denoland/deno · error · Error

ERR_INSPECTOR_NOT_ACTIVE

ERR_INSPECTOR_NOT_ACTIVE

Error message

Inspector is not active

What it means

inspector.waitForDebugger() suspends the current thread until an attached debugger resumes it. It is only valid while the inspector is active: the underlying op_inspector_wait() returns false when no inspector is running (neither --inspect flags nor inspector.open()), and waitForDebugger throws ERR_INSPECTOR_NOT_ACTIVE.

Source

Thrown at ext/node/polyfills/inspector.js:278

    },
  };
}

function close() {
  op_inspector_close();
}

function url() {
  const u = op_inspector_url();
  if (u === null) {
    return undefined;
  }
  return u;
}

function waitForDebugger() {
  if (!op_inspector_wait()) {
    throw new ERR_INSPECTOR_NOT_ACTIVE();
  }
}

function broadcastToFrontend(eventName, params) {
  validateString(eventName, "eventName");
  if (params) {
    validateObject(params, "params");
  }
  op_inspector_emit_protocol_event(eventName, JSONStringify(params ?? {}));
}

function broadcastNetworkData(eventName, params) {
  if (params && params.data !== undefined) {
    const encoded = encodeNetworkData(params.data);
    if (encoded !== params.data) {
      params = ObjectAssign({ __proto__: null }, params, { data: encoded });
    }
  }

View on GitHub (pinned to 9ad36f7a2c)

Solutions

1. Launch with --inspect-brk (breaks before start and enables the inspector) and keep the waitForDebugger call.
2. Or activate programmatically first: inspector.open(); inspector.waitForDebugger().
3. Gate the call behind a debug flag/env var so normal runs skip it.

Example fix

// before - deno run app.ts (no inspector)
inspector.waitForDebugger(); // ERR_INSPECTOR_NOT_ACTIVE

// after - deno run --inspect-brk app.ts
inspector.waitForDebugger();

import inspector from 'node:inspector';
function waitForDebuggerSafe() {
  if (inspector.url() === undefined) return false; // inspector not active
  inspector.waitForDebugger();
  return true;
}

import inspector from 'node:inspector';
function canWaitForDebugger() {
  return inspector.url() !== undefined;
}

When it happens

Trigger: Calling inspector.waitForDebugger() under a plain `deno run app.ts` (no --inspect, no prior inspector.open()); calling it after inspector.close().

Common situations: A 'pause until debugger attaches' helper left enabled in CI where no inspector flag is set; ported Node debugging workflows where the launch flag was forgotten.

Related errors

• ERR_INSPECTOR_ALREADY_ACTIVATED
• Expected data to be a string, Buffer, Uint8Array, or ArrayBu
• ERR_INSPECTOR_ALREADY_CONNECTED
• ERR_INSPECTOR_NOT_WORKER
• ERR_INSPECTOR_NOT_CONNECTED

AI-assisted analysis of denoland/deno@9ad36f7a2c (2026-08-20). Data as JSON: /api/errors/826a4b1e22808123. Report an issue: GitHub.