The game can write every hit, heal, miss, and kill to a plain text file, and a parser turns that file into numbers you can act on. It takes four steps.
/CombatLog 1 before the fight./CombatLog 0 when it ends.The rest of this page covers each step, and then how to read what comes back.
Damage feels different from how it measures. A fight where everything crits feels great, and a fight where you spent ten seconds flying to the next group feels terrible, but neither feeling tells you which of your abilities is pulling its weight. A log records who hit whom with what, for how much, and whether it was a critical hit, a flank, or a miss, so you can compare one run against the next with real numbers.
/CombatLog 1 starts writing to the log file./CombatLog 0 stops writing.Type the first right before the fight you want to study, and the second when it ends. Starting a little early is fine, because the reader works out where the fight begins and ends by itself. Leaving logging on all night is possible, but you will end up with a very large file that mixes together everything you did.
The file lives inside your Star Trek Online install folder, under Star Trek Online\Live\logs\GameClient\. On a typical Windows install that is a path like C:\Program Files (x86)\Star Trek Online_en\Star Trek Online\Live\logs\GameClient, though yours will differ if you installed the game somewhere else or through a different launcher.
One trap: by default the game rotates log files roughly once an hour, so instead of a single file you will often see several named like Combatlog_<date>_<time>.log. The one you want is usually the most recent, but if you played for a while after the fight you recorded, check the timestamps and pick the file written during your run.
To always get a single file, the game accepts a launcher option, -NoAutoRotateLogs, which you add in your launcher's command line or launch options. With that set, everything is written to one file named Combatlog.log. Which screen holds the option depends on how you launch the game, so look for where your launcher lets you add startup arguments.
Open the Combat Log Reader and choose your file. Nothing is sent to a server unless you later choose to create a shareable link or add a run to the leaderboard, because the file is read and analyzed inside your browser.
A log often contains more than one fight. The reader separates fights wherever there is a gap of more than 30 seconds with nothing happening, and if it finds several it asks which one you want. Pick the one you recorded on purpose, and you will land on the results page.
If you do not have a log handy yet, download the sample log and upload it. It is a synthetic 90 second fight made for these guides, not a real player's run, so treat its numbers as an illustration of how the calculations work and not as a benchmark of good performance.
The six cards across the top answer different questions. DPS is your total damage divided by your own active time, from your first hit to your last. In the sample, 8,864,552 total damage divided by about 89.5 active seconds gives 99,045 DPS. Dividing by the whole 91 second fight would give a slightly lower 97,413, which is why the reader uses your active time: joining late or finishing a target early should not drag your number down.
Peak DPS (5s) is your best five second stretch. The sample's peak of 133,257 is about 1.35 times its sustained average, which tells you the fight had real burst windows. When you compare two runs, compare the sustained number first, because peak is the more fragile of the two.
Max Hit names the single biggest hit and the ability that landed it, Crit Rate is the share of your attacks that were critical hits, and Kills counts the killing blows credited to you.
Scroll down and the page splits your damage by ability, which is usually the panel that teaches you the most. In the sample, Heavy Cannons account for 4,189,254 of the 8,864,552 total, which is 47.3%, so nearly half of that build's damage rides on one ability. Beam Array supplies 14.2% of the damage but lands only 9% crits, while every other ability sits between 31% and 39%. That does not prove anything is wrong, since there may be a simple reason, but it is a specific, checkable difference to chase.
The sample's Hit Breakdown reads 139 Critical, 43 Flank, 265 Normal, and 36 Miss, which is 483 attacks in total. The headline Crit Rate is 139 divided by 483, or 28.8%, and the miss rate is 36 divided by 483, or 7.5%. A hit that is both a critical and a flank is counted once, as a critical, so the four categories always add up to your total attacks.
The same page shows healing you gave and damage you took. In the sample you took 755,960 damage across 45 hits and healed 293,000, so healing covered about 38.8% of what came in. When you change something defensive, those are the numbers that should move.
A single log is a snapshot. The value comes from comparing two, and that only works if the fights are alike. Use the same mission and the same difficulty, record the whole run, and change one thing between logs, whether that is a trait, a console, or a bridge officer ability. If you change three things and your DPS moves, you will not know which one did it.
Once recording is a habit, the next step is deciding what to change. Start with Using the Build Planner to Improve Your DPS, and use How to Read Your Combat Log Results as a reference for every stat and chart on the page.