# Templates User Guide

Open **Templates** to create or select a reusable definition.

1. Choose the template type and the contexts in which it may be used, such as
   `campaign.postal`.
2. Declare every required input path and its type. Use the same paths as tokens
   in the body, for example `{{name}}` or `{{postal.address}}`.
3. Configure page size and, for label sheets, rows, columns, and spacing.
4. Save to create a new immutable revision. Publish the revision before using
   it for final output.
5. In **Preview**, supply a representative JSON item. Compatibility validation
   explains missing fields, wrong types, unsupported usages, and output-format
   mismatches before output is produced.
6. Preview a draft or render final output. Store it in Files when that module is
   available and you have upload permission; otherwise use the bounded download.
   Bounded output history is visible only to the actor who rendered it and to a
   Templates administrator. Calling modules expose their own governed download
   when additional collaborators need access.

Render evidence shows the exact revision and abbreviated template, input, and
output hashes. A consumer such as Campaign can submit many frozen recipients;
the UI sample intentionally validates one representative item.

Rendering is also limited to 15 seconds elapsed time, 10 CPU seconds, 512 MiB
process memory, 32 MiB serialized input and 8 MiB serialized result transport;
the final output remains limited to 5 MiB and 5,000 items. Deeply nested data
or more than 1,000,000 transported value nodes is rejected. A limit error creates
no partial output or render evidence: reduce the selected input or template
complexity and retry. If processing capacity is busy, retry later. Unavailable
worker controls or a worker failure require operator investigation. Existing
successful output with the same idempotency key is reused without rendering
again, provided its input and authorization still match.