to avoid cascading failures to your system if the external MCP is down. • Transactional coordination (if needed): For multi-step operations where the MCP call must follow other changes, use a transactionally consistent pattern (e.g., write a DB row marking intent + enqueue) so intent is durable before returning success to users. Concrete patterns (pick one or combine) • Synchronous with retries: Validate -> call

callMcpTool

-> retry on transient errors -> return final success/failure to caller. • Async guaranteed delivery: Validate -> persist intent in DB or enqueue message -> return accepted to caller -> background worker consumes queue and calls

callMcpTool

with retries & idempotency. • Hybrid: Attempt a few quick retries synchronously; if still failing, enqueue for background retry and return an “accepted, will retry” response. Quick examples Node.js / TypeScript (conceptual)

async function handler(req, res) {
  const payload = req.body;
  if (!validate(payload)) return res.status(400).send({error: 'validation failed'});

  try {
    await callMcpToolWithRetries(payload);
    return res.status(200).send({status: 'ok'});
  } catch (err) {
    // persist intent for background processing
    await enqueueFailedCall(payload);
    return res.status(202).send({status: 'queued_for_retry'});
  }
}

async function callMcpToolWithRetries(payload) {
  const maxAttempts = 5;
  for (let attempt = 1; attempt <= maxAttempts; attempt++) {
    try {
      return await callMcpTool(payload); // actual HTTP call to MCP URL
    } catch (err) {
      if (!isTransient(err) || attempt === maxAttempts) throw err;
      await sleep(backoff(attempt));
    }
  }
}

Go (conceptual)

if !validate(payload) {
  http.Error(w, "validation failed", http.StatusBadRequest)
  return
}
err := CallWithRetries(payload, 5)
if err != nil {
  EnqueueForRetry(payload)
  w.WriteHeader(http.StatusAccepted)
  return
}
w.WriteHeader(http.StatusOK)

Python (conceptual)

if not validate(payload):
    return jsonify(error="validation failed"), 400

try:
    call_with_retries(payload, max_attempts=5)
    return jsonify(status="ok"), 200
except Exception:
    enqueue_payload(payload)
    return jsonify(status="queued_for_retry"), 202

Idempotency and durable storage • Include an

operation_id

when creating the request. • Store operation rows with status: pending -> in_progress -> done / failed. • Background worker marks status changes so you can resume interrupted work. Questions so I can give a copy‑paste solution 1. Which runtime do you use (Node.js/TS, Go, Python, other)? 2. Do you want synchronous blocking until success (with retries) or are you okay with returning immediately and retrying in background? 3. Do you already have a queue or database I should target for examples (Postgres, Redis, RabbitMQ, SQS)? Tell me those and I’ll produce a full example (including idempotency key handling and a background worker) tailored to your stack.