Getting Started As a System Designer

Creating a new system from scratch can be a difficult process, but Tabletop Mirror provides support for you and your system for every step along the way.

Note: for light homebrew, we highly recommend checking out Modules. They make homebrewing an existing system seamless. Otherwise, read on!

But remember, this is just a starting guide. It's going to go over a lot of the major topics, but the details will be left to explore in other guides (which we'll link to at the bottom)!

Templates

If your system is similar to or based on any of the Tabletop Mirror official systems, you can start by using one of these systems as a template.

However, if you want to start from scratch, you can just create a brand new rule system from the Rule Systems page, by clicking the top right create button, and giving your system a name. Then, go ahead and skip to the next section!

To use a template, Tabletop Mirror currently officially supports and provides the following rule systems as templates:

• Dungeons & Dragons 5th Edition
• Pathfinder 2nd Edition

You can also use any system that you can edit as a template.

When you've decided on a system to use as a template, click the copy button to make a duplicate of the rule system for you to build your own system from.

Setting Up The Basics

Once you have started your system (with or without templates), you will see several tabs for editing your Rule System — each controlling a specific sub-set of how your system works.

To have full VTT and homebrewing support for your system, you will need to eventually complete all these tabs. But don't worry, you can always edit your rule system in the future with minimal friction.

On the "General Tab", you'll see options for "Description", "Default Dice", and "Bonus Options".

The description of your Rule System will be used to represent your system across TTM — to new and old users alike.

Default Dice

Meanwhile, the Default Dice of your system is used to designate the "default" kind of roll that is used in your system. For example:

• D&D systems use a "1d20" default dice
• Pathfinder systems also use a "1d20" default dice
• GURPS systems will use "3d6" as their default dice
• Step-Die systems may not have a default dice, but their rule system will still have one. They can simply set their default dice to their lowest dice step, or some other logical value.

Specifically, by setting a default dice, new checks in your system will automatically use this dice set-up, including any "advantage"/"disadvantage", "exploding", and other modifiers. Of course, after being created, a check can be overridden to use some other kind of dice roll.

In other words, setting your default dice is strictly for your convenience and not required to be set.

Bonus Options

When users, including yourself, are creating bonuses in your system as a part of creating spells, items, or other entities, they have a few options for bonus creation:

Specifically, you will notice that bonuses consist of the bonus value (not configured in the example above), the bonus sub-group (which allows users to set-up sets of bonuses that are applied together, without applying all bonuses), and the bonus type. However, regardless of how the bonus is configured, it will follow the settings of the Rule System that the entity belongs to.

There are two main settings available to customize how bonus calculations are made in your system: identical bonus stacking and rounding strategy.

If you allow identical bonus stacking, then regardless of the type of a bonus, it will stack with all other kinds of bonuses. If you disable it, identical bonuses will not stack with one another and only the first applied bonus of a particular type will be applied (based on the bonus' precedence — 1st precedence bonuses will override 2nd precedence, etc.).

In addition to the ability to disable rounding of bonus values altogether, you can set your system to follow 2 kinds of rounding:

• Down: Decimal values of bonuses are always rounded down (5.5 becomes 5, 5.9 becomes 5).
• Round: Decimal values are rounded (5.5 rounds up to 6, 5.4 rounds down to 5).

In addition, there are two variants of each of these rounding strategies:

• Default: Rounding of decimal values only happen when all bonuses have been applied.
• Strict: Rounding of decimal values happen for every bonus before they are applied to a character.

For example, if you have a simple Level 3 character with 10 Strength and 2 (stacking) bonuses that add half your level to your Strength each, you will get a different final value depending on how your bonus strategy is configured:

As you can see, with strict rounding, each of the bonuses that grant half your level to Strength is rounded up to a bonus of +2, whereas it remains as +1.5 with non-strict rounding. Thus, the final value granted by these two bonuses is +4 in the strict case, while it is only +3 with non-strict rounding.

Entity Set-Up

Once you have set-up these basic settings, you will next want to set-up the various types of "Entities".

On TTM, the term "Entity" refers to the various types of content you can create on TTM. The exact meaning and best usage of these Entities will be covered in a future guide. For now, consult this quick overview of the various Entity Types on TTM:

When building a Rule System, you generally want to start with the customization of "The Core Entities":

• Abilities
• Feats
• Heritages
• Items
• Spells

And while these terms are typically associated with D&D and other d20 systems, TTM provides tools for you to rename these functionalities.

Customizing these Entities mostly consists of a few key steps common to all of these entity types:

1. Decide what kind of content will be represented with your entity type
2. Set up Entity Fields
3. (Optional) Set up the Label Override
4. (Optional) Set up the look and feel of your system with Previews and Overviews

Deciding How To Set Up Your System

The first step to setting up your system in TTM is determining what each TTM Entity will represent. For large strokes of your content, you will likely want to use one of the core entities mentioned above. Note: depending on your system, you may not need to set-up or use all of the entity types provided.

Abilities are generally re-usable sets of powers, actions, or bonuses. Specifically, Abilities can be added to other abilities, items, classes, feats, heritages, or characters themselves. Thus, you can use these to represent the basic building block of your system. In a way, they are "What can a character do?"

Feats are similar to abilities with the notable exception that they are designed to be driven primarily by character progression. For example, they might be abilities that players pick every odd level (Pathfinder) or granted at some other regular interval — perhaps with prerequisites for players to chose them.

