HOI4 Modding Research Slots: 2026 Guide

Hearts of Iron IV modding in 2026 lets you expand research slots beyond vanilla limits. This step-by-step tutorial covers file edits, scripting, and testing for custom nations.

Step 1: Tools and Setup

Prepare mod environment.

  • 1. Install HOI4 1.14+
  • 2. Use Notepad++ for files
  • 3. Create mod folder in Documents

Step 2: Editing country.txt

Add extra slots via script.

  • 1. Open /common/countries/
  • 2. Add research_slots = 5
  • 3. For dynamic: scripted_effect

Step 3: Ideas and Technologies

Link to ideas for bonuses.

  • 1. Define idea with slot +1
  • 2. Trigger via focus tree
  • 3. Balance with costs

Step 4: UI Modifications

Update interface files.

  • 1. Edit interface/research.gui
  • 2. Add slot widgets
  • 3. Test in-game

Step 5: Testing and Validation

Ensure no crashes.

  • 1. Run -debug mode
  • 2. Check log.txt
  • 3. Steam Workshop upload

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