Log Fields

Each line LogStruct writes is one JSON object. This page lists its keys: the ones every line has, the ones LogStruct adds from the logger's context, and the short names of each log type's fields. It ends with an example line for each built-in log type and the formats of the values.

Keys on Every Line

Key	Value
src	Where the line came from: a `LogStruct::Source` value such as `rails`, `app`, `job` or `mailer`, or the `src` of a Hash you log. Lines without one get `app`.
evt	What happened: a `LogStruct::Event` value such as `request`, `log` or `error`, or the `evt` of a Hash you log. Lines without one get `log`.
lvl	The level the line was logged at (see Levels).
ts	When the line was logged (see Timestamps).
msg	The message, on lines that have one: a string you log, the message field of the log types that have one (see Short Names), or the `msg` of a Hash you log.
prog	The name of the logger that wrote the line: `Rails` for `Rails.logger` and the framework loggers LogStruct replaces, `Sidekiq-Server` or `Sidekiq-Client` for Sidekiq's own lines and `GoodJob` for GoodJob's. Lines written without a logger name have no `prog`.

LogStruct's own log types write src, evt, lvl and ts first, then their fields. A Hash you log keeps its own keys first.

Keys from the Logger's Context

LogStruct adds these keys after the line's own fields. It filters and scrubs them like the rest of the line.

Key	Value
req_id	The request's ID (Rails' `request.request_id`), on every line logged while Rails handles a request. Blocked host lines don't have it: Rails checks the host before it sets the request ID. A line with its own `req_id` keeps it.
tags	The logger's tags, as an array: `logger.tagged("billing")` and `config.log_tags`. The `config/environments/production.rb` that Rails generates sets `config.log_tags = [:request_id]`, so the lines logged during a request in production have the request ID in `tags` too. A line with its own `tags` keeps them.
ctx	Named tags (`logger.tagged(account_id: 42)`) and, while a Sidekiq job runs, the job's `jid` and `class`. When a line has its own `ctx` Hash, its keys win and the other keys are added to it.

Rails.logger.tagged("billing") do
  Rails.logger.tagged(account_id: 42) do
    Rails.logger.info("Charged card")
  end
end

{
  "src": "app",
  "evt": "log",
  "lvl": "info",
  "ts": "2026-10-17T09:30:15.123+00:00",
  "msg": "Charged card",
  "prog": "Rails",
  "tags": [
    "billing"
  ],
  "req_id": "6f1c9a2e-7b4d-4e8a-9c61-2d5b8f0e4a17",
  "ctx": {
    "account_id": 42
  }
}

Logged Hashes

A Hash you log is written with its keys at the top level of the line. It can set its own src and evt. The timestamp and level come from the logger: a ts or lvl key in the Hash is dropped and handled as a LogStruct error (error_handling_modes.logstruct_errors: raised in local_environments, logged elsewhere).

Rails.logger.info(msg: "Invoice sent", invoice_id: 812, email: "Linda.Martinez@example.com")

{
  "msg": "Invoice sent",
  "invoice_id": 812,
  "email": {
    "_filtered": {
      "_class": "String",
      "_hash": "a058d5090035d2e1"
    }
  },
  "src": "app",
  "evt": "log",
  "ts": "2026-10-17T09:30:15.123+00:00",
  "lvl": "info",
  "prog": "Rails",
  "req_id": "6f1c9a2e-7b4d-4e8a-9c61-2d5b8f0e4a17"
}

additional_data

LogStruct's log types take an additional_data Hash for fields the type doesn't have. Its keys are written at the top level of the line, after the type's own fields, not under an additional_data key.

Rails.logger.info(
  LogStruct::Log::Plain.new(
    message: "Imported invoices",
    additional_data: {account_id: 42, rows: 120}
  )
)

{
  "src": "app",
  "evt": "log",
  "lvl": "info",
  "ts": "2026-10-17T09:30:15.123+00:00",
  "msg": "Imported invoices",
  "account_id": 42,
  "rows": 120,
  "prog": "Rails"
}

A key with the same name as one of the type's fields replaces that field: an additional_data of {msg: "..."} replaces the message.
src, evt, lvl and ts are reserved. LogStruct drops them and handles the ArgumentError as a LogStruct error (raised in local_environments, logged elsewhere).

Short Names

LogStruct's log types name their fields with LogStruct::LogField, which maps each name to a short JSON key: MailerClass is written as mailer and Database as db. The table lists every field. Log::ActiveJob::* stands for every ActiveJob log type, and some fields aren't written by any built-in log type. At the top of a line, Rails' partial filter_parameters matches don't apply to these keys: Rails 8's default :_key would otherwise filter cron_key.

