Catalog Formats

Palamedes catalogs are source-string-first. The semantic message identity is message + context; compiled lookup keys remain an internal runtime detail.

Palamedes currently exposes two catalog storage formats:

Format	Extension	Best fit
PO	`.po`	Default, translator-friendly gettext-style files and current app imports
FCL	`.fcl`	Canonical Ferrocat Catalog Lines for generated, merge-friendly storage

PO

PO is the default because it is familiar, human-editable, and supported by the current Vite and Next loader paths. A minimal config does not need a format field:

locales: [en, de]
source-locale: en
catalogs:
  - path: src/locales/{locale}
    include: [src]

That writes src/locales/en.po and src/locales/de.po.

FCL

FCL means Ferrocat Catalog Lines. It is a line-oriented Ferrocat catalog format that Palamedes treats as canonical generated storage. Use it when the catalog files are mostly maintained by pmds extract, merge drivers, or automation rather than hand-edited as gettext PO files.

Opt in per catalog:

locales: [en, de]
source-locale: en
catalogs:
  - path: src/locales/{locale}
    format: fcl
    include: [src]

That writes src/locales/en.fcl and src/locales/de.fcl.

FCL is not NDJSON. The older ndjson config value is intentionally rejected; use format: fcl instead.

For existing projects moving from old NDJSON catalog settings, see Migrating to Palamedes 1.0.

Runtime Loading

Catalog storage and framework module loading are related but separate:

pmds extract, pmds audit, pmds catalog merge, and native compile APIs understand both PO and FCL through the Palamedes config.
The current first-party Vite and Next import loaders are still .po import loaders. Keep app-facing imports on PO unless the host adapter explicitly documents FCL imports.
pmds catalog convert can write .fcl files beside existing .po files so teams can trial FCL storage before changing config.

Converting Existing Catalogs

Convert one catalog:

pmds catalog convert src/locales/de.po --to fcl --output src/locales/de.fcl

Convert every configured PO catalog:

pmds catalog convert --config palamedes.yaml --to fcl

After conversion, update the matching catalog config to format: fcl.

The full 1.0 migration checklist, including merge-driver cleanup and metadata shape changes, lives in Migrating to Palamedes 1.0.