Data File

File Extension: .esm, .esp, .esl, .fos

A Data File acts as a database of all of the data for the world, including object data, dialogue, gameplay settings, object placements, AI settings, landscape, cells, etc.

Files

There are three types of data files -- Master Files and Plugin Files, and new as of the 1.10 Update, Light Plugin files. Master files and plugins (normal and Light) are largely identical in format, but have some important distinctions in practice.

Master: .esm

• A master file is autonomous; it relies on no information other than itself.
  • The Creation Kit will not create master files.
    • NOTE: An exception to this rule is when using the Creation Kit's built in version control system. The merging process takes the interim esp data and merges into a master file to be used by the collaborators. See this page for details Version Control and Multiple Contributor Collaboration

Plugin: .esp

• A plugin ESP file may only rely on data from itself and any master ESM files.
  • Plugins are not required to contain any data.
  • Plugins are not required to have a master if they are empty or add new content.
  • Plugins can only refer directly to data from a master file, though they can refer to multiple master files.
  • Plugins can only refer to information in another plug-in indirectly by using scripts.

Light Master: .esl

• Light plugin (.esl) file are a new optimized file format, introduced in the 1.10 Update. They behave like a normal plugin, except for the following:
  • .esl files are read-only. Active development should be done in an normal (.esp) plugin.
  • .esl files bypass the 8-bit plugin ID limit (255).
  • .esl files have a budget of no more than 4,000 forms.
  • .esl files are treated as unique files from the .esp it was converted from, so saved games will not be compatible between them.
• To convert a normal plugin (.esp) to a light (.esl) plugin, load your .esp file, and under File, select Convert Active File to Light Master.
• It is good practice to run Compact Active File Form IDs to optimize your formids within the 4,000 form budget.
  • NOTE: Compacting form ids does change formids in the plugin, so only do this before converting to .esl, and not on a .esp (plugin) you plan on releasing.

Save: .fos

• A Fallout Save (.fos) is used to restore the games state between sessions.
  • The Creation Kit will not create, edit or view save files.

Tooling

• The Creation Kit is the primary tooling for working with data files.
• FO4Edit
• There are other community software projects that provided tooling for working with data files.

Notes

• By tradition, the file extensions stand for Elder Scrolls Master and Elder Scrolls Plugin.
• While not directly supported, a .esl can be converted back to a .esp for editing in one of the following ways.
  1. Rename the file back to .esp. Open it for editing with FO4Edit, and in the Header section edit the flags to trigger a resave. Simply choosing the ESM flag on and off again will suffice. Then save. It will then be binary identical to the original .esp it was created from.
  2. With the current version of the Creation Kit (1.10 at time of writing) you can also simply rename the .esl to .esp and open it. The Creation Kit will identify it as a plugin ignoring the header flag and allow editing. When You are finished you just save like normal. If you save as a normal .esp the header is automatically converted back to that of a standard plugin. You may use the convert to .esl function to publish the file as a .esl master again. This behavior may change in the future.

See Also

• Game Files Category