Hermod

Hermod

Performance and networking for Valheim dedicated servers. It changes no gameplay.

Hermod cuts the server's outgoing traffic by about two thirds, opens up two limits the game

leaves fixed, and keeps a record of where the server's time actually goes so a slowdown can be

diagnosed rather than guessed at.

What It Does

Compresses network traffic. On a real server 8.6 MB of outgoing traffic became 3.0 MB, with

no change to frame time or CPU. Every player needs the mod for this part; a player without it

just exchanges ordinary packets.

Raises the limit on world data per player. The game stops sending a player world updates once

a fixed amount is in flight to them, which bites hardest on players furthest from the server.

That limit is adjustable.

Limits time spent building new terrain. Generating a zone with a crypt or a village in it is

the single most expensive thing a server does, and several can land in the same tick when people

explore in different directions. The budget spreads them out.

Improves the Steam connection settings. The game pins its send rate to a fixed value and

never disables Nagle batching. Hermod raises the ceiling and turns the batching off, and only

ever in the direction that helps.

Records what the server is doing. One row a minute to a spreadsheet: frame times, memory,

object counts, per-player bandwidth and update rate, compression, terrain generation and saves.

Most of it needs no hooks into the game, so it keeps working after a Valheim update.

Watches for stale player records. When the server still thinks one player can see another

who has gone out of range, it says so and counts it. This is bookkeeping rather than anything

on screen, because each client drops the object on its own. It only watches; nothing about

portals or players behaves differently.

Does not cap the frame rate. A Valheim server sends updates to one player per frame, so

capping the frame rate makes things worse for everyone. Hermod leaves it alone and refuses a cap

that would slow updates below ten a second.

Installing

Install it on the server. Install it on players too if you want compression, which is the one

part that needs both ends.

The commands need it on the client you type them from, because a Valheim dedicated server has no

console of its own. Commands travel to the server and are checked for admin rights first.

A crossplay server gets the measurement but not the networking. Compression and the Steam

settings both need a Steam connection, which a crossplay server never makes. Hermod says which

kind of connection it opened in the log at startup.

What It Writes

Three files in BepInEx/config, and a short summary to the log every few minutes.

| File | Contents |

|---|---|

| gbv.valheim.hermod.session.csv | One row a minute: frame times, CPU, memory, object counts, send rates, compression, terrain generation, saves |

| gbv.valheim.hermod.peers.csv | One row a minute per player: ping, link quality, bandwidth, queue depth, update rate |

| gbv.valheim.hermod.report.json | The session, with the worst frames and slowest zones timestamped |

Four columns answer most questions: ms_p99 is what a bad frame looks like, frames_gt100 is

how often the server actually hitched, gc_stall_ms is how much of the minute went to garbage

collection, and slow_unexplained is slow frames Hermod cannot account for at all.

Percentile columns are bucket edges, so ms_p99 = 16.7 means 99% of frames were at or below

16.7 ms. The _max columns are exact.

Every column is explained in wiki/Reading-The-Session-Log.md.

Commands

Typed from an admin's client.

| Command | What it does |

|---|---|

| hermod_status | Frame time, CPU, object counts, compression and send rate right now |

| hermod_peers | Per player: ping, queue depth, how often they are updated |

| hermod_mark | Stamp a labelled boundary into the logs, for comparing before and after |

| hermod_profile | Flip the whole set of settings at once, live |

| hermod_compress | Packet compressi