HotCRP conference review software
Pull request Compare This branch is 10 commits ahead, 2731 commits behind kohler:master.
Fetching latest commit…
Cannot retrieve the latest commit at this time.
Failed to load latest commit information.

HotCRP Conference Review Software Build Status

HotCRP is the best available software for managing the conference review process, including paper submission, review and comment management, rebuttals, and the PC meeting. Its main strengths are flexibility and ease of use in the review process, especially through smart paper search and an extensive tagging facility. It is widely used in computer science conferences and for internal review processes at several large companies.

Multitrack conferences with per-track deadlines should use other software.

HotCRP is the open-source version of the software running on If you want to run HotCRP without setting up your own server, use


HotCRP runs on Unix, including Mac OS X. It requires the following software:

Apache is preloaded on most Linux distributions. You may need to install additional packages for PHP and MySQL, such as:

  • Fedora Linux: php-mysql, php-gd, zip, (poppler-utils)
  • Debian Linux: php5-common, php5-gd, php5-mysql, libapache2-mod-php5 (or libapache-mod-php5 for Apache 1.x), zip, (poppler-utils)
  • Ubuntu Linux: php5-common, php5-gd, php5-mysql, libapache2-mod-php5 (or libapache-mod-php5 for Apache 1.x), zip, (poppler-utils), and a package for SMTP support, such as sendmail or postfix

You may need to restart the Apache web server after installing these packages (sudo apachectl graceful or sudo apache2ctl graceful). If using nginx, you will need the php-fpm package.


  1. Run lib/ to create the database. Use lib/ OPTIONS to pass options to MySQL, such as --user and --password. Many MySQL installations require privilege to create tables, so you may need sudo lib/ OPTIONS. Run lib/ --help for more information. You will need to decide on a name for your database (no spaces allowed).

    The username and password information for the conference database is stored in conf/options.php, which HotCRP marks as world-unreadable. You must ensure that your PHP can read this file.

  2. Edit conf/options.php, which is annotated to guide you. (lib/ creates this file based on src/distoptions.php.)

  3. Configure your web server to access HotCRP. The right way to do this depends on which server you’re running.

    Nginx: Configure Nginx to access php-fpm for anything under the HotCRP URL path. All accesses should be redirected to index.php. This example, which would go in a server block, makes /testconf point at a HotCRP installation in /home/kohler/hotcrp (assuming that the running php-fpm is listening on port 9000):

     location /testconf/ {
         fastcgi_split_path_info ^(/testconf)(/.*)$;
         fastcgi_param PATH_INFO $fastcgi_path_info;
         fastcgi_param SCRIPT_FILENAME /home/kohler/hotcrp/index.php;
         include fastcgi_params;

    You may also set up separate location blocks so that Nginx serves files under images/, scripts/, and stylesheets/ directly.

    Apache: Generally you must add a <Directory> to httpd.conf (or one of its inclusions) for the HotCRP directory, and an Alias redirecting your preferred URL path to that directory. This example makes /testconf point at a HotCRP installation in /home/kohler/hotcrp:

     # Apache 2.2 and earlier:
     <Directory "/home/kohler/hotcrp">
         Options Indexes Includes FollowSymLinks
         AllowOverride all
         Order allow,deny
         Allow from all
     Alias /testconf /home/kohler/hotcrp
     # Apache 2.4 and later:
     <Directory "/home/kohler/hotcrp">
         Options Indexes Includes FollowSymLinks
         AllowOverride all
         Require all granted
     Alias /testconf /home/kohler/hotcrp

    Note that the first argument to Alias should NOT end in a slash. The AllowOverride all directive is required.

    Everything under HotCRP’s URL path (here, /testconf) should be served by HotCRP. This normally happens automatically. However, if the URL path is /, you may need to turn off your server’s default handlers for subdirectories such as /doc.

  4. Update PHP settings.

    The first three settings, upload_max_filesize, post_max_size, and max_input_vars, may be changed system-wide or in HotCRP’s .htaccess and .user.ini files.

  • upload_max_filesize: Set to the largest file upload HotCRP should accept. 15M is a good default.

  • post_max_size: Set to the largest total upload HotCRP should accept. Must be at least as big as upload_max_filesize. 20M is a good default.

  • max_input_vars: Set to the largest number of distinct input variables HotCRP should accept. 4096 is a good default.

