Performance

The Need for Speed

Picture the climactic battle with the dragon. The music swells, dice are ready, players lean in... and the map freezes. Nothing breaks immersion faster than lag. Good performance isn't about owning the fastest computer; it's about making sensible choices with your maps, lights, sounds and modules so the game keeps flowing.

Foundry runs in a browser on every player's machine, while your host (your own computer or a hosting service) sends everyone the world data and files. A slow game can come from either end, so it helps to know where the costs actually are.

Where Performance Goes

Official Minimum Requirements

Start by checking that every machine at the table meets Foundry's published requirements. A player on hardware below the minimum will struggle no matter how lean your scenes are.

The single most common cause of a "Foundry is slow for one player" report is a browser with hardware acceleration switched off. In Chrome, Edge and Opera it's in the browser's system settings ("Use graphics acceleration when available"); in Firefox it's under performance settings. Foundry may also show a warning when it can't use the graphics card.

Scene Optimization Techniques

Scenes are where most of the cost lives. Big images take longer to download and fill graphics memory; every light, vision source and wall adds work for each player's graphics card.

Lighting and Vision

• Lights: each light source has to be drawn and blocked by walls. Use lights where they matter for the story or tactics, and lean on the scene's global illumination or darkness level for general brightness.
• Vision: every token with vision enabled has its sight calculated against the walls. Player-controlled tokens need it; most NPC tokens don't, because the GM sees everything anyway.
• Walls: trace rooms with sensible, longer segments. Hundreds of tiny segments on a curved cave wall add calculation work without making play better.
• Scene Levels: V14 lets one scene hold several floors. That's convenient, but every level's images, lights and walls belong to the same scene, so a five-storey tower is heavier than a single floor. Split very large buildings into separate scenes if players struggle.
• Animated effects: animated lights, weather and video tiles redraw constantly. Use them for set pieces, not every scene.

Image, Video and Audio Formats

Foundry's own guidance is simple: WebP for images, WebM for video and animated maps, OGG for audio. These formats are well compressed and well supported by the browsers Foundry runs in.

Quick Asset Checklist

• Size maps to what you actually play on. A 30 × 20 square map at 100 pixels per square is 3000 × 2000 pixels; anything much larger is downloaded but never seen.
• Convert images to WebP (with a tool such as Squoosh or your image editor's export).
• Convert animated maps and video tiles to WebM, and audio to OGG.
• Very large images can exceed what some graphics cards can hold as a single texture; split huge maps into several tiles or scenes instead.
• Keep token art small; tokens are shown at a fraction of a map square.

Module Performance Impact

Modules load for every player. Disable what you aren't using, and see Modules & Add-ons for how to find a module that's causing trouble.

For example, Dice So Nice! renders 3D dice and Token Magic FX applies graphics filters, so both lean on the graphics card; players on weaker machines can usually turn the effects down in their own client settings.

Hosting and Network

When you self-host, every player downloads every map, token and sound from your internet connection. Your upload speed, not your download speed, is what matters, and it's shared among all players. A large map that takes one player a few seconds to download takes longer when five people request it at once.

Performance Settings Deep Dive

Foundry has one core setting built for this: Performance Mode, in Configure Settings, which ranges from Low to Maximum. It's a per-client setting, so each player picks the level their own machine can handle. Lower modes trade some visual quality for smoother play.

Try It in Foundry: Performance Audit

Troubleshooting Performance Issues

Common Problems and Solutions

• Choppy movement for one player:
  • Check hardware acceleration and browser choice.
  • Lower that player's Performance Mode.
  • Ask them to turn down module effects in their own settings.
• Slow loading for everyone:
  • Shrink and convert large assets.
  • Check the host's upload speed, or move to a hosting partner.
  • Preload scenes before switching.
• Slowdown that appeared after an update:
  • Launch in Safe Configuration to rule modules in or out.
  • Use Find the Culprit! to identify the module.
  • Check that module's issue tracker for a fix.
• Gets worse over a long session:
  • Reload the browser tab (F5) during a break.
  • Check the console (F12) for repeating errors.

Performance Best Practices

The Golden Rules

1. Start simple: add complexity gradually.
2. Test with players: your own machine is not the weakest at the table.
3. Measure first: find the actual bottleneck before changing things.
4. Serve the game: effects should support play, not slow it.
5. Write it down: keep notes on what helped.

Session Preparation

• Preload the first scenes before players arrive.
• Have a lighter fallback version of any very heavy scene.
• Test a new scene with one player before the full group.
• Update Foundry and modules days before a session, not minutes before, and take a backup first.

Three Common Fixes

The Oversized Battle Map

A GM imports a battle map at its full print resolution and players complain of slow loading and stuttering. Resizing it to match the grid, saving it as WebP, and removing lights that only decorated empty corners keeps the same look with far less work for every machine.

The Module Pile-Up

After a year of "just one more module," a world takes a long time to load. Going through Manage Modules, disabling everything unused, and checking the rest with Find the Culprit! brings it back to a manageable set.

The One Laggy Player

One player's view lags while everyone else is fine. The cause is often on their side: Safari, hardware acceleration off, or a busy Wi-Fi connection. A supported browser with acceleration on, plus a lower Performance Mode, usually solves it.

What's Next?

You now know where Foundry spends its effort and how to keep scenes, assets, modules and hosting lean, so the technology stays in the background and the story stays in front.

Next up is Advanced GM Techniques.