Project Zomboid Co-op Guide (Build 42.19): Host, Join, Meet Up

Build 42.19 · Host / Multiplayer · ports 16261 / 16262 · map friend visibility (4 levels)

Quick-start: team up in a few minutes

1. Same branch and revision. Everyone must be on the same Steam branch (Build 42 Unstable for this guide) and the same patch after updates. Mixing B41 and B42 fails.
2. Match mods. Workshop items, Mod IDs, maps, and load order must match host and clients. Test vanilla first when a join fails.
3. Host: Main menu → HOST → create or select settings (name, password, sandbox, player limit) → Start. When loaded, use ESC → Invite Friends, or let friends use Steam “Join Game”.
4. Join: Main menu → MULTIPLAYER → favorites, browser, or IP + port. Prefer private or whitelisted hosts during the MP test period.
5. Meet up: Pick the same spawn town, turn on friend map icons (see map visibility below), or use admin teleport once. Claim a safehouse later for shared respawn when the server allows it.
6. Back up before updates. Unstable patches are expected to disrupt multiplayer worlds.

Host, join, or dedicated server

Host steps (friend group)

1. From the main menu, open HOST.
2. Create or edit server settings: public name, optional password, max players, sandbox preset or custom options, and mods if any.
3. Set ports deliberately if you are not using defaults (see below). Leave UPnP on unless you already forward ports manually.
4. Start the server, create or load a character, then invite friends (ESC → Invite Friends) or have them join via Steam.
5. For a closed group on the MP test build, prefer whitelist / non-open accounts once the session is stable. See the whitelist guide.

Ports: 16261 and 16262 (not 8766)

Current server options use two UDP-related settings. Older co-op articles that list 16261 + 8766 are out of date for this build.

DefaultPort=16261
UDPPort=16262
UPnP=true

• Forward (or UPnP) the ports your live server INI actually lists—not an invented per-player range, and not legacy 8766 from old guides.
• UPnP=true tries to open ports on a UPnP gateway; if that fails, the server falls back to its configured defaults. Check the server log instead of only restarting.
• Direct IP joins need a reachable host and the correct DefaultPort. Steam Relay can help some NAT cases but does not fix wrong ports or version/mod mismatch.

Deeper admin notes: server administrator tips and Getting Server Info stuck.

Co-op-friendly server options

Exact Host UI labels can move between tabs; the option names below are the ones you set for Host or a dedicated server.

Map friend visibility (four levels)

In-game map visibility levels for remote players on 42.19:

For private co-op, 2 or 3 is usually enough. Set the option in Host → Manage Settings (Players / related group) or in the server INI, then restart if the running server does not hot-apply the change.

Finding each other after spawn

Players still land at different buildings inside a chosen region. Use these tools instead of treating random spawn as a bug.

Safehouse respawn (after you meet)

1. Confirm server options allow player safehouses and safehouse respawn.
2. Claim a suitable building as a safehouse; invite friends via the safehouse UI.
3. Each member enables respawn in that safehouse when the option is available.
4. Deaths then return members to the house instead of a random world spawn (subject to current rules and membership).

Build 41 vs Build 42 for co-op

Full branch comparison: Build 41 vs 42 multiplayer. Status of the MP test framing: B42 multiplayer is live as a test build.

Remote Play and streaming (optional only)

Steam Remote Play Together or third-party game streaming can still share a local split-screen session over the network. That is a video/input stream of one machine—not the same as native Host/Join multiplayer.

• Use when: you specifically want couch-style split-screen with one PC, or you are experimenting offline.
• Do not use as: a substitute claim that “Build 42 has no multiplayer.” On 42.19, online multiplayer exists on the Unstable client.
• Trade-offs: shared view, host hardware load, possible UI limits for player 2, and network quality dependency.

Playing together without ending the run early

Join failures: check these first

• Version mismatch: same Steam branch and post-update restart for host and clients.
• Mod mismatch: align Workshop IDs and enable lists; try a clean no-mod host.
• Ports / firewall: DefaultPort / UDPPort, UPnP log lines, OS firewall allow rules.
• Password / whitelist: server password vs account credentials; closed servers need pre-created users.
• Logs over rumor codes: read client and server console text instead of unofficial numeric “code” lists — multiplayer log triage.

Practical limits

• Build 42 multiplayer is an MP test build—not finished, desync-free, or equal to a future stable release.
• The next Unstable patch may not keep today’s world intact—back up before updating.
• Vehicle/zombie sync quality and PVP balance can change between patches.
• Remote Play is optional for split-screen streaming, not the primary online co-op path on 42.19.

Summary

1. On 42.19, use HOST or MULTIPLAYER—official online co-op is available as an MP test build.
2. Match branch, revision, and mods before blaming ports.
3. Default ports are 16261 and 16262—not the old 16261/8766 pair.
4. Map icons use four visibility levels; Everyone is 4.
5. Tune PVP, sleep, pause-when-empty, and safehouses for friend groups; back up before every update.
6. Keep Build 41 for long stable servers; use B42 when the group wants current systems and accepts resets.