    The last setting, session.gc_maxlifetime, must be changed globally. This provides an upper bound on HotCRP session lifetimes (the amount of idle time before a user is logged out automatically). On Unix machines, systemwide PHP settings are often stored in /etc/php.ini. The suggested value for this setting is 86400, e.g., 24 hours:

    session.gc_maxlifetime = 86400

    If you want sessions to expire sooner, we recommend you set session.gc_maxlifetime to 86400 anyway, then edit conf/options.php to set $Opt["sessionLifetime"] to the correct session timeout.

  1. Edit MySQL’s my.cnf (typical location: /etc/mysql/my.cnf) to ensure that MySQL can handle paper-sized objects. It should contain something like this:


    max_allowed_packet must be at least as large as the largest paper you are willing to accept. It defaults to 1M on some systems, which is not nearly large enough. HotCRP will warn you if it is too small. Some MySQL setups, such as on Mac OS X, may not have a my.cnf by default; just create one. If you edit my.cnf, also restart the mysqld server. On Linux try something like sudo /etc/init.d/mysql restart.

  2. Sign in to the site to create an account. The first account created automatically receives system administrator privilege.

You can set up everything else through the web site itself.

  • Configuration notes

    • Uploaded papers and reviews are limited in size by several PHP configuration variables, set by default to 15 megabytes in the HotCRP directory’s .htaccess (or .user.ini if you are using php-fpm).

    • HotCRP PHP scripts can take a lot of memory, particularly if they're doing things like generating MIME-encoded mail messages. By default HotCRP sets the PHP memory limit to 128MB.

    • HotCRP benefits from Apache’s mod_expires and mod_rewrite modules; consider enabling them.

    • Most HotCRP settings are assigned in the conference database’s Settings table. The Settings table can also override values in conf/options.php: a Settings record with name "opt.XXX" takes precedence over option $Opt["XXX"].

Database access

Run lib/ at the shell prompt to back up the database. This will write the database’s current structure and comments to the standard output. As typically configured, HotCRP stores all paper submissions in the database, so the backup file may be quite large.

Run lib/ BACKUPFILE at the shell prompt to restore the database from a backup stored in BACKUPFILE.

Run lib/ at the shell prompt to get a MySQL command prompt for the conference database.


HotCRP code can be updated at any time without bringing down the site. If you obtained the code from git, use git pull. if you obtained the code from a tarball, copy the new version over your old code, preserving conf/options.php. For instance, using GNU tar:

% tar --strip=1 -xf ~/hotcrp-NEWVERSION.tar.gz

Multiconference support

HotCRP can run multiple conferences from a single installation. The last directory component of the URL will define the conference ID. For instance:
                                       conference ID

The conference ID can only contain characters in [-_.A-Za-z0-9], and it must not start with a period. HotCRP will check for funny conference IDs and replace them with __invalid__.

To turn on multiconference support:

  1. Set your Web server to use the HotCRP install directory for all relevant URLs. For Apache, this may require an Alias directive per conference.

  2. Set $Opt["multiconference"] to true in conf/options.php. This will set the conference ID to the last directory component as described above. Alternately, set $Opt["multiconferenceAnalyzer"] to a regular expression, a space, and a replacement pattern. HotCRP matches the full input URL to the regex, then uses the replacement pattern as the conference ID. For example, this setting will use "conf_CONFNAME" as the conference ID for a URL like "":

     $Opt["multiconferenceAnalyzer"] = '\w+://([^./]+)\.crap\.com\.?/ conf_$1';
  3. Set HotCRP options to locate the options relevant for each conference. The best mechanism is to use $Opt["include"] to include a conference-specific options file. For example (note the single quotes):

     $Opt["include"] = 'conf/options-${confid}.php';

    The ${confid} substring is replaced with the conference ID. HotCRP will refuse to proceed if the conference-specific options file doesn’t exist. To ignore nonexistent options files, use wildcards:

     $Opt["include"] = 'conf/[o]ptions-${confid}.php';

    ${confid} replacement is also performed on these $Opt settings: dbName, dbUser, dbPassword, sessionName, downloadPrefix, conferenceSite, paperSite, defaultPaperSite, contactName, contactEmail, emailFrom, emailSender, emailCc, emailReplyTo, and docstore.

  4. Each conference needs its own database. Create one using the lib/ script (the -c CONFIGFILE option will be useful).


HotCRP is available under the Click license, a BSD-like license. See the LICENSE file for full license terms.


Eddie Kohler, Harvard/UCLA