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Templates

Templates

Overview

You can customize the message posted by setting a notification template.

Notification Template

Sets the Go template used for formatting notification messages.

            Argument: --notification-template
Environment Variable: WATCHTOWER_NOTIFICATION_TEMPLATE
                Type: String
             Default: See default templates below

Notification Template File

Sets the path to a file containing the Go template used for formatting notification messages.

            Argument: --notification-template-file
Environment Variable: WATCHTOWER_NOTIFICATION_TEMPLATE_FILE
                Type: String
             Default: (empty)

When both the notification-template and notification-template-file configuration options are specified, the file-based template takes precedence over the inline template.

Examples

Create a template file named custom-template.txt with your desired template content, then mount it into the container and specify the path:

services:
    watchtower:
        image: nickfedor/watchtower:latest
        environment:
            WATCHTOWER_NOTIFICATION_TEMPLATE_FILE: "/custom-template.txt"
        volumes:
            - /var/run/docker.sock:/var/run/docker.sock
            - /path/to/custom-template.txt:/custom-template.txt

Notification Report

Enables the session report as the notification template data, including container statuses and logs.

            Argument: --notification-report
Environment Variable: WATCHTOWER_NOTIFICATION_REPORT
                Type: Boolean
             Default: false

The template is a Go template that processes either a list of log entries (Message, Data, Level, Time) captured from zerolog events or a notifications.Data struct, depending on the notification-report configuration option.

Simple Templates

Simple templates are used when the notification-report configuration option is not set, formatting individual log entries as they occur.

{{- range $i, $e := . -}}
{{- if $i}}{{- println -}}{{- end -}}
{{- $msg := $e.Message -}}
{{- if eq $msg "Found new image" -}}
    Found new image: {{$e.Data.image}} ({{with $e.Data.new_id}}{{.}}{{else}}unknown{{end}})
{{- else if eq $msg "Stopping container" -}}
    Stopped stale container: {{$e.Data.container}} ({{with $e.Data.id}}{{.}}{{else}}unknown{{end}})
{{- else if eq $msg "Started new container" -}}
    Started new container: {{$e.Data.container}} ({{with $e.Data.new_id}}{{.}}{{else}}unknown{{end}})
{{- else if eq $msg "Removing image" -}}
    Removed stale image: {{with $e.Data.image_id}}{{.}}{{else}}unknown{{end}}
{{- else if eq $msg "Detected multiple Watchtower instances - initiating cleanup" -}}
    Detected {{$e.Data.count}} Watchtower instances - initiating cleanup
{{- else if $e.Data -}}
    {{$msg}} | {{range $k, $v := $e.Data -}}{{$k}}={{$v}} {{- end}}
{{- else -}}
    {{$msg}}
{{- end -}}
{{- end -}}
  • This template processes info-level log entries in real-time, formatting key update events in past tense with container and image details from structured log fields.
  • It sends each event immediately in legacy mode, mimicking a step-by-step log.

Using Simple Templates in the Preview Tool

The Template Preview Tool uses a notifications.Data struct with .Entries as the log list.

To use the simple template in the preview tool, modify the range to {{- range $i, $e := .Entries -}} to match the data structure.
{{- range $i, $e := .Entries -}}
{{- if $i}}{{- println -}}{{- end -}}
{{- $msg := $e.Message -}}
{{- if eq $msg "Found new image" -}}
    Found new image: {{$e.Data.image}} ({{with $e.Data.new_id}}{{.}}{{else}}unknown{{end}})
{{- else if eq $msg "Stopping container" -}}
    Stopped stale container: {{$e.Data.container}} ({{with $e.Data.id}}{{.}}{{else}}unknown{{end}})
{{- else if eq $msg "Started new container" -}}
    Started new container: {{$e.Data.container}} ({{with $e.Data.new_id}}{{.}}{{else}}unknown{{end}})
{{- else if eq $msg "Removing image" -}}
    Removed stale image: {{with $e.Data.image_id}}{{.}}{{else}}unknown{{end}}
{{- else if eq $msg "Detected multiple Watchtower instances - initiating cleanup" -}}
    Detected {{$e.Data.count}} Watchtower instances - initiating cleanup
{{- else if $e.Data -}}
    {{$msg}} | {{range $k, $v := $e.Data -}}{{$k}}={{$v}} {{- end}}
{{- else -}}
    {{$msg}}
{{- end -}}
{{- end -}}

Example output for a log entry with msg="Found new image":

Found new image: repo/image:latest (abcdef123456)

Report Templates

When the notification-report configuration option is set, the template processes a notifications.Data struct containing a session report and log entries.

