Preview

The preview surface runs in dev and uses your production render pipeline, so HTML/Text/Raw/Headers stay consistent with real delivery.

The screenshot capture workflow is for preview-pipeline confidence only. It does not claim cross-client parity across Outlook/Gmail/Apple Mail.

Prerequisites

• mailglass_admin dependency available in :dev
• Router mounted behind your dev-only routes

Mount preview routes

defmodule MyAppWeb.Router do
  use Phoenix.Router
  import MailglassAdmin.Router

  if Application.compile_env(:my_app, :dev_routes) do
    scope "/dev" do
      pipe_through :browser
      mailglass_admin_routes "/mail"
    end
  end
end

Start and open preview

mix phx.server
# open http://localhost:4000/dev/mail

Add preview props on a mailable

defmodule MyApp.UserMailer do
  use Mailglass.Mailable, stream: :transactional

  @impl Mailglass.Mailable
  def preview_props do
    [name: "Alice", email: "alice@example.com"]
  end
end

End-to-End Example

mix phx.server

Deterministic capture workflow

Use one maintainer command to capture a deterministic screenshot matrix from the same /dev/mail preview route:

cd mailglass_admin
mix mailglass_admin.preview.capture \
  --base-url http://localhost:4000/dev/mail \
  --output-dir tmp/mailglass_admin_preview_capture

Default matrix dimensions:

• Widths: 375, 768, 1024
• Themes: light, dark
• Scenarios: discovered from each mailable's preview_props/0

Dry-run before capture

Dry-run prints the matrix and still writes deterministic contract artifacts:

cd mailglass_admin
mix mailglass_admin.preview.capture \
  --dry-run \
  --base-url http://localhost:4000/dev/mail \
  --output-dir tmp/mailglass_admin_preview_capture

Artifact contract

The command writes:

• tmp/mailglass_admin_preview_capture/<mailable>--<scenario>--w<width>--<theme>.png
• tmp/mailglass_admin_preview_capture/manifest.json
• tmp/mailglass_admin_preview_capture/checkpoint.json

manifest.json and checkpoint.json use schema version preview_capture.v1 and include bounded language: preview-pipeline confidence only; not cross-client parity.