Key	LogField	Written by
accept	Accept	Log::Request
action	Action	Log::Request
active_count	ActiveConnections	Log::SQL
adapter	Adapter	Log::ActiveModelSerializers, Log::SQL
addr	Address	No built-in log type
ahoy_event	AhoyEvent	Log::Ahoy
allow_ip_hosts	AllowIpHosts	No built-in log type
allowed_hosts	AllowedHosts	No built-in log type
arguments	Arguments	Log::ActiveJob::, Log::GoodJob::
attachments	AttachmentCount	Log::ActionMailer::*
attempt	Attempt	Log::ActiveJob::Start
backtrace	Backtrace	Log::ActionMailer::Error, Log::ActiveJob::Error, Log::Error, Log::GoodJob::Error, Log::Puma::Error, Log::Sidekiq::Error
bind_params	BindParams	Log::SQL
blocked_host	BlockedHost	Log::Security::BlockedHost
blocked_hosts	BlockedHosts	Log::Security::BlockedHost
cause_class	CauseClass	Log::Error
cause_message	CauseMessage	Log::Error
checksum	Checksum	Log::ActiveStorage::Upload
client_ip	ClientIp	Log::Security::IPSpoof
content_type	ContentType	Log::Request
controller	Controller	Log::Request
cron_key	CronKey	No built-in log type
ctx	Context	Log::Sidekiq::Log
data	Data	No built-in log type
db	Database	Log::Request
db_name	DatabaseName	Log::SQL
download_opts	DownloadOptions	Log::Shrine::Download
duration_ms	DurationMs	Log::ActiveJob::Finish, Log::ActiveModelSerializers, Log::ActiveStorage::Download, Log::ActiveStorage::Upload, Log::CarrierWave::Upload, Log::GoodJob::Error, Log::Request, Log::SQL, Log::Shrine::Metadata, Log::Shrine::Upload
enqueue_caller	EnqueueCaller	No built-in log type
environment	Environment	Log::Puma::Start
error_class	ErrorClass	Log::ActionMailer::Error, Log::ActiveJob::Discard, Log::ActiveJob::Error, Log::ActiveJob::Retry, Log::ActiveJob::RetryStopped, Log::Error, Log::GoodJob::Error, Log::Puma::Error, Log::Sidekiq::Error
error_context	ErrorContext	Log::Puma::Error, Log::Sidekiq::Error
error_message	ErrorMessage	Log::Error, Log::GoodJob::Error
evt	Event	Every log type
exception_executions	ExceptionExecutions	Log::GoodJob::Error
execution_time	ExecutionTime	No built-in log type
executions	Executions	Log::ActiveJob::, Log::GoodJob::
exist	Exist	Log::ActiveStorage::Exist
ext	Extension	Log::CarrierWave::*
file	File	Log::Dotenv::Load
file_id	FileId	Log::ActiveStorage::, Log::CarrierWave::
filename	Filename	Log::CarrierWave::Download, Log::CarrierWave::Upload
finished_at	FinishedAt	Log::ActiveJob::Finish
format	Format	Log::Request
from	From	Log::ActionMailer::*
host	Host	Log::Request
job_class	JobClass	Log::ActiveJob::, Log::GoodJob::
job_id	JobId	Log::ActiveJob::, Log::GoodJob::
listening_addresses	ListeningAddresses	Log::Puma::Start
location	Location	Log::Shrine::Delete, Log::Shrine::Download, Log::Shrine::Exist, Log::Shrine::Upload
lvl	Level	Every log type
mailer	MailerClass	Log::ActionMailer::*
mailer_action	MailerAction	Log::ActionMailer::*
max_threads	MaxThreads	Log::Puma::Start
metadata	Metadata	Log::CarrierWave::Upload
method	HttpMethod	Log::Error, Log::Puma::Error, Log::Request, Log::Security::*
mime_type	MimeType	Log::ActiveStorage::Metadata, Log::CarrierWave::Download, Log::CarrierWave::Upload, Log::Shrine::Upload
min_threads	MinThreads	Log::Puma::Start
mode	Mode	Log::Puma::Start
model	Model	Log::CarrierWave::*
mount_point	MountPoint	Log::CarrierWave::*
msg	Message	Log::ActionMailer::Error, Log::ActiveJob::Discard, Log::ActiveJob::Error, Log::ActiveJob::Retry, Log::ActiveJob::RetryStopped, Log::ActiveModelSerializers, Log::Ahoy, Log::Error, Log::GoodJob::Log, Log::Plain, Log::Puma::Error, Log::SQL, Log::Security::, Log::Sidekiq::
msg_id	MessageId	Log::ActionMailer::*
name	Name	Log::SQL
op	Operation	No built-in log type
op_type	OperationType	Log::SQL
opts	Options	Log::Shrine::Upload
params	Params	Log::Request
path	Path	Log::Error, Log::Puma::Error, Log::Request, Log::Security::*
pid	ProcessId	Log::GoodJob::*, Log::Puma::Shutdown, Log::Puma::Start, Log::Sidekiq::Log
pool_size	ConnectionPoolSize	Log::SQL
prefix	Prefix	Log::ActiveStorage::Delete
priority	Priority	Log::GoodJob::Log
properties	Properties	Log::Ahoy
provider_job_id	ProviderJobId	Log::ActiveJob::*
puma_codename	PumaCodename	Log::Puma::Start
puma_version	PumaVersion	Log::Puma::Start
queue_name	QueueName	Log::ActiveJob::, Log::GoodJob::, Log::Sidekiq::Error
range	Range	Log::ActiveStorage::Download
referer	Referer	Log::Error, Log::Request, Log::Security::*
req_id	RequestId	Added from the request (see above)
resource_class	ResourceClass	Log::ActiveModelSerializers
result	Result	No built-in log type
retries	Retries	No built-in log type
retry_count	RetryCount	Log::Sidekiq::Error
row_count	RowCount	Log::SQL
ruby_version	RubyVersion	Log::Puma::Start
run_time	RunTime	No built-in log type
scheduled_at	ScheduledAt	Log::ActiveJob::Schedule, Log::GoodJob::Log
serializer	Serializer	Log::ActiveModelSerializers
size	Size	Log::CarrierWave::Download, Log::CarrierWave::Upload, Log::Shrine::Upload
snapshot	Snapshot	Log::Dotenv::Save
source_ip	SourceIp	Log::Error, Log::Request, Log::Security::*
sql	Sql	Log::SQL
src	Source	Every log type
started_at	StartedAt	Log::ActiveJob::Start
status	Status	Log::Error, Log::Request
storage	Storage	Log::ActiveStorage::, Log::CarrierWave::, Log::Shrine::*
store_path	StorePath	Log::CarrierWave::*
subject	Subject	Log::ActionMailer::*
table_names	TableNames	Log::SQL
tid	ThreadId	Log::GoodJob::*, Log::Sidekiq::Log
to	To	Log::ActionMailer::*
ts	Timestamp	Every log type
upload_opts	UploadOptions	Log::Shrine::Upload
uploader	Uploader	Log::CarrierWave::*, Log::Shrine::Upload
url	Url	No built-in log type
user_agent	UserAgent	Log::Error, Log::Request, Log::Security::*
vars	Vars	Log::Dotenv::Restore, Log::Dotenv::Update
version	Version	Log::CarrierWave::*
view	View	Log::Request
wait_ms	WaitMs	Log::ActiveJob::Retry
wait_time	WaitTime	No built-in log type
x_forwarded_for	XForwardedFor	Log::Security::BlockedHost, Log::Security::IPSpoof

