# Introduction

Note

To get started quickly, use the interactive installation guide.

Certbot is part of EFF’s effort to encrypt the entire Internet. Secure communication over the Web relies on HTTPS, which requires the use of a digital certificate that lets browsers verify the identity of web servers (e.g., is that really google.com?). Web servers obtain their certificates from trusted third parties called certificate authorities (CAs). Certbot is an easy-to-use client that fetches a certificate from Let’s Encrypt—an open certificate authority launched by the EFF, Mozilla, and others—and deploys it to a web server.

Anyone who has gone through the trouble of setting up a secure website knows what a hassle getting and maintaining a certificate is. Certbot and Let’s Encrypt can automate away the pain and let you turn on and manage HTTPS with simple commands. Using Certbot and Let’s Encrypt is free, so there’s no need to arrange payment.

How you use Certbot depends on the configuration of your web server. The best way to get started is to use our interactive guide. It generates instructions based on your configuration settings. In most cases, you’ll need root or administrator access to your web server to run Certbot.

If you’re using a hosted service and don’t have direct access to your web server, you might not be able to use Certbot. Check with your hosting provider for documentation about uploading certificates or using certificates issued by Let’s Encrypt.

Certbot is a fully-featured, extensible client for the Let’s Encrypt CA (or any other CA that speaks the ACME protocol) that can automate the tasks of obtaining certificates and configuring webservers to use them. This client runs on Unix-based operating systems.

To see the changes made to Certbot between versions please refer to our changelog.

Until May 2016, Certbot was named simply `letsencrypt` or `letsencrypt-auto`, depending on install method. Instructions on the Internet, and some pieces of the software, may still refer to this older name.

## Contributing

If you’d like to contribute to this project please read Developer Guide.

## Installation

The easiest way to install Certbot is by visiting certbot.eff.org, where you can find the correct installation instructions for many web server and OS combinations. For more information, see Get Certbot.

## How to run the client

In many cases, you can just run `certbot-auto` or `certbot`, and the client will guide you through the process of obtaining and installing certs interactively.

For full command line help, you can type:

    ./certbot-auto --help all

You can also tell it exactly what you want it to do from the command line. For instance, if you want to obtain a cert for `example.com`, `www.example.com`, and `other.example.net`, using the Apache plugin to both obtain and install the certs, you could do this:

    ./certbot-auto --apache -d example.com -d www.example.com -d other.example.net

(The first time you run the command, it will make an account, and ask for an email and agreement to the Let’s Encrypt Subscriber Agreement; you can automate those with `--email` and `--agree-tos`)

If you want to use a webserver that doesn’t have full plugin support yet, you can still use “standalone” or “webroot” plugins to obtain a certificate:

    ./certbot-auto certonly --standalone --email admin@example.com -d example.com -d www.example.com -d other.example.net

## Understanding the client in more depth

To understand what the client is doing in detail, it’s important to understand the way it uses plugins. Please see the explanation of plugins in the User Guide.

### Links

Documentation: https://certbot.eff.org/docs

Software project: https://github.com/certbot/certbot

Notes for developers: https://certbot.eff.org/docs/contributing.html

Main Website: https://certbot.eff.org

Let’s Encrypt Website: https://letsencrypt.org

IRC Channel: #letsencrypt on Freenode

Community: https://community.letsencrypt.org

ACME spec: http://ietf-wg-acme.github.io/acme/

ACME working area in github: https://github.com/ietf-wg-acme/acme

### System Requirements

See https://certbot.eff.org/docs/install.html#system-requirements.