LagFinder

Your server is lagging and spark tells you "block entity ticking: 34%". Great - but where? Which chunk, which farm, whose base?

LagFinder answers that in one minute, with no client mod:

/lagfinder start 30    - sample 30 seconds (zero overhead when idle)
/lagfinder top         - the hottest chunks, ranked

#1 overworld chunk [5, 5]   4.04 ms/tick (42%)  [BE 1.13  ent 2.91]  zombie 2.42, hopper 1.13  near Steve (12 m)  [tp]
#2 overworld chunk [60, 60] 0.48 ms/tick (5%)   [BE 0.48]            hopper 0.48                                  [tp]

/lagfinder show        - glowing red/orange/yellow markers over the hottest chunks, visible to every player, even vanilla clients
/lagfinder hide        - remove the markers
/lagfinder export      - self-contained HTML heatmap + table you can open in a browser or send to your players
/lagfinder status      - is sampling running, how many ticks were measured

(/lagmap works as an alias for every command.)

What it measures, per chunk

• block entities (hoppers, furnaces, modded machines) - with the type that costs most
• entities - with the mob type that costs most
• scheduled block & fluid ticks and random ticks
• what share of the whole server tick that chunk takes, and the nearest player
• click [tp] in chat to teleport straight to the chunk

Why LagFinder

• Real measurement, not an estimate. Every block entity, entity, block tick and random tick is timed with nanosecond precision and attributed to its chunk.
• Server-side only. Nothing to install for players. Works with vanilla clients.
• No dependencies. No Fabric API, no Architectury, no Kotlin.
• Zero overhead when not sampling - one boolean check per hook. Start it only when you need it.
• Spiritual successor to LagGoggles (1.12) and Observable (up to 1.21.4), rebuilt from scratch for 1.21.8 - 26.3.

Versions

Fabric (Quilt works too) and NeoForge: 1.21.8, 1.21.9, 1.21.10, 1.21.11, 26.1.x, 26.2, 26.3. Java 21 for 1.21.x, Java 25 for 26.x. Pick the file that matches your game version and loader.

Permission level 2 (op) is required for /lagfinder.

How to read the result

ms/tick is how much of every server tick that chunk costs. A vanilla tick has 50 ms; a chunk that takes 10+ ms/tick on its own is the reason your TPS drops. The breakdown tells you what in that chunk is expensive (a mob farm, a wall of hoppers, a modded machine), and the nearest player tells you whose it is.

Found a bug or want a feature? Use the Issues tab.