Example Lines

One line for each built-in log type, as LogStruct's formatter writes it from the values its integration sets. The values are made up. Each line is shown over several lines here; LogStruct writes it on one. The fields of each type are listed in Built-In Log Classes.

`Log::ActionMailer`

Log::ActionMailer::Delivered src: mailer, evt: delivered

{
  "src": "mailer",
  "evt": "delivered",
  "lvl": "info",
  "ts": "2026-10-17T09:30:15.123+00:00",
  "to": [
    "[EMAIL:a058d5090035d2e1]"
  ],
  "from": "[EMAIL:a6778e226026bac8]",
  "subject": "Your October invoice",
  "msg_id": "[EMAIL:ff61c70b949f216c]",
  "mailer": "InvoiceMailer",
  "mailer_action": "monthly",
  "attachments": 1,
  "account_id": 42,
  "user_id": 1873,
  "prog": "Rails",
  "req_id": "6f1c9a2e-7b4d-4e8a-9c61-2d5b8f0e4a17"
}

Log::ActionMailer::Delivery src: mailer, evt: delivery

{
  "src": "mailer",
  "evt": "delivery",
  "lvl": "info",
  "ts": "2026-10-17T09:30:15.123+00:00",
  "to": [
    "[EMAIL:a058d5090035d2e1]"
  ],
  "from": "[EMAIL:a6778e226026bac8]",
  "subject": "Your October invoice",
  "mailer": "InvoiceMailer",
  "mailer_action": "monthly",
  "attachments": 1,
  "account_id": 42,
  "user_id": 1873,
  "prog": "Rails",
  "req_id": "6f1c9a2e-7b4d-4e8a-9c61-2d5b8f0e4a17"
}

Log::ActionMailer::Error src: mailer, evt: error

{
  "src": "mailer",
  "evt": "error",
  "lvl": "error",
  "ts": "2026-10-17T09:30:15.123+00:00",
  "to": [
    "[EMAIL:a058d5090035d2e1]"
  ],
  "from": "[EMAIL:a6778e226026bac8]",
  "subject": "Your October invoice",
  "mailer": "InvoiceMailer",
  "mailer_action": "monthly",
  "attachments": 1,
  "error_class": "Net::SMTPAuthenticationError",
  "msg": "Net::SMTPAuthenticationError: Email delivery failed. Recipients: [EMAIL:a6778e226026bac8]. Error message: 535 5.7.8 Authentication failed",
  "backtrace": [
    "app/mailers/invoice_mailer.rb:12:in 'InvoiceMailer#monthly'"
  ],
  "account_id": 42,
  "user_id": 1873,
  "prog": "Rails",
  "ctx": {
    "jid": "b4a9c63e5f1d2a7e9c0f3b18",
    "class": "ActionMailer::MailDeliveryJob"
  }
}

`Log::ActiveJob`

Log::ActiveJob::Discard src: job, evt: discard

{
  "src": "job",
  "evt": "discard",
  "lvl": "error",
  "ts": "2026-10-17T09:30:15.123+00:00",
  "job_id": "c2b8e0f4-1d3a-4b6c-9e7f-5a1d2c3b4e5f",
  "job_class": "InvoiceExportJob",
  "queue_name": "default",
  "arguments": [
    "gid://my-app/Customer/1873",
    {
      "month": "2026-09",
      "email": {
        "_filtered": {
          "_class": "String",
          "_hash": "a058d5090035d2e1"
        }
      }
    }
  ],
  "executions": 1,
  "provider_job_id": "b4a9c63e5f1d2a7e9c0f3b18",
  "error_class": "ActiveJob::DeserializationError",
  "msg": "Error while trying to deserialize arguments: Couldn't find Customer",
  "prog": "Rails",
  "ctx": {
    "jid": "b4a9c63e5f1d2a7e9c0f3b18",
    "class": "InvoiceExportJob"
  }
}

Log::ActiveJob::Enqueue src: job, evt: enqueue

{
  "src": "job",
  "evt": "enqueue",
  "lvl": "info",
  "ts": "2026-10-17T09:30:15.123+00:00",
  "job_id": "c2b8e0f4-1d3a-4b6c-9e7f-5a1d2c3b4e5f",
  "job_class": "InvoiceExportJob",
  "queue_name": "default",
  "arguments": [
    "gid://my-app/Customer/1873",
    {
      "month": "2026-09",
      "email": {
        "_filtered": {
          "_class": "String",
          "_hash": "a058d5090035d2e1"
        }
      }
    }
  ],
  "executions": 0,
  "provider_job_id": "b4a9c63e5f1d2a7e9c0f3b18",
  "prog": "Rails",
  "req_id": "6f1c9a2e-7b4d-4e8a-9c61-2d5b8f0e4a17"
}

