ModDoctor

Mod Doctor

Which mod is breaking my game? Mod Doctor answers that, in game, in plain words.

Big modpacks fail in confusing ways: a stack trace that only mentions InventoryGrid.UpdateGui, an error repeated 30,000 times, a patch that silently failed at startup, a friend who joins with an older version of one mod. Mod Doctor watches the game's errors, works out which mod caused each one, explains what it means and what to do, and keeps an eye on your mods and your server.

Versão em português abaixo.

Quick start

1. Install it with your mod manager.
2. Play. If a mod starts causing errors, a notice tells you which one.
3. Press F7 for the full report.

Server owners: install it on the dedicated server too, to compare players' mods with the server's and see every player's problems from the Server tab.

What it does

Diagnose

• Traces every error to a mod, from its stack trace.
• Finds culprits hidden inside game methods. When an error surfaces in a patched vanilla method

(DMD<InventoryGrid::UpdateGui>, no mod in sight), it asks Harmony which mods patched that method. If one of them also failed to load part of itself, it is named as the likely culprit.

• Catches startup failures, including those of mods that loaded before Mod Doctor (recovered from

the start of LogOutput.log).

• Explains each problem: patch failed to apply, incompatible with this game version, error repeating

every frame, error in Valheim's own code, or harmless engine message.

• Flags updates on Thunderstore, highlighting the ones for mods that are causing problems.

Keep the log readable

• After 20 identical copies of an error, repeats are no longer written to LogOutput.log; a one-line

"suppressed N more copies" summary is written every minute instead.

Compare with the server

• When you join, the server compares your installed mods with its own: missing, **different

version, or only yours** (normal for client-side mods such as UI, camera or clock).

• Also warns about a mod installed twice (e.g. a manual copy next to the mod manager's copy).

Measure

• FPS, 1% low FPS, worst frame, memory and garbage collections.
• World objects around you, grouped by type: thousands of one building piece or dropped items are

the usual cause of lag in big bases.

• The slowest mods to load.
• Mod Doctor's own cost, so you do not have to take its lightness on faith. In our testing it stays

around 0.01 ms per frame; performance numbers are only sampled while the window is open.

Server overview (admins)

• Server health (uptime, FPS, memory, objects, players online) and, for every player, their mod

differences and their problems, in game. Also written to BepInEx/ModDoctor/summary.txt.

The window (F7)

| Tab | What it shows | |---|---| | Problems | One card per mod, coloured by severity, with the error, where it happened, the mods involved, what to do and any update available | | Mods | Your mods vs the server's, mods installed twice, slowest mods to load | | Performance | FPS, memory, garbage collections, world objects around you, Mod Doctor's own cost | | Server | Admins on a dedicated server: server health and every player's differences and problems |

The window uses Valheim's own fonts and follows the game's language (English or Portuguese).

Examples

A problem, as written to report.txt:

== TeleportEverything 2.9.1  (OdinPlus-TeleportEverything) ==
  - Incompatible with this game version (443x, ~85/s)
    BadImageFormatException: Expected reference type but got type kind 17
    Where: InventoryGrid.UpdateGui
    Mods patching this method: TeleportEverything 2.9.1, Equipment and Quick Slots 3.1.3
    Pinned on this mod because it is the only one of them that also failed to load part of itself.
    The mod expects game code that no longer exists (built for an older Valheim). Update it; if
    there is no update, remove it.
  - Patch failed to apply (1x)
    ArgumentException: Undefined target method for patch method ... GetTooltip_Patch::Postfix(...)
    Where: TeleportEverything.Plugin.Awake

A player's mods compared with the server's, from the server's summary.txt:

##### Your mods vs the server's #####
== Mepzer (2026-09-29 15:16) ==
   version Stonaar-ValheimBuildCamera: 1.10.0 / server 1.9.0

Files

| File | What | |---|---| | BepInEx/ModDoctor/report.txt | Your own report, rewritten whenever something changes | | BepInEx/ModDoctor/summary.txt | On a server: which mods are failing for which players, and whose mods differ from the server's | | BepInEx/ModDoctor/players/ | On a server: each player's latest problems (.tsv) and mod differences (.mods) |

Configuration (BepInEx/config/bub.moddoctor.cfg)

| Setting | Default | | |---|---|---| | General.Language | Auto | Auto (game language), English or Portuguese | | General.ToggleKey | F7 | Opens and closes the window | | General.ShowToast | true | Notice when a mod starts causing errors or your mods differ from the server's | | Log.SuppressRepeats | true | Stop identical errors flooding LogOutput.log | | Log.SuppressAfter | 20 | Copies written before suppressing | | Updates.CheckThunderstore | true | Look up newer versions on thunderstore.io | | Updates.CacheHours | 12 | How long a lookup is reused | | Server.SendReportsToServer | true | Send your findings and mod list to the server you play on | | Server.CollectClientReports | true | On a server: store players' reports and mod lists | | Server.ServerOnlyMods | ArgusMagnus-ServersideQoL*, Smootheim-*, MidnightMods-NetworkPerformanceSystem | On a server: mod folders players do not need (comma separated, * wildcard), never reported as missing |

The Server tab is shown to players listed in the server's adminlist.txt; the server checks it again before sending anything.

FAQ