Preface

I have been running Advanced Dungeons & Dragons (AD&D) in one form or another since the late 1970s. The Advanced Dungeons & Dragons 1st Edition Dungeon Master’s Guide (DMG) has sat on my shelf for most of that time — dog-eared, annotated, occasionally argued with. It is a remarkable document: dense, idiosyncratic, and in places so thoroughly the product of one man’s thinking that it resists easy summary. Gary Gygax wrote it as though he expected you to read it twice, which is probably the right expectation.

What you are reading now is not a replacement for that book. It could not be, and it would be wrong to try. The DMG is the DMG. What this website does is sit alongside it — the Advanced Dungeons & Dragons 1st Edition Dungeon Master’s Guide Overlay (DMGO) tells you, section by section, where Oath-Bound departs from the DMG and why, and where it does not. The Oath-Bound Rules Module (CRM) records what replaced what was changed. Together they give you the full picture.

Most of it does not depart. AD&D 1st Edition, as published by TSR, Inc. in 1979, is a coherent and well-considered system — and crucially, a sparse one. That sparseness is not a weakness. It is the property that makes it an ideal foundation for a customised rule system. The rules describe what happens without over-specifying why, which leaves room for a world to have its own reasons. New mechanics can be introduced, old ones replaced, and the fabric of the game survives largely intact because there is not much fabric to disturb.

Later editions of the game moved in the opposite direction. They accumulated subsystems, feat trees, codified interactions, and explicit rulings on situations the original left to judgment. Fourth Edition — the Player’s Handbook published by Wizards of the Coast in 2008 — is the sharpest example: paragon paths, epic destinies, powers for martial classes, a combat system that rewards careful reading of interlocking mechanics. It is a different kind of game, designed around different assumptions, and it is not without its virtues. The tight systemization that characterizes it was not an accident or a failure of taste — there was a genuine and reasonable hope that a sufficiently rigorous rules architecture might allow technology to generate compelling game materials: modules, encounters, campaigns, delivered at scale. I held that hope myself, once. What I failed to understand then was that the creation itself — the world-building, the improvisation, the negotiation between Game Master (GM) and players over what the fiction means — was not an obstacle to be engineered around. It was the point. A system optimised for delivery of pre-generated content is optimised for the wrong thing. But the violence required to introduce Oath-Bound-scale changes to that system would be substantial. The elaboration is load-bearing in a way that AD&D’s sparseness is not. In Oath-Bound, by contrast, the departures from the original are in most cases minimal — targeted, not wholesale.

The parts that have been changed were changed because play in Oath-Bound demanded it — not because change was an improvement in principle, but because specific consequences at the table made specific rules untenable or uninteresting. Every deviation here has a history behind it.

One mechanical decision made early — in the early 1980s — has implications throughout the system and is worth flagging here. At that time, many GMs were moving toward percentile dice as their primary resolution mechanism, and I was among them. The appeal was granularity: a d100 system allows finer distinctions than a d20, supports truly minor magic items that confer small percentage benefits, and produces a resolution model that feels proportionate to the differences between characters. TSR eventually moved in a similar direction themselves, which suggests the instinct was reasonable if not original. I claim no innovation in adopting it.

The consequences are widespread. Combat, skill resolution, and most mechanical adjudication in Oath-Bound uses d100. That said, d100 was adopted where it adds value, not as a blanket replacement. Where a d20 provides perfectly adequate resolution — and there are areas where it does — it was left alone. The appendix random generators are the most visible example: converting them to d100 would add complexity without adding anything useful, so they were not converted.

A GM who dislikes percentile resolution is not locked out of Oath-Bound. The world, the fiction, the economic model, the theological structure — none of that depends on how you roll dice. The d100 elements can be replaced with d20 equivalents with minor accommodations, and the rest of the system remains intact.

Where d20 was kept, the reason is the same: it was already doing the job. Adequate resolution at lower complexity is not a compromise. It is the correct engineering decision.

Alignment is gone, replaced by something that fits a world where the gods are real, present, and have opinions. Hit points work differently, or rather they are understood differently — the abstraction is preserved but the fiction around it is tighter. These are not tweaks. They are decisions, and they have consequences that ramify through the rest of the system.

They are also, frankly, opinionated choices. The Oath-Bound rules are not objectively better than the DMG rules they replace. They reflect a particular preference for a certain kind of play — one that leans on fiction and judgment ahead of mechanical resolution. Roles before rolls, as the shorthand has it. That preference has practical consequences: the weapon-versus-armour class adjustment tables, which reward close attention to