Log::ActiveJob::Error src: job, evt: error

{
  "src": "job",
  "evt": "error",
  "lvl": "error",
  "ts": "2026-10-17T09:30:15.123+00:00",
  "job_id": "c2b8e0f4-1d3a-4b6c-9e7f-5a1d2c3b4e5f",
  "job_class": "InvoiceExportJob",
  "queue_name": "default",
  "arguments": [
    "gid://my-app/Customer/1873",
    {
      "month": "2026-09",
      "email": {
        "_filtered": {
          "_class": "String",
          "_hash": "a058d5090035d2e1"
        }
      }
    }
  ],
  "executions": 1,
  "provider_job_id": "b4a9c63e5f1d2a7e9c0f3b18",
  "error_class": "Net::ReadTimeout",
  "msg": "Net::ReadTimeout with #<TCPSocket:(closed)>",
  "backtrace": [
    "app/services/invoice_export.rb:42:in 'InvoiceExport#upload'",
    "app/services/invoice_export.rb:18:in 'InvoiceExport#call'",
    "app/jobs/invoice_export_job.rb:9:in 'InvoiceExportJob#perform'"
  ],
  "prog": "Rails",
  "ctx": {
    "jid": "b4a9c63e5f1d2a7e9c0f3b18",
    "class": "InvoiceExportJob"
  }
}

Log::ActiveJob::Finish src: job, evt: finish

{
  "src": "job",
  "evt": "finish",
  "lvl": "info",
  "ts": "2026-10-17T09:30:15.935+00:00",
  "job_id": "c2b8e0f4-1d3a-4b6c-9e7f-5a1d2c3b4e5f",
  "job_class": "InvoiceExportJob",
  "queue_name": "default",
  "arguments": [
    "gid://my-app/Customer/1873",
    {
      "month": "2026-09",
      "email": {
        "_filtered": {
          "_class": "String",
          "_hash": "a058d5090035d2e1"
        }
      }
    }
  ],
  "executions": 1,
  "provider_job_id": "b4a9c63e5f1d2a7e9c0f3b18",
  "duration_ms": 812.43,
  "finished_at": "2026-10-17T09:30:15.935+00:00",
  "prog": "Rails",
  "ctx": {
    "jid": "b4a9c63e5f1d2a7e9c0f3b18",
    "class": "InvoiceExportJob"
  }
}

Log::ActiveJob::Retry src: job, evt: retry

{
  "src": "job",
  "evt": "retry",
  "lvl": "info",
  "ts": "2026-10-17T09:30:15.123+00:00",
  "job_id": "c2b8e0f4-1d3a-4b6c-9e7f-5a1d2c3b4e5f",
  "job_class": "InvoiceExportJob",
  "queue_name": "default",
  "arguments": [
    "gid://my-app/Customer/1873",
    {
      "month": "2026-09",
      "email": {
        "_filtered": {
          "_class": "String",
          "_hash": "a058d5090035d2e1"
        }
      }
    }
  ],
  "executions": 1,
  "provider_job_id": "b4a9c63e5f1d2a7e9c0f3b18",
  "error_class": "Net::ReadTimeout",
  "msg": "Net::ReadTimeout with #<TCPSocket:(closed)>",
  "wait_ms": 3000,
  "prog": "Rails",
  "ctx": {
    "jid": "b4a9c63e5f1d2a7e9c0f3b18",
    "class": "InvoiceExportJob"
  }
}

Log::ActiveJob::RetryStopped src: job, evt: retry_stopped

{
  "src": "job",
  "evt": "retry_stopped",
  "lvl": "error",
  "ts": "2026-10-17T09:30:15.123+00:00",
  "job_id": "c2b8e0f4-1d3a-4b6c-9e7f-5a1d2c3b4e5f",
  "job_class": "InvoiceExportJob",
  "queue_name": "default",
  "arguments": [
    "gid://my-app/Customer/1873",
    {
      "month": "2026-09",
      "email": {
        "_filtered": {
          "_class": "String",
          "_hash": "a058d5090035d2e1"
        }
      }
    }
  ],
  "executions": 5,
  "provider_job_id": "b4a9c63e5f1d2a7e9c0f3b18",
  "error_class": "Net::ReadTimeout",
  "msg": "Net::ReadTimeout with #<TCPSocket:(closed)>",
  "prog": "Rails",
  "ctx": {
    "jid": "b4a9c63e5f1d2a7e9c0f3b18",
    "class": "InvoiceExportJob"
  }
}

Log::ActiveJob::Schedule src: job, evt: schedule

{
  "src": "job",
  "evt": "schedule",
  "lvl": "info",
  "ts": "2026-10-17T09:30:15.123+00:00",
  "job_id": "c2b8e0f4-1d3a-4b6c-9e7f-5a1d2c3b4e5f",
  "job_class": "InvoiceExportJob",
  "queue_name": "default",
  "arguments": [
    "gid://my-app/Customer/1873",
    {
      "month": "2026-09",
      "email": {
        "_filtered": {
          "_class": "String",
          "_hash": "a058d5090035d2e1"
        }
      }
    }
  ],
  "executions": 0,
  "provider_job_id": "b4a9c63e5f1d2a7e9c0f3b18",
  "scheduled_at": "2026-10-17T10:30:15.123+00:00",
  "prog": "Rails",
  "req_id": "6f1c9a2e-7b4d-4e8a-9c61-2d5b8f0e4a17"
}

