The complete guide · 5 min read
Arma 3 Headless Client Server Hosting: The Complete Guide
Every Arma 3 unit that runs AI-heavy co-op eventually meets the same problem: the server's frame rate drops as the mission fills with enemies, and everything starts to feel sluggish. A headless client is Bohemia's answer. This guide explains what it does, when it helps, how to connect it, what your mission needs and how to size it.
By Matthew Griffin, Owner, Gaming DeluxePublished · Updated
In this guide
- Why AI Slows an Arma 3 Server
- What a Headless Client Does
- Connecting It to Your Server, Step by Step
- Getting the Mission Ready
- Sizing: Memory, CPU and When to Add a Second One
- Fitting a Headless Client Into Your Unit's Routine
- When the Headless Client Does Nothing
- What to Compare Before Renting a Headless Client
- Arma 3 Headless Client Glossary
- Headless Client Help and Next Steps
Why AI Slows an Arma 3 Server
In Arma 3, AI is simulated by the machine that owns it. On a normal dedicated server, that is the server itself. Every patrol, every garrison and every squad that reacts to contact adds work the server has to finish on every frame, next to player movement, vehicles, physics and mission scripts. On a busy co-op op, the AI usually becomes the largest share of that work.
When the server cannot keep up, its frame rate falls. Players see AI that react late, vehicles that stutter and hit registration that feels off. Adding memory rarely helps, because the bottleneck is processing, not space. Moving the AI to another machine does.
What a Headless Client Does
A headless client is a copy of Arma 3 with no screen and no player. It connects to your server like any other client, takes a Headless Client slot in the mission, and then owns whatever AI the mission or a mod hands to it. The server still runs the mission, but the AI's thinking happens on the headless client.
- The main server keeps players, mission logic and scripts.
- The headless client runs the AI groups given to it.
- Several headless clients can split the AI between them on big missions.
- Nothing changes for players: they join the main server as normal.
Connecting It to Your Server, Step by Step
Our knowledge base guide follows this order, and it is worth doing exactly so, because a missing line on either side is the usual reason a headless client does not appear.
- Stop the main server and open server.cfg under Configuration Files.
- Enter the headless client's IP address in both headlessClients[] and localClient[]. For several headless clients, list each IP, separated by commas, in both lines.
- Stop the headless client server and open its Start.bat under Configuration Files.
- Enter the main server's IP in the connect field, and the main server's password in the password field if it has one.
- Start the main server, then the headless client. It appears in the player list like any other client.
The first line lets the headless client join; the second treats it as a local client, without the bandwidth limits applied to normal players. Both are needed.
Getting the Mission Ready
The mission needs a seat for the headless client. In the Eden editor, place a unit from Game Logic, Virtual Entities, Headless Client, set it to Playable and give it a name. Bohemia's update 2.22 added a server log warning when this slot has no name, because an unnamed slot cannot be used.
Then something has to hand the AI over. Many unit missions spawn their AI on the headless client directly or move groups across when it connects. Some AI mods and frameworks do this on their own once they detect a headless client. Altis Life, for example, ships a headless client addon and a HeadlessSupport switch in its description.ext. Each project has its own instructions, and our knowledge base links to Bohemia's documentation and community guides for the common setups.
Sizing: Memory, CPU and When to Add a Second One
| Mission style | Suggested plan | Notes |
|---|---|---|
| Light co-op with a few patrols | 5GB | Vanilla or lightly modded |
| Weekly ops with steady AI | 8GB | Where most units start |
| Dynamic missions with waves | 12GB | More AI and AI mods |
| Large terrains, heavy mod sets | 16GB | Or split across two headless clients |
Because AI is processor work, a single very busy headless client can become the next bottleneck. If one is maxed out while the main server has recovered, a second headless client often helps more than extra memory. Faster CPUs and higher CPU priority are also on the order form for AI-heavy missions.
Fitting a Headless Client Into Your Unit's Routine
Most units run the same rhythm every week: mission makers prepare an op, the server is updated and restarted, players load in, and the op runs for a couple of hours. A headless client slots into that rhythm with a few habits.
- Restart together: schedule the headless client's restart a minute after the main server's, so it reconnects once the mission is up.
- Update together: when Bohemia releases an update or you change the mod set, update both servers before op night, not during it.
- Test in the editor flow: mission makers should check the Headless Client slot is named and playable before a mission is uploaded.
- Keep notes: write down which missions use the headless client and how, so new mission makers follow the same pattern.
- Watch op night: keep an eye on server FPS during the first op with the headless client, and compare it with an op without one.
Units that run several missions in rotation often find that only some of them are AI-heavy enough to need a headless client. That is fine: a connected headless client with nothing to do costs the main server almost nothing, and it is ready the moment a mission hands it work.
When the Headless Client Does Nothing
- Not in the player list: check both lines in the main server's server.cfg and the IP and password in Start.bat.
- Connected but idle: check the mission has a named, playable Headless Client slot, and that a script or mod hands AI to it.
- Kicked on join: the headless client is missing a mod or is on another build; update both and match the mods.
- No improvement: look at whether the AI really moved; the log viewer and your mission's debug tools will show it.
Our support team can look at the logs on both servers with you. It also helps to have the main server and headless client in the same location, so the link between them is short and stable.
What to Compare Before Renting a Headless Client
Few hosts sell a headless client as its own product. Compare them on these points.
- Same location as your serverThe headless client should sit next to your main server.
- Start-up controlYou need to set the connect address and password yourself.
- Memory choicePlans should scale with your AI load, not force one size.
- CPU optionsAI is processor work, so faster cores or priority matter.
- Support that knows ArmaAsk whether support can help with the mission side, not just the connection.
- Monthly priceCompare the memory you need on the same billing term.
Arma 3 Headless Client Glossary
- Headless client (HC)
- An Arma 3 instance with no screen that joins a server to run AI.
- headlessClients[]
- The server.cfg line listing IPs allowed to join as headless clients.
- localClient[]
- The server.cfg line that treats those IPs as local, without bandwidth limits.
- Start.bat
- The headless client's start-up file, with its connect and password fields.
- Headless Client slot
- The playable, named Virtual Entities unit a mission needs for an HC to join.
- Server FPS
- How many simulation frames the server completes per second.
- Offloading
- Moving AI ownership from the server to a headless client.
Headless Client Help and Next Steps
Guides and related servers.
- How to set up your Headless Client serverServer.cfg, Start.bat and the mission side.
- Arma 3 Server HostingThe main server your headless client connects to.
- Arma 3 server setup guideServer.cfg, missions, mods and the headless client in one place.
- Contact supportHelp connecting the headless client, day or night.
How this guide was made: researched from Bohemia Interactive's Arma 3 pages, the Arma 3 dev hub update notes and our own Headless Client knowledge base guide, drafted with AI assistance, checked against our live order form for every plan, price and location, and reviewed by Matthew Griffin before publishing. Spotted something out of date? Tell us.
Sources, checked 23 October 2026:
- Arma 3 on Steam (Bohemia Interactive, 12 September 2013)
- Arma 3 dev hub: SPOTREP #00120, Game Update 2.22 (11 August 2026: Headless Client slot warning, netcode, idleFPSLimit)
- Bohemia Interactive wiki: Arma 3 Headless Client (blocks automated reads; facts taken via our Arma 3 setup guide's archived copy)
- Gaming Deluxe knowledge base: How to set up your Headless Client server
- Gaming Deluxe knowledge base: Arma 3: Headless Client category
- Gaming Deluxe order form, Arma 3 - Headless Client Dedicated Server