Documentation for JIRA 4.3. Documentation for other versions of JIRA is available too.

Most people scratch their head to know what parameters and Object's are in the Velocity context, the links below may come into help:

For developers, who want to know more, the DefaultVelocityManager creates a self-reference back to the VelocityContext with these lines:

    protected VelocityContext createVelocityContext(Map params)
    {
        if (params != null)
        {
            params.put("ctx", params);
        }
    ...

Therefore, doing this in the template will display the available parameters:

#foreach($p in $ctx.keySet().toArray())
  $p.toString() - $ctx.get($p).getClass().getName().toString()
#end

e.g.


  textutils - com.opensymphony.util.TextUtils
  dateformatter - com.atlassian.jira.web.util.OutlookDate
  stringUtils - org.apache.commons.lang.StringUtils
  formatter - java.text.SimpleDateFormat
  constantsManager - com.atlassian.jira.config.DefaultConstantsManager
  buildutils - com.atlassian.jira.util.BuildUtils
  i - java.lang.Integer
  context - com.atlassian.jira.mail.TemplateContext
  jiraUserUtils - com.atlassian.jira.util.JiraUserUtils
  baseurl - java.lang.String
  security - $ctx.get($p).getClass().getName().toString()
  numdashes - java.lang.Integer
  ctx - java.util.HashMap
  jirakeyutils - com.atlassian.jira.util.JiraKeyUtils
  i18n - com.atlassian.jira.web.bean.I18nBean
  recipient - com.opensymphony.user.User
  velocityCount - java.lang.Integer
  attachments - java.util.ArrayList
  remoteUser - com.opensymphony.user.User
  userutils - com.atlassian.core.user.UserUtils
  applicationProperties - com.atlassian.jira.config.properties.ApplicationPropertiesImpl
  padSize - java.lang.Integer
  customFieldManager - com.atlassian.jira.issue.managers.DefaultCustomFieldManager
  issue - com.atlassian.jira.mail.TemplateIssue
  jirautils - com.atlassian.jira.util.JiraUtils
  params - java.util.HashMap
  projectManager - com.atlassian.jira.project.CachingProjectManager
  velocityhelper - com.atlassian.jira.util.JiraVelocityHelper
  timeSpentFieldId - java.lang.String