Log::ActiveJob::Start src: job, evt: start

{
  "src": "job",
  "evt": "start",
  "lvl": "info",
  "ts": "2026-10-17T09:30:15.123+00:00",
  "job_id": "c2b8e0f4-1d3a-4b6c-9e7f-5a1d2c3b4e5f",
  "job_class": "InvoiceExportJob",
  "queue_name": "default",
  "arguments": [
    "gid://my-app/Customer/1873",
    {
      "month": "2026-09",
      "email": {
        "_filtered": {
          "_class": "String",
          "_hash": "a058d5090035d2e1"
        }
      }
    }
  ],
  "executions": 1,
  "provider_job_id": "b4a9c63e5f1d2a7e9c0f3b18",
  "started_at": "2026-10-17T09:30:15.123+00:00",
  "attempt": 1,
  "prog": "Rails",
  "ctx": {
    "jid": "b4a9c63e5f1d2a7e9c0f3b18",
    "class": "InvoiceExportJob"
  }
}

`Log::ActiveModelSerializers`

Log::ActiveModelSerializers src: rails, evt: generate

{
  "src": "rails",
  "evt": "generate",
  "lvl": "info",
  "ts": "2026-10-17T09:30:15.123+00:00",
  "msg": "ams.render",
  "serializer": "InvoiceSerializer",
  "adapter": "ActiveModelSerializers::Adapter::Attributes",
  "resource_class": "Invoice",
  "duration_ms": 1.241,
  "prog": "Rails",
  "req_id": "6f1c9a2e-7b4d-4e8a-9c61-2d5b8f0e4a17"
}

`Log::ActiveStorage`

Log::ActiveStorage::Delete src: storage, evt: delete

{
  "src": "storage",
  "evt": "delete",
  "lvl": "info",
  "ts": "2026-10-17T09:30:15.123+00:00",
  "storage": "S3",
  "file_id": "m3k9x2q7w1c8v4b6n0z5h2j7",
  "prog": "Rails"
}

Log::ActiveStorage::Download src: storage, evt: download

{
  "src": "storage",
  "evt": "download",
  "lvl": "info",
  "ts": "2026-10-17T09:30:15.123+00:00",
  "storage": "S3",
  "file_id": "m3k9x2q7w1c8v4b6n0z5h2j7",
  "duration_ms": 96.12,
  "prog": "Rails",
  "req_id": "6f1c9a2e-7b4d-4e8a-9c61-2d5b8f0e4a17"
}

Log::ActiveStorage::Exist src: storage, evt: exist

{
  "src": "storage",
  "evt": "exist",
  "lvl": "debug",
  "ts": "2026-10-17T09:30:15.123+00:00",
  "storage": "S3",
  "file_id": "m3k9x2q7w1c8v4b6n0z5h2j7",
  "exist": true,
  "prog": "Rails",
  "req_id": "6f1c9a2e-7b4d-4e8a-9c61-2d5b8f0e4a17"
}

Log::ActiveStorage::Metadata src: storage, evt: metadata

{
  "src": "storage",
  "evt": "metadata",
  "lvl": "info",
  "ts": "2026-10-17T09:30:15.123+00:00",
  "storage": "S3",
  "file_id": "m3k9x2q7w1c8v4b6n0z5h2j7",
  "mime_type": "application/pdf",
  "prog": "Rails"
}

Log::ActiveStorage::Upload src: storage, evt: upload

{
  "src": "storage",
  "evt": "upload",
  "lvl": "info",
  "ts": "2026-10-17T09:30:15.123+00:00",
  "storage": "S3",
  "file_id": "m3k9x2q7w1c8v4b6n0z5h2j7",
  "duration_ms": 184.3,
  "checksum": "3Ys4l0pZ8wQ1mH7cE2uXrA==",
  "prog": "Rails",
  "req_id": "6f1c9a2e-7b4d-4e8a-9c61-2d5b8f0e4a17"
}

Log::ActiveStorage::Url src: storage, evt: url

{
  "src": "storage",
  "evt": "url",
  "lvl": "debug",
  "ts": "2026-10-17T09:30:15.123+00:00",
  "storage": "S3",
  "file_id": "m3k9x2q7w1c8v4b6n0z5h2j7",
  "prog": "Rails",
  "req_id": "6f1c9a2e-7b4d-4e8a-9c61-2d5b8f0e4a17"
}

`Log::Ahoy`

Log::Ahoy src: app, evt: log

{
  "src": "app",
  "evt": "log",
  "lvl": "info",
  "ts": "2026-10-17T09:30:15.123+00:00",
  "msg": "ahoy.track",
  "ahoy_event": "Viewed invoice",
  "properties": {
    "invoice_id": 812
  },
  "prog": "Rails",
  "req_id": "6f1c9a2e-7b4d-4e8a-9c61-2d5b8f0e4a17"
}

`Log::CarrierWave`

Log::CarrierWave::Delete src: carrierwave, evt: delete

{
  "src": "carrierwave",
  "evt": "delete",
  "lvl": "info",
  "ts": "2026-10-17T09:30:15.123+00:00",
  "storage": "file",
  "file_id": "avatar.png",
  "uploader": "AvatarUploader",
  "model": "User",
  "mount_point": "avatar",
  "version": "",
  "store_path": "uploads/user/avatar/1873/avatar.png",
  "ext": "png",
  "prog": "Rails",
  "req_id": "6f1c9a2e-7b4d-4e8a-9c61-2d5b8f0e4a17"
}

Log::CarrierWave::Download src: carrierwave, evt: download

{
  "src": "carrierwave",
  "evt": "download",
  "lvl": "info",
  "ts": "2026-10-17T09:30:15.123+00:00",
  "storage": "file",
  "file_id": "avatar.png",
  "uploader": "AvatarUploader",
  "model": "User",
  "mount_point": "avatar",
  "version": "",
  "store_path": "uploads/user/avatar/1873/avatar.png",
  "ext": "png",
  "filename": "avatar.png",
  "mime_type": "image/png",
  "size": 48213,
  "prog": "Rails",
  "req_id": "6f1c9a2e-7b4d-4e8a-9c61-2d5b8f0e4a17"
}

