Bug Tracking for RTS Games

Real-time strategy is one of the most demanding genres to build and to debug. You have hundreds of units running AI and pathfinding every tick, selection and order handling that must feel frictionless, and, for multiplayer, a lockstep simulation that requires every machine to compute byte-identical results forever. A single divergent calculation does not cause a small visual glitch; it causes a desync that splits the game into two incompatible realities. The bugs are subtle, timing-dependent, and brutal to reproduce. The way through is determinism and a command-and-checksum log that lets you replay any match and find the exact tick where things went wrong.

Lockstep determinism is non-negotiable

Most RTS multiplayer uses lockstep: instead of sending unit positions, each client sends only the player's commands and every client runs the identical simulation to compute the same result. This keeps bandwidth tiny even with huge armies, but it imposes a merciless requirement, that the simulation be perfectly deterministic across machines. Any difference, a float that rounds differently on another CPU, an iteration over an unordered collection, an unseeded random call, causes the clients to diverge. Once they diverge the game desyncs, and players see their units doing different things on each screen.

Because the simulation is driven entirely by the command stream, that stream plus the starting state is a complete, replayable description of any match. If you log every command with the tick it was issued on, you can replay the whole game deterministically and reproduce any bug, single-player or multiplayer, exactly. This is the foundational investment an RTS codebase has to make. Without lockstep determinism you cannot have trustworthy multiplayer or trustworthy replays, and you cannot reproduce the timing-dependent bugs that otherwise haunt the genre forever.

Catching desyncs with per-tick checksums

A desync is only easy to fix if you catch it the instant it happens, and the tool for that is a per-tick state checksum. Each client hashes its simulation state every tick, unit positions, health, resource totals, and the like, and exchanges or logs the hashes. The first tick on which two clients disagree is the precise moment the divergence began, which narrows a vague the game desynced report down to a single tick and a single mismatched value. Without checksums you discover the desync minutes after the cause, with no way to walk back to it.

Make the checksum granular enough to localize the culprit. Hashing per subsystem, so you know it was the pathfinding state and not the economy that first diverged, saves enormous debugging time. When a desync report comes in with the diverging tick and subsystem, you replay both command streams to that tick and compare the state to find the one calculation that differs. This is how desyncs go from career-ending mysteries to ordinary, if delicate, bugs. The checksum is the smoke detector; the command log is the recording that tells you what started the fire.

Pathfinding and unit AI at scale

Pathfinding is the RTS bug factory. Hundreds of units sharing a navmesh produce emergent jams: units that clump at a chokepoint, oscillate between two routes, push each other off cliffs, or freeze because local avoidance deadlocked against a wall. Unit AI compounds it, a unit that picks a target, walks toward it, gets shoved, recalculates, and loops, looks broken and tanks performance. These bugs depend on the exact positions and orders of many units at once, so they are nearly impossible to reproduce from a description and trivially reproducible from a deterministic replay.

This is where the command-log replay earns its keep. Because you can replay the match to the exact tick where the units jammed, you can attach a debugger, visualize the navmesh and the units' computed paths, and watch the deadlock form. Log each unit's path, movement state, and current order so a captured replay carries the context to localize the jam fast. Pathfinding fixes are risky because they ripple across every unit, so being able to replay the precise failing situation before and after a change is what keeps you from trading one jam for three new ones.

Selection, commands, and input feel

The other half of an RTS is the command layer the player touches: box-selecting units, issuing move and attack orders, queuing commands, and using control groups. Bugs here are about responsiveness and correctness of intent. A selection that drops a unit, an attack-move that some units ignore, a control group that loses members after they die and respawn, all break the player's sense of control even though the simulation underneath is fine. Because these bugs are about the mapping from input to command, capturing the raw input and the command it produced is what makes them reproducible.

Log the selection set and the issued order for the actions a player reports as wrong. When they say half my army ignored the attack order, the log might show the order only applied to the units selected at issue time and that two were mid-respawn and missing from the set, which is a precise, fixable selection bug. Input feel also has a latency dimension: in lockstep there is an intentional command delay, and tuning it badly makes the game feel sluggish or, if too short, causes commands to miss their tick. Tracking the command-to-execution delay keeps that responsiveness honest.

Setting it up with Bugnet

Bugnet's in-game report button fits the RTS model neatly because the command log and tick state are exactly what you want to attach. Push the recent command stream, the current tick, and the per-subsystem checksums into custom fields, and route the match seed and player setup through player attributes. A desync or pathing report then arrives with the diverging tick, the subsystem that mismatched, and the commands needed to replay the match, so you reproduce the exact failure in a debug build instead of begging the player for steps that lockstep timing makes impossible to give.

Desyncs and pathing jams cluster around specific maps, unit interactions, or build versions, so Bugnet's occurrence grouping folds duplicate reports with the same diverging subsystem or stack into one issue with a count. That ranks which determinism bug is breaking the most matches. Crashes are captured with stack traces and platform context automatically, which matters because cross-platform float behavior is a classic desync source, and seeing which platforms a desync spans is half the diagnosis. Filtering by map, by tick range, or by build version turns a pile of the game desynced reports into targeted, replayable investigations in one dashboard.

A replay-driven testing culture

The RTS teams that stay sane build their entire test culture on replays. Every reproduced bug becomes a saved command log that an automated harness replays headless and checks for crashes, desyncs against a recorded checksum trail, and pathfinding regressions like units failing to reach a destination. Because the simulation is deterministic, these replays are perfectly reliable, so a green run genuinely means the bug is gone and a checksum that matches across a CI matrix of platforms genuinely means determinism holds. Replays are the load-bearing wall of RTS quality assurance.

Push determinism discipline into everyday coding too. Forbid unordered iteration in simulation code, route every random call through the seeded simulation stream, and use fixed-point or carefully controlled float math where cross-platform consistency matters. Every desync you fix should leave behind a checksum replay that guards that path forever. The genre's difficulty is real, but it is tameable: with a deterministic simulation, a command log, and per-tick checksums, the scariest bugs in strategy gaming become reproducible, localizable, and regression-proof, which is the only sustainable way to ship a multiplayer RTS.

RTS bugs are timing and determinism bugs. Log the command stream and a per-tick checksum, and any desync or pathing jam becomes a replay you can step through.