Observable is a performance monitoring mod used to determine lag. It is similar, but not the same as spark. Observable lets you see the length of each tick that is affected by each entity. Such as a mob which makes ticks take longer will have a higher number than one that was more minor. The score is usually scored with µ seconds (milliseconds).

To get started you need to open up the special panel to get the information. The default key bind is the letter R, but you can change this if it conflicts with an existing keybind. The panel opens up and provides an interface that is simple but requires some getting used to. You are going to want to press Profile TPS to get information about TPS, when the TPS is profiling (and after also) the entities will have the number of milliseconds a tick above them. You can also adjust the settings with the settings button. After the 30 or so seconds of monitoring are over you will get a link in the chat which will give you a detailed analysis of what is going on. If you want you can view this in-game by copying the link or hash into the bar in the panel and get an in-game analysis, if not you can just view it from a web browser. The links can be freely shared with anyone for debugging purposes. There are many more debugging tools in the mod.

The results page has individual results, chunk results, Aggregate results, info, and other metrics. You can see information about each dimension and the chunks and the entities, the time, the position, and the command to teleport to them. You can also download the report as an offline file for offline viewing or sharing long-term storage. The mod works with many other mods and works with most Fabric packs as well as Forge Packs, though MC Forge packs are less tested.

This mod is in many ways not a replacement for spark, spark displays the info about general Java classes which are causing slowdown while this mod does mostly for which entities. Both are good for testing modpacks and servers and other information. Both mods need to be installed on the server to work correctly. Both of them have pretty good interfaces, though I would say observable’s is a little better.

This mod requires Fabric Language Kotlin installed, if you do not have it installed the game will most likely crash due to the Kotlin-specific classes not being found.

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Observable Mod