Log::CarrierWave::Upload src: carrierwave, evt: upload

{
  "src": "carrierwave",
  "evt": "upload",
  "lvl": "info",
  "ts": "2026-10-17T09:30:15.123+00:00",
  "storage": "file",
  "file_id": "avatar.png",
  "uploader": "AvatarUploader",
  "model": "User",
  "mount_point": "avatar",
  "version": "",
  "store_path": "uploads/user/avatar/1873/avatar.png",
  "ext": "png",
  "filename": "avatar.png",
  "mime_type": "image/png",
  "size": 48213,
  "duration_ms": 12.7,
  "prog": "Rails",
  "req_id": "6f1c9a2e-7b4d-4e8a-9c61-2d5b8f0e4a17"
}

`Log::Dotenv`

Log::Dotenv::Load src: dotenv, evt: load

{
  "src": "dotenv",
  "evt": "load",
  "lvl": "info",
  "ts": "2026-10-17T09:30:15.123+00:00",
  "file": ".env",
  "prog": "Rails"
}

Log::Dotenv::Restore src: dotenv, evt: restore

{
  "src": "dotenv",
  "evt": "restore",
  "lvl": "info",
  "ts": "2026-10-17T09:30:15.123+00:00",
  "vars": [
    "DATABASE_URL",
    "REDIS_URL"
  ],
  "prog": "Rails"
}

Log::Dotenv::Save src: dotenv, evt: save

{
  "src": "dotenv",
  "evt": "save",
  "lvl": "info",
  "ts": "2026-10-17T09:30:15.123+00:00",
  "snapshot": true,
  "prog": "Rails"
}

Log::Dotenv::Update src: dotenv, evt: update

{
  "src": "dotenv",
  "evt": "update",
  "lvl": "debug",
  "ts": "2026-10-17T09:30:15.123+00:00",
  "vars": [
    "DATABASE_URL",
    "REDIS_URL"
  ],
  "prog": "Rails"
}

`Log::Error`

Log::Error src: app, evt: error

{
  "src": "app",
  "evt": "error",
  "lvl": "error",
  "ts": "2026-10-17T09:30:15.123+00:00",
  "error_class": "JSON::ParserError",
  "msg": "Import failed",
  "error_message": "unexpected end of input",
  "backtrace": [
    "app/services/invoice_import.rb:27:in 'InvoiceImport#parse'",
    "app/controllers/imports_controller.rb:11:in 'ImportsController#create'"
  ],
  "prog": "Rails",
  "req_id": "6f1c9a2e-7b4d-4e8a-9c61-2d5b8f0e4a17"
}

`Log::GoodJob`

Log::GoodJob::Error src: job, evt: error

{
  "src": "job",
  "evt": "error",
  "lvl": "error",
  "ts": "2026-10-17T09:30:15.123+00:00",
  "error_class": "ActiveRecord::ConnectionNotEstablished",
  "error_message": "connection to server at \"10.0.3.12\", port 5432 failed: Connection refused",
  "pid": 4821,
  "tid": "2ix4",
  "backtrace": [
    "good_job/notifier.rb:225:in 'GoodJob::Notifier#with_connection'"
  ],
  "prog": "GoodJob"
}

Log::GoodJob::Log src: job, evt: log

{
  "src": "job",
  "evt": "log",
  "lvl": "info",
  "ts": "2026-10-17T09:30:15.123+00:00",
  "msg": "Notifier subscribed with LISTEN",
  "pid": 4821,
  "tid": "2ix4",
  "prog": "GoodJob"
}

`Log::Plain`

Log::Plain src: app, evt: log

{
  "src": "app",
  "evt": "log",
  "lvl": "info",
  "ts": "2026-10-17T09:30:15.123+00:00",
  "msg": "Exported 120 invoices",
  "prog": "Rails",
  "req_id": "6f1c9a2e-7b4d-4e8a-9c61-2d5b8f0e4a17"
}

`Log::Puma`

Log::Puma::Error src: puma, evt: error

{
  "src": "puma",
  "evt": "error",
  "lvl": "error",
  "ts": "2026-10-17T09:30:15.123+00:00",
  "error_class": "NoMethodError",
  "msg": "undefined method 'call' for nil",
  "backtrace": [
    "config/initializers/health_check.rb:8:in 'HealthCheck#call'"
  ],
  "error_context": "Rack app",
  "method": "GET",
  "path": "/up",
  "prog": "Rails"
}

Log::Puma::Shutdown src: puma, evt: shutdown

{
  "src": "puma",
  "evt": "shutdown",
  "lvl": "info",
  "ts": "2026-10-17T09:30:15.123+00:00",
  "pid": 1,
  "prog": "Rails"
}

Log::Puma::Start src: puma, evt: start

{
  "src": "puma",
  "evt": "start",
  "lvl": "info",
  "ts": "2026-10-17T09:30:15.123+00:00",
  "mode": "single",
  "puma_version": "6.6.1",
  "puma_codename": "Return to Forever",
  "ruby_version": "ruby 3.4.5 (2025-07-16 revision 20cda200d3) +PRISM [x86_64-linux]",
  "min_threads": 3,
  "max_threads": 3,
  "environment": "production",
  "pid": 1,
  "listening_addresses": [
    "http://0.0.0.0:3000"
  ],
  "prog": "Rails"
}

