I created a free fully featured D&D 5.5e combat simulator

Encounterra’s back! https://encounterra.com

It’s been over two years since the alpha version of Encounterra was released—and then had to be taken down a couple of months later due to infrastructure costs. But now it’s back and better than ever! First, I had to rewrite what I had in C++ for improved performance, and then extend it with many more classes, monsters, and features. Right now, Encounterra can run full combat simulations using all SRD classes and monsters. And by full, I mean with maps, vision geometry, spell geometry…the lot. Basically, it takes no shortcuts and makes no simplifications to the rules or abilities. If an ability is implemented, the combatant can actually use it.

Here’s a list of features:

• Great decision-making—complete legal action sequences are evaluated, including movement and positioning, AoEs, AoOs, and more
• Resource- and action-economy awareness
• A Monte Carlo-first approach—you simulate a statistically significant number of iterations of the same matchup, then choose any iteration to watch as an animated replay
• Full combat logs available for download
• Precise multiattack sequence definitions that are taken into account during action planning
• Effective cooperation between allies—they can buff or heal each other, but only when it’s the optimal thing to do
• Fully implemented abilities, without shortcuts or simplifications (although some design decisions still apply, such as deciding what Charm Person is supposed to accomplish in combat)
• Combatant customization
• Custom combatant creation
• Pre-casts such as Mage Armor and Death Ward
• The option for any combatant to begin hidden or surprised
• A wide range of reactions
• Encounter chaining to model an entire adventuring day, with optional short rests and resource-recovery abilities between encounters
• Day/night and vision mechanics
• Line-of-sight and hiding mechanics—especially relevant for Cunning Action: Hide and Sneak Attack sequences
• A special burrowing layer
• Underwater combat
• Simplified flight mechanics (possibly the only notable simplification)
• Forced movement
• Full implementation of persistent AoE effects
• Concentration mechanics
• Difficult terrain incorporated into action planning
• Optional starting resource depletion
• Full summoning mechanics
• Kobold Fight Club-like encounter generation
• Example encounters
• Swarms that can share a square with other combatants
• No registration required, although registering provides some benefits, such as saving your party to the cloud and keeping a simulation history
• It’s free! Though donations are welcome to offset the infrastructure costs

And more—you might be surprised by some of the things the action planning takes into account.
If it wasn’t clear by now, the smart decision-making is something I’d really like to highlight. IMHO, it’s what makes or breaks a D&D combat simulator. If the combatants can’t make tactically sound decisions, the results aren’t worth much. Similarly, if key spells or abilities are simplified, the value of the simulation suffers again.

That’s why I’ve spent pretty much two years perfecting it and I'm committed to keep improving it and keep adding new features.

Anyway, I hope you enjoy it—and if you do, please share it with your nerdy friends.

I gave it a shot and it's really cool! You know what would be awesome? Being able to import your own classes, species and subclasses, and save them in the local storage. You might need to implement some LUA scripting with an API so that users could implement the more complex stuff though. Really, the only thing that's preventing this to from being an absolute must-have for any DM is that it's SRD only.

Thanks for trying it out!
Yeah, the SRD is a real pain. Especially, because I do have a private build with with ALL subclasses and monsters (PHB + HoF) but I just can't publish it.

There is a custom monster creation feature but it's rather limited at this point. I'm definitely planning on expanding it. I'm not sure how many people would be willing to script their own monsters. I reckon I'd rather wrap all the customization in a user-friendly UI if possible. Scripting or not, there's still the limitation that some abilities are just too exotic to model.

The best case scenario would be entering in some sort of an official partnership with WotC which would enable me to publish non-SRD content.

A partnership wouldn't help for homebrew, though. But if you added an import/export feature, people could share their homebrew stuff to the community like they do on DnDB :)

That's a fair point. I'll make this one of my next points of focus. For the sake of import and export there's no avoiding having to model it with some sort of DEF (data exchange format). Modeling it using json would be my preference. AFAIK, no such standardized thing really exists at this point.

Serendipitously, one guy on enworld messaged me regarding just that. Perhaps I should be the one to standardize it :D

Quote from Thiscord99 >>

Thanks for trying it out!
Yeah, the SRD is a real pain. Especially, because I do have a private build with with ALL subclasses and monsters (PHB + HoF) but I just can't publish it.

There is a custom monster creation feature but it's rather limited at this point. I'm definitely planning on expanding it. I'm not sure how many people would be willing to script their own monsters. I reckon I'd rather wrap all the customization in a user-friendly UI if possible. Scripting or not, there's still the limitation that some abilities are just too exotic to model.

The best case scenario would be entering in some sort of an official partnership with WotC which would enable me to publish non-SRD content.

 Maybe something like ddb’s homebrew creator but also with classes.👍if you can