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OTP uses logback and slj4j as a logging framework. Logging is configured in the logback.xml file inside the OTP jar file. See these frameworks for more documentation on log configuration.

For developers, starting OTP using the InteractiveOtpMain is an easy way to configure debug logging.

Some loggers useful for debugging.

  • TRANSFERS_EXPORT: Dump transfers to transfers-debug.csv file.
  • DATA_IMPORT_ISSUES: Write issues to debug lag as well as to the issue report.
  • org.opentripplanner.raptor.RaptorService: Debug Raptor request and response


By default, OTP logs in plain text to the console. However, it is possible to also log in JSON format.

To enable it, set the Java property otp.logging.format to one of these values:

  • plain: regular plain text logging (default, no need to configure it)
  • json: Logstash-encoded JSON format understood by many log ingestion tools (Datadog, Loggly, Loki...)

Complete example

java -Dotp.logging.format=json -jar otp.jar --load --serve data

Further customization

If you want to customize the exact log output even further you can use your own logback configuration by starting OTP with the following parameter:

java -Dlogback.configurationFile=/path/to/logback.xml -jar otp.jar --load --serve data

For example, Entur has their own custom log format configured as follows:

<!-- Entur's custom log format  -->
<appender name="entur" class="ch.qos.logback.core.ConsoleAppender">
  <encoder class="net.logstash.logback.encoder.LoggingEventCompositeJsonEncoder">
        <!-- provides the timestamp <timestamp/> -->
        <!-- provides the version <version/> -->
        <!-- provides the fields in the configured pattern -->
           <!-- the pattern that defines what to include -->
             "serviceContext": {
               "service": "otp2"
             "message": "%message\n%ex{full}",
             "severity": "%level",
             "reportLocation": {
               "filePath": "%logger",
               "lineNumber": "%line",
               "functionName": "%method"