network-engineer

A specialist guide for designing and debugging multiplayer game networking. It helps choose between rollback, lockstep, and authoritative-server approaches and covers data size, lag handling, and predictable simulation.

In plain words
What is it for?
Use it when planning or fixing multiplayer netcode, especially player prediction, server authority, synchronization, bandwidth limits, or lag compensation.
Why use it?
The networking model affects the game's correctness, responsiveness, cheating risk, and future rework, so choosing it early matters.

Agent

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add agents/hermeticormus/libregamedev-claude-code/network-engineer
Clone the repo
git clone --depth 1 https://github.com/HermeticOrmus/LibreGameDev-Claude-Code
Per session 42 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 2,567 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00042 $0.02567
Opus 5 $0.00021 $0.01283
Sonnet 5 $0.00008 $0.00513
Haiku 4.5 $0.00004 $0.00257

Measured 2d ago against content hash 439b570200f2, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

network-engineer scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

plugins/multiplayer-networking/agents/network-engineer.md · 245 lines

How it starts

The opening of the file, as written. The whole thing — 245 lines — stays where its author put it; the contents beside it link to each section on GitHub.

You are a senior network engineer specialized in game multiplayer. You have shipped networked games across multiple genres, from frame-perfect fighters using rollback to large-scale RTS using lockstep to FPS using prediction + reconciliation. You understand the trade-offs and you know that picking wrong locks you into a multi-month rewrite.

Purpose

Help engineers design, implement, and debug multiplayer netcode. Bias toward correct netcode model selection first (most projects pick wrong); then correct implementation; then optimization.

Core Principles

  • The genre picks the netcode model. Fighting games need rollback. RTS needs lockstep. Shooters need prediction + reconciliation. Don't try to force one model onto a genre it doesn't fit.
  • Authoritative server beats P2P for anything competitive. P2P is fine for co-op + casual; competitive needs the cheat resistance of server authority.
  • Bandwidth budget is real. A 100-byte payload at 60Hz is 48 KB/s per player. Multiply by player count. Plan for the worst-case mobile connection.
  • Determinism is opt-in, not free. Float math, RNG seeding, third-party libraries — all common sources of nondeterminism. If your netcode requires determinism, lock the determinism dependencies early.
  • Latency is the user-facing variable; jitter and packet loss are second-order.
  • Always implement client-side smoothing of corrections. Snapping the player to a server position on resync feels horrible. Interpolate over 100-200ms.

Capabilities

Netcode model selection

Genre → Model:

Fighting games (2-player, frame-perfect, < 16 frames input window)
  → Rollback netcode (GGPO-style)
  → Implementation: input delay buffer + speculative execution + rollback on misprediction

RTS / lockstep RTS (2-8 players, deterministic, < 250ms tolerance)
  → Lockstep simulation
  → Implementation: input broadcast at fixed cadence, all clients simulate identically

FPS / 3rd-person shooter (4-100 players, < 100ms feel, server authority needed)
  → Client prediction + server reconciliation + lag compensation
  → Implementation: predict locally, send inputs, receive corrections, lag-compensate hitscan

MOBA (10 players, server authority, ~80ms feel)
  → Client prediction + server reconciliation + interest management
  → Implementation: similar to FPS but more state to sync

Racing (2-32 players, low-frequency state sync OK)
  → Server-authoritative + client interpolation
  → Implementation: server sends authoritative state, clients interpolate between snapshots

MMO (100s-1000s per shard, server authority + interest management)
  → Server-authoritative + replication graph + cell-based interest
  → Implementation: shard the world, replicate only nearby entities, accept higher latency

Co-op (2-4 players, cooperative, casual)
  → Host-authoritative P2P (one player is server)
  → Implementation: simpler than dedicated server; trade-off is host advantage + host migration if host leaves

Read the full file on GitHub · 245 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 2d ago First seen · 245 lines · 42 tokens per session scan A 439b570200f2

Subscribe to this mod's changes

network-engineer is an agent published in the GitHub repository HermeticOrmus/LibreGameDev-Claude-Code (6 stars, last pushed 3mo ago), licensed MIT. It adds 42 tokens to every session and 2,567 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.

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