JSON structured logging for Rails apps (Rails 7.1 or newer, Ruby 3.3 or newer). Add the gem, and in production your app writes one JSON line per log entry to STDOUT: requests, jobs, mail, errors, security events and your own logs. The lines are easy to search, and you can turn them into metrics, alerts and dashboards in CloudWatch, Grafana, Datadog or any other log platform. Sensitive values are filtered and scrubbed before a line is written.

{"src":"rails","evt":"request","lvl":"info","ts":"2026-10-17T03:09:30.839+00:00","path":"/orders","method":"GET","source_ip":"203.0.113.7","user_agent":"Mozilla/5.0","referer":"https://app.example.com/","format":"html","controller":"OrdersController","action":"index","status":200,"duration_ms":42.1,"view":30.2,"db":8.4,"params":{"page":"2"},"host":"app.example.com","accept":"text/html","prog":"Rails","req_id":"6f1c2b7e-0d4a-4c1e-9a55-3b8e2f7d9c10"}

• On where it matters. In production LogStruct switches on for the processes it recognizes: Puma, Unicorn, Thin, Falcon, rails server, a Sidekiq server and good_job start. In test it's on for every process except the console. It's off in development, in consoles and in production Rake tasks, unless you set LOGSTRUCT_ENABLED=true. See When LogStruct runs.
• Integrations for Lograge (request lines), ActionMailer, ActiveJob, Sidekiq, GoodJob, Puma, ActiveStorage, Shrine, CarrierWave, Ahoy, ActiveModelSerializers, Dotenv, host authorization, CSRF and IP spoofing errors, and Sorbet's runtime type errors. SQL query logging is there too, off by default.
• Filtering by key name. Values under keys like password, token, api_key, authorization and cookie are replaced by a summary of the value, in request params, job arguments and anything else you log. Keys are matched by their words, so apiKey, X-Api-Key and HTTP_AUTHORIZATION are filtered too. The keys in Rails' config.filter_parameters are filtered the way Rails filters them.
• Scrubbing inside strings (inspired by Logstop): email addresses become a keyed hash ([EMAIL:5f0c1e2a9b3d4e6f]), so you can follow one person through your logs without logging the address. Card numbers that pass the Luhn check, US phone numbers, SSNs written as 123-45-6789, URL passwords, Bearer and Basic credentials and sensitive URL query params (?token=) are replaced too. IP and MAC address scrubbing are opt-in.
• Limits. Huge values are cut down (100 keys per Hash, 10 items per Array, 20 lines per backtrace, 32 KB per String by default), reducing log size and the work spent formatting large values.
• Error handling. A mode for each kind of error decides whether it's raised, logged or reported, and whether that differs between development and production. Reports go to Sentry, Bugsnag, Rollbar, Honeybadger or your own reporter.
• Sorbet types. Every built-in line is a typed struct, and you can define your own typed log lines.
• STDOUT only in production, with no log file to rotate or fill the disk.

Add this line to your application's Gemfile:

gem "logstruct"

And then run:

bundle install

That's all you need: there's nothing to generate. To configure LogStruct, add an initializer (config/initializers/logstruct.rb). The configuration docs list every setting.

To see the JSON lines in development, start your server with LOGSTRUCT_ENABLED=true rails server.

When LogStruct is on in a process:

• Rails.logger and the framework loggers (ActiveRecord, ActionController, ActionMailer, ActiveJob, ActionView, ActionCable) are replaced by LogStruct's SemanticLogger logger. A logger you set with config.logger only applies while LogStruct is off.
• Lograge is turned on and writes the request lines. Request lines include req_id, source_ip, host, user_agent, referer (without its query string), content_type, accept and the fields your lograge_custom_options proc adds.
• Every line logged during a request gets its req_id. Tags from logger.tagged(...) and config.log_tags are written in tags.
• Rails' own text lines for requests, mail and jobs are replaced by LogStruct's JSON lines. An error your app didn't handle is one error line with the request's fields and the response's status, instead of Rails' block of text.
• Mailers get a rescue_from StandardError that logs a failed delivery before re-raising it, and the log_and_ignore_error, log_and_report_error and log_and_reraise_error methods for your own rescue_from handlers (those methods exist where LogStruct is off too).
• CSRF and IP spoofing errors are logged as security lines and reported (error_handling_modes.security_errors), and Rails still responds to them as usual. Blocked hosts are logged too.
• Rails' filter_parameters list is left in place, so request.filtered_parameters, ActiveRecord::Base.filter_attributes and other Rails features keep filtering. Values Rails has already replaced are logged as [FILTERED].
• Loggers you build yourself with ActiveSupport::TaggedLogging.new(...) write LogStruct's JSON lines too.
• In production LogStruct logs to STDOUT only. In development it logs to STDOUT and Rails' log file, and in test to the log file only. With RAILS_LOG_TO_STDOUT set, both log to STDOUT only.

The full documentation is at logstruct.com/docs. Its Ruby examples are tested in this repository's test suite.

• Getting started
• Configuration
• Filtering sensitive data
• Log fields
• Custom typed logs
• Upgrading to 0.2.0 (many breaking changes)
• Troubleshooting
• Changelog

To report a vulnerability, see SECURITY.md.

This project is licensed under the MIT License. See the LICENSE file for details.