`Log::Request`

Log::Request src: rails, evt: request

{
  "src": "rails",
  "evt": "request",
  "lvl": "info",
  "ts": "2026-10-17T09:30:15.123+00:00",
  "path": "/users/sign_in",
  "method": "POST",
  "source_ip": "198.51.100.23",
  "user_agent": "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:131.0) Gecko/20100101 Firefox/131.0",
  "referer": "https://app.example.com/users/sign_in",
  "format": "html",
  "controller": "Users::SessionsController",
  "action": "create",
  "status": 302,
  "duration_ms": 48.21,
  "view": 0,
  "db": 3.62,
  "params": {
    "authenticity_token": "[FILTERED]",
    "user": {
      "email": "[FILTERED]",
      "password": "[FILTERED]",
      "remember_me": "1"
    },
    "commit": "Log in"
  },
  "host": "app.example.com",
  "content_type": "application/x-www-form-urlencoded",
  "accept": "text/html,application/xhtml+xml",
  "prog": "Rails",
  "req_id": "6f1c9a2e-7b4d-4e8a-9c61-2d5b8f0e4a17"
}

`Log::Security`

Log::Security::BlockedHost src: security, evt: blocked_host

{
  "src": "security",
  "evt": "blocked_host",
  "lvl": "warn",
  "ts": "2026-10-17T09:30:15.123+00:00",
  "path": "/",
  "method": "GET",
  "source_ip": "203.0.113.7",
  "user_agent": "curl/8.7.1",
  "msg": "Blocked host detected: admin.example.net",
  "blocked_host": "admin.example.net",
  "blocked_hosts": [
    "admin.example.net"
  ],
  "prog": "Rails"
}

Log::Security::CSRFViolation src: security, evt: csrf_violation

{
  "src": "security",
  "evt": "csrf_violation",
  "lvl": "error",
  "ts": "2026-10-17T09:30:15.123+00:00",
  "path": "/invoices/812",
  "method": "PATCH",
  "source_ip": "198.51.100.23",
  "user_agent": "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:131.0) Gecko/20100101 Firefox/131.0",
  "referer": "https://app.example.com/invoices/812/edit",
  "msg": "Can't verify CSRF token authenticity.",
  "prog": "Rails",
  "req_id": "6f1c9a2e-7b4d-4e8a-9c61-2d5b8f0e4a17"
}

Log::Security::IPSpoof src: security, evt: ip_spoof

{
  "src": "security",
  "evt": "ip_spoof",
  "lvl": "warn",
  "ts": "2026-10-17T09:30:15.123+00:00",
  "path": "/login",
  "method": "GET",
  "source_ip": "10.0.1.15",
  "user_agent": "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:131.0) Gecko/20100101 Firefox/131.0",
  "msg": "IP spoofing attack?! HTTP_CLIENT_IP=\"203.0.113.9\" HTTP_X_FORWARDED_FOR=\"198.51.100.4\"",
  "client_ip": "203.0.113.9",
  "x_forwarded_for": "198.51.100.4",
  "prog": "Rails",
  "req_id": "6f1c9a2e-7b4d-4e8a-9c61-2d5b8f0e4a17"
}

`Log::Shrine`

Log::Shrine::Delete src: shrine, evt: delete

{
  "src": "shrine",
  "evt": "delete",
  "lvl": "info",
  "ts": "2026-10-17T09:30:15.123+00:00",
  "storage": "store",
  "location": "invoice/812/original-3f9a1c.pdf",
  "prog": "Rails"
}

Log::Shrine::Download src: shrine, evt: download

{
  "src": "shrine",
  "evt": "download",
  "lvl": "info",
  "ts": "2026-10-17T09:30:15.123+00:00",
  "storage": "store",
  "location": "invoice/812/original-3f9a1c.pdf",
  "download_opts": {},
  "prog": "Rails",
  "req_id": "6f1c9a2e-7b4d-4e8a-9c61-2d5b8f0e4a17"
}

Log::Shrine::Exist src: shrine, evt: exist

{
  "src": "shrine",
  "evt": "exist",
  "lvl": "info",
  "ts": "2026-10-17T09:30:15.123+00:00",
  "storage": "store",
  "location": "invoice/812/original-3f9a1c.pdf",
  "prog": "Rails"
}

Log::Shrine::Metadata src: shrine, evt: metadata

{
  "src": "shrine",
  "evt": "metadata",
  "lvl": "info",
  "ts": "2026-10-17T09:30:15.123+00:00",
  "storage": "cache",
  "prog": "Rails",
  "req_id": "6f1c9a2e-7b4d-4e8a-9c61-2d5b8f0e4a17"
}

Log::Shrine::Upload src: shrine, evt: upload

{
  "src": "shrine",
  "evt": "upload",
  "lvl": "info",
  "ts": "2026-10-17T09:30:15.123+00:00",
  "storage": "store",
  "location": "invoice/812/original-3f9a1c.pdf",
  "upload_opts": {},
  "opts": {},
  "uploader": "DocumentUploader",
  "duration_ms": 143.8,
  "prog": "Rails",
  "req_id": "6f1c9a2e-7b4d-4e8a-9c61-2d5b8f0e4a17"
}

`Log::Sidekiq`

Log::Sidekiq::Error src: sidekiq, evt: error

{
  "src": "sidekiq",
  "evt": "error",
  "lvl": "warn",
  "ts": "2026-10-17T09:30:15.123+00:00",
  "error_class": "Timeout::Error",
  "msg": "execution expired",
  "backtrace": [
    "app/workers/invoice_sync_worker.rb:15:in 'InvoiceSyncWorker#perform'"
  ],
  "error_context": "Job raised exception",
  "queue_name": "default",
  "retry_count": 2,
  "prog": "Rails",
  "ctx": {
    "jid": "b4a9c63e5f1d2a7e9c0f3b18",
    "class": "InvoiceSyncWorker"
  }
}

Log::Sidekiq::Log src: sidekiq, evt: log

{
  "src": "sidekiq",
  "evt": "log",
  "lvl": "info",
  "ts": "2026-10-17T09:30:15.123+00:00",
  "msg": "start",
  "ctx": {
    "jid": "b4a9c63e5f1d2a7e9c0f3b18",
    "class": "InvoiceSyncWorker"
  },
  "pid": 4821,
  "tid": "1v8b",
  "prog": "Sidekiq-Server"
}