Heritages are collections of abilities that are altogether given to characters at their creation. They may define backgrounds (D&D 5E), ancestries (Pathfinder 2E), or other backstory abilities characters that may be chosen.

Items are entities that are not part of a character build itself, but rather an equip-able entity that is gained on a per-campaign basis. Thus, the same character may have different items in different campaigns — even if all else is the same.

Spells are potentially magical abilities that are available to a wide-swath of characters, but all draw from the same pool of resources. For example, spells might all require "Mana" to be cast, consume "Stamina" when used, or even something like "Tech Points" to activate. The needs and capabilities of Spells will likely vary significantly between systems.

In the future, we will create guides specifically describing how to reframe this structure for other, less-D20 oriented systems.

Note: Item Properties, Casting Modifications, Campaigns, Classes, and Characters also all provide Entity Field Support, but we do not cover them in this guide.

Set Up Entity Fields

Once you have decided what each entity type will represent, you must set-up Entity Fields. Doing so, will also likely better familiarize yourself with how to represent your system best in TTM.

In short, for every kind of value, stat, or other measure of your system, it will be represented either as an Entity Field or a Derivation (more on this later).

What Kind of Entity Field Should I Use?

The best way to decide what kind of Entity should represent each such stat is to ask yourself, "At what point does this stat change between Entities?"

For example, every item might have its own "Durability" stat. Thus, "Durability" should be an Item Entity Field, or "Item Field" for short. Meanwhile, every Spell may have a tag for "Primary Use", thus "Primary Use" becomes a "Spell Field".

In some cases, there might be multiple ways to represent information in your system. You will have to experiment with each approach to decide what works best for you.

Ultimately, wherever you set up Entity Fields, you will find those values automatically being compatible with and available in character computations.

Types of Entity Fields

When you create an Entity Field, you will find there are 3 types of fields: Numerical, Alphanumeric, or True/False.

Numerical Fields represent numbers. They can be simple unchanging numbers or a calculation themselves.

Alphanumeric Fields represent free-form text values, like the description of an area of effect, the classification of abilities, or other open-ended values. You can also restrict these values to a list of possible options, rather than full free-form.

True/False Fields represent values that are either True or False — or in other words, are yes or no values.

Entity Fields generally have a lot of configuration options that will be covered in another guide, but this information provides the basics of creating Entity Fields.

Note: New Entity Fields will automatically be added to all entities of that type in your Rule System. If an Entity is ever found missing an Entity Field, its creator will also see an option to re-sync their Entity with the Rule System's configuration. To create Entity Fields that vary between campaigns (for example, in the case of expansion modules for your system), consider using Modules.

Set Up Label Overrides

Once you have decided what each entity type will represent and set-up Entity Fields, you can optionally use the "Labeling Override" setting to rename it to something that better suits your system's needs.

When you do so, you'll notice all of TTM's navigation and menu systems rename themselves to match your new label. For example, the "God Complex" Rule System has renamed many of the core entity types in the navigation menu:

Specifically, "Abilities" have been renamed to "Actions/Feature", "Classes" have been renamed to "Powerset", "Feats" have been renamed to "Boons/Bane", and so on.

Set Up Overviews

Additionally, to further customize the look and feel of your system, you can replace the default informational view for entities:

With a more personalized Overview:

To do so, simply provide the general structure you want your entity overviews take in your Rule System Settings. For example, the above Spell Preview was configured as such:

It may seem daunting at first, but really this is just another markdown field with an additional feature: value placeholders.

When you are creating your Overview layout, simply use standard markdown to describe the constant parts of your layout. For example, the words "Spell Category", "Spell School", etc are all bolded at the start of their respective lines.

Then, when you'd like to insert a placeholder for TTM to insert a specific piece of information, simply type "{" to see a dialog for you to select the kind of value to be inserted at your location:

Once you have completed your Overview, save your Rule System to see your newly rendered Overviews used for all entities of that specific type.

Character Derivations

In addition to the various types of provided Entity Fields above, there is also a specific type of specialized Entity Fields known as "Character Derivations".

These Character Derivations are very similar to Entity Fields in many ways, but are specifically tailored for outlining the various Character stats of your system.

For any and all numerical stats, metrics, or values specific to Characters, you should generally be using Character Derivations over Character Entity Fields.

Specifically, Character Derivations vary from Entity Fields in a few key ways:

• Character Derivations are always numerical.
• Character Derivations support player input (for example, skill point allocation).
• Character Derivations, themselves, have a type of Entity Field known as "Properties", that are specific to each Derivation.

Beyond the above differences, Character Derivations are also grouped into Derivation Groups. The main purpose of these Groups is to signal to TTM that the derivations within each group share some sort of category, or mechanically share investable resources.

For example, by setting up a Group known as "Skills", you can create a Derivation for each of the various Skills of your system and allow them to share a pool of allottable resources (i.e. "Skill Points").

Closing Notes

There's ultimately a lot of features available to System Designers and this guide is meant to serve as a starting point for your own creations.

From the information above, you should be able to begin building your new Rule System, as well as the entities it contains. For more information on this process, consider the Getting Started As a Homebrewer or Gamemaster guide. Or if you'd like a practical example, check out our guide for setting up D&D 5E from scratch, which walks you through the entire process of building the 5th Edition of Dungeons & Dragons.

In the future, we'll be creating more detailed guides about each of the principles discussed above, as well as how your Rule System configuration choices will carry over into the Homebrewing and Playing Experience of your community on Tabletop Mirror.