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Cloud Debugger: Node.js Client

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This module provides Snapshot Debugger support for Node.js applications. Snapshot Debugger is an open source product that lets you debug your applications in production without stopping or pausing your application.

A Firebase Realtime Database instance is used to store your data.

Project Status: Archived

This project has been archived and is no longer supported. There will be no further bug fixes or security patches. The repository can be forked by users if they want to maintain it going forward.

A comprehensive list of changes in each version may be found in the CHANGELOG.

Read more about the client libraries for Cloud APIs, including the older Google APIs Client Libraries, in Client Libraries Explained.

Table of contents:


Before you begin

  1. Select or create a Cloud Platform project.
  2. Enable the Cloud Debugger API.
  3. Set up authentication with a service account so you can access the API from your local workstation.

Installing the client library

npm install @google-cloud/debug-agent

Debugger Agent Settings

To customize the behaviour of the automatic debugger agent, specify options when starting the agent. The following code sample shows how to pass in a subset of the available options.

  // .. auth settings ..

  // debug agent settings:
  allowExpressions: true,
  serviceContext: {
    service: 'my-service',
    version: 'version-1'
  capture: { maxFrames: 20, maxProperties: 100 }

The following options configure the connection to the Firebase database:

  • firebaseDbUrl - https://PROJECT_ID-cdbg.firebaseio.com will be used if not provided. where PROJECT_ID is your project ID.
  • firebaseKeyPath - Default google application credentials are used if not provided.

Some key configuration options are:

  • allowExpressions - Whether or not it is permitted to evaluate epressions. Functionality is limited when this is not set, but there is some risk that malicious expressions can mutate program state.
  • serviceContext - This information is utilized in the UI to identify all the running instances of your service. Set this if you do not like the default values.
  • capture - Configuration options on what is captured on a snapshot. Set this if the default snapshot captures are too limited. Note that relaxing constraints may cause performance impact.

See the agent configuration for a list of possible configuration options.

Using the Debugger

Once your application is running, use the Snapshot Debugger CLI or the VSCode extension to debug your application.

Historical note

Version 6.x and 7.x of this agent supported both the now shutdown Cloud Debugger service (by default) and the Snapshot Debugger (Firebase RTDB backend) by setting the useFirebase flag to true. Version 8.0.0 removed support for the Cloud Debugger service, making the Snapshot Debugger the default. To note the useFirebase flag is now obsolete, but still present for backward compatibility.

Limitations and Requirements

Note: There is a known issue where enabling the agent may trigger memory leaks. See #811

  • Privacy issues can be created by setting snapshot conditions that watch expressions evaluated in the context of your application. You may be able to view sensitive user data when viewing the values of variables.
  • The debug agent tries to ensure that all conditions and watchpoints you add are read-only and have no side effects. It catches, and disallows, all expressions that may have static side effects to prevent accidental state change. However, it presently does not catch expressions that have dynamic side-effects. For example, o.f looks like a property access, but dynamically, it may end up calling a getter function. We presently do NOT detect such dynamic-side effects.
  • The root directory of your application needs to contain a package.json file.


Samples are in the samples/ directory. Each sample's README.md has instructions for running its sample.

Sample Source Code Try it
App source code Open in Cloud Shell
Snippets source code Open in Cloud Shell

The Cloud Debugger Node.js Client API Reference documentation also contains samples.

Supported Node.js Versions

Our client libraries follow the Node.js release schedule. Libraries are compatible with all current active and maintenance versions of Node.js. If you are using an end-of-life version of Node.js, we recommend that you update as soon as possible to an actively supported LTS version.

Google's client libraries support legacy versions of Node.js runtimes on a best-efforts basis with the following warnings:

  • Legacy versions are not tested in continuous integration.
  • Some security patches and features cannot be backported.
  • Dependencies cannot be kept up-to-date.

Client libraries targeting some end-of-life versions of Node.js are available, and can be installed through npm dist-tags. The dist-tags follow the naming convention legacy-(version). For example, npm install @google-cloud/debug-agent@legacy-8 installs client libraries for versions compatible with Node.js 8.


This library follows Semantic Versioning.

This library is considered to be stable. The code surface will not change in backwards-incompatible ways unless absolutely necessary (e.g. because of critical security issues) or with an extensive deprecation period. Issues and requests against stable libraries are addressed with the highest priority.

More Information: Google Cloud Platform Launch Stages


Contributions welcome! See the Contributing Guide.

Please note that this README.md, the samples/README.md, and a variety of configuration files in this repository (including .nycrc and tsconfig.json) are generated from a central template. To edit one of these files, make an edit to its templates in directory.


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