`Log::SQL`

Log::SQL src: app, evt: database

{
  "src": "app",
  "evt": "database",
  "lvl": "info",
  "ts": "2026-10-17T09:30:15.123+00:00",
  "msg": "Invoice Load executed",
  "sql": "SELECT \"invoices\".* FROM \"invoices\" WHERE \"invoices\".\"account_id\" = $1",
  "name": "Invoice Load",
  "duration_ms": 142.37,
  "row_count": 120,
  "adapter": "PostgreSQLAdapter",
  "db_name": "app_production",
  "pool_size": 5,
  "active_count": 2,
  "op_type": "SELECT",
  "table_names": [
    "invoices"
  ],
  "prog": "Rails",
  "req_id": "6f1c9a2e-7b4d-4e8a-9c61-2d5b8f0e4a17"
}

Value Formats

Timestamps

ts is an ISO 8601 time with milliseconds and the UTC offset of the process's time zone: 2026-10-17T09:30:15.123+00:00 on a server whose time zone is UTC, 2026-10-17T22:30:15.123+13:00 on one in New Zealand. Rails' config.time_zone doesn't change it. Every other time in a line is written the same way: the times of the built-in log types, such as ActiveJob's scheduled_at, and the times in a Hash you log.

Levels

lvl is debug, info, warn, error, fatal or unknown. It comes from the logger method that wrote the line (logger.warn writes warn), not from the log type's own level. Any other severity is written as unknown.

Filtered Values

A value whose key is filtered is replaced by a summary under _filtered. Which keys are filtered is described in Filtering Sensitive Data.

Rails.logger.info(
  msg: "Account updated",
  email: "linda.martinez@example.com",
  password: "correct horse battery staple",
  api_tokens: ["tok_8c1f2a", "tok_93d0b7"],
  credentials: {client_id: "my-app", client_secret: "abc123"},
  note: "Call Linda on 555-201-7788"
)

{
  "msg": "Account updated",
  "email": {
    "_filtered": {
      "_class": "String",
      "_hash": "a058d5090035d2e1"
    }
  },
  "password": {
    "_filtered": {
      "_class": "String"
    }
  },
  "api_tokens": {
    "_filtered": {
      "_class": "Array",
      "_count": 2
    }
  },
  "credentials": {
    "_filtered": {
      "_class": "Hash",
      "_keys_count": 2,
      "_keys": [
        "client_id",
        "client_secret"
      ]
    }
  },
  "note": "Call Linda on [PHONE]",
  "src": "app",
  "evt": "log",
  "ts": "2026-10-17T09:30:15.123+00:00",
  "lvl": "info",
  "prog": "Rails"
}

A String: {"_class": "String"}, without its length. For keys in filter_keys_with_hashes (email and email_address by default) the summary also has a _hash of the value: 16 hex characters of an HMAC-SHA256 keyed with filters.hash_salt, or by default with a key derived from the app's secret_key_base. An email address has one hash however it's capitalized.
A Hash: _class, _keys_count and its first 10 keys in _keys. An empty Hash is {"_class": "Hash", "_empty": true}.
An Array: _class and _count. An empty Array is {"_class": "Array", "_empty": true}.
Any other value: its class, such as {"_class": "Integer"}.
A value that Rails' filter_parameters already replaced, such as the params on request lines, is kept as Rails wrote it: "[FILTERED]".
Values nested more than 20 levels deep, and values that contain themselves, are written as a summary without _keys.

Scrubbed strings keep their text, with the sensitive part replaced: [EMAIL:<hash>] (the same hash as _hash above), [PHONE], [SSN], [CREDIT_CARD], [PASSWORD] for a password in a URL, and [FILTERED] for the credentials after Bearer or Basic and sensitive query params. [IP] and [MAC] appear only when you turn those scrubbers on.

Truncation

config.limits sets how much of each value LogStruct writes:

max_hash_keys (default 100): a Hash writes its first 100 keys, then _more_keys with the number left out. The line's own keys count too.
max_array_items (default 10): an Array writes its first 10 items, then a last item "... and N more items".
max_backtrace_lines (default 20): for an Array that looks like a backtrace (3 of its first 5 items start with file:line), such as an error line's backtrace, the first 20 lines, then "... and N more lines".
max_string_bytes (default 32768, 32 KB): a longer string is cut to that many bytes after it's scrubbed, and ends with "... (cut from N bytes)".

# Small limits, to show the markers (the defaults are 100 keys, 10 items and 32 KB).
# A line's own keys count too: this one has 4.
LogStruct.configure do |config|
  config.limits.max_hash_keys = 4
  config.limits.max_array_items = 3
  config.limits.max_string_bytes = 24
end

Rails.logger.info(
  msg: "Import finished",
  columns: {first_name: "First name", last_name: "Last name", city: "City", country: "Country", zip: "Postcode"},
  row_ids: [101, 102, 103, 104, 105, 106, 107, 108],
  summary: "Rows 104 and 107 had no postcode"
)

{
  "msg": "Import finished",
  "columns": {
    "first_name": "First name",
    "last_name": "Last name",
    "city": "City",
    "country": "Country",
    "_more_keys": 1
  },
  "row_ids": [
    101,
    102,
    103,
    "... and 5 more items"
  ],
  "summary": "Rows 104 and 107 had no ... (cut from 32 bytes)",
  "src": "app",
  "evt": "log",
  "ts": "2026-10-17T09:30:15.123+00:00",
  "lvl": "info",
  "prog": "Rails"
}

The settings on this page are described in Configuration.

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