{{- if .Report -}}
  {{- with .Report -}}
    {{len .Scanned}} Scanned, {{len .Updated}} Updated, {{len .Restarted}} Restarted, {{len .Failed}} Failed
    {{- if ( or .Updated .Restarted .Failed ) -}}
      {{- range .Updated}}
- {{.Name}} ({{.ImageName}}): {{.CurrentImageID.ShortID}} updated to {{.LatestImageID.ShortID}}
      {{- end -}}
      {{- range .Fresh}}
- {{.Name}} ({{.ImageName}}): {{.State}}
      {{- end -}}
      {{- range .Restarted}}
- {{.Name}} ({{.ImageName}}): {{.State}}
      {{- end -}}
      {{- range .Skipped}}
- {{.Name}} ({{.ImageName}}): {{.State}}: {{.Error}}
      {{- end -}}
      {{- range .Failed}}
- {{.Name}} ({{.ImageName}}): {{.State}}: {{.Error}}
      {{- end -}}
    {{- end -}}
  {{- end -}}
{{- if .Entries -}}

Logs:
{{- end -}}
{{range .Entries -}}{{.Time.Format "2006-01-02T15:04:05Z07:00"}} [{{.Level}}] {{.Message}}{{"\n"}}{{- end -}}
{{- end -}}
  • This template generates a summary of container statuses (scanned, updated, failed, etc.) followed by logs, used for notifications like email or Slack messages.

Example Usage 

services:
    watchtower:
        image: nickfedor/watchtower:latest
        volumes:
            - /var/run/docker.sock:/var/run/docker.sock
        environment:
            WATCHTOWER_NOTIFICATION_REPORT: "true"
            WATCHTOWER_NOTIFICATION_URL: >
                discord://token@channel
                slack://watchtower@token-a/token-b/token-c
            WATCHTOWER_NOTIFICATION_TEMPLATE: |
                {{- if .Report -}}
                {{- with .Report -}}
                {{len .Scanned}} Scanned, {{len .Updated}} Updated, {{len .Restarted}} Restarted, {{len .Failed}} Failed
                {{- if ( or .Updated .Restarted .Failed ) -}}
                    {{- range .Updated -}}
                - {{.Name}} ({{.ImageName}}): {{.CurrentImageID.ShortID}} updated to {{.LatestImageID.ShortID}}
                    {{- end -}}
                    {{- range .Fresh -}}
                - {{.Name}} ({{.ImageName}}): {{.State}}
                    {{- end -}}
                    {{- range .Restarted -}}
                - {{.Name}} ({{.ImageName}}): {{.State}}
                    {{- end -}}
                    {{- range .Skipped -}}
                - {{.Name}} ({{.ImageName}}): {{.State}}: {{.Error}}
                    {{- end -}}
                    {{- range .Failed -}}
                - {{.Name}} ({{.ImageName}}): {{.State}}: {{.Error}}
                    {{- end -}}
                {{- end -}}
                {{- end -}}
                {{- if .Entries -}}

                Logs:
                {{- end -}}
                {{- range .Entries -}}{{.Time.Format "2006-01-02T15:04:05Z07:00"}} [{{.Level}}] {{.Message}}{{"\n"}}{{- end -}}
                {{- end -}}

Example output for a session with one updated container, one restarted container, and one error log:

5 Scanned, 1 Updated, 1 Restarted, 0 Failed
- /container (repo/image:latest): abcdef12 updated to 34567890
- /restarted-container (repo/image:latest): Restarted

Logs:
2025-08-20T06:00:13-07:00 [error] Operation failed. Try again later.

Customizing Templates

You can create custom templates to format notifications differently.

Use the Template Preview Tool to test your templates interactively.

When testing simple templates in the preview tool, ensure the range iterates over .Entries (e.g., {{- range $i, $e := .Entries -}}) to match the notifications.Data struct.

Additional Resources

  • For detailed template syntax, refer to the Go Template documentation.
  • For log entry fields, each entry exposes Message, Data (map of structured fields), Level, and Time (see pkg/notifications notification entries and zerolog).
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