usebruno/bruno · error · Error

Port ${port} is already used by another mock server in Bruno

Error message

Port ${port} is already used by another mock server in Bruno.

What it means

Error "Port ${port} is already used by another mock server in Bruno." thrown in usebruno/bruno.

Source

Thrown at packages/bruno-electron/src/app/mock-server/mock-server.js:141

  // Editing/saving settings for a running mock: the connect probe would see our own listener.
  if (mockServerUid && isolatedServers.get(mockServerUid)?.port === normalizedPort) {
    return { available: true, reason: null };
  }

  if (!(await isPortAvailable(normalizedPort))) {
    return { available: false, reason: 'system' };
  }

  return { available: true, reason: null };
};

const assertIsolatedPortAvailable = async (requestedPort, mockServerUid) => {
  const port = Number(requestedPort) || DEFAULT_GATEWAY_PORT;
  const result = await checkPortAvailable(port, { mockServerUid });

  if (!result.available) {
    if (result.reason === 'bruno' || result.reason === 'bruno-config') {
      throw new Error(`Port ${port} is already used by another mock server in Bruno.`);
    }

    if (result.reason === 'system') {
      throw new Error(`Port ${port} is already in use on this system.`);
    }

    throw new Error(`Port ${port} is not available.`);
  }

  return port;
};

const resolveIsolatedPort = async (requestedPort, mockServerUid) => (
  assertIsolatedPortAvailable(requestedPort, mockServerUid)
);

const suggestPort = async (startPort = DEFAULT_GATEWAY_PORT, { additionalUsedPorts = [] } = {}) => {
  const used = getUsedPorts();

View on GitHub (pinned to 9bdd81c7bd)

Solutions

1. Stop the other mock server using that port, or pick a different port.
2. Check the mock server list in the workspace to find the conflict.

When it happens

Trigger: Thrown at packages/bruno-electron/src/app/mock-server/mock-server.js:141 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of usebruno/bruno@9bdd81c7bd (2026-08-13). Data as JSON: /api/errors/d78562ae5d920467. Report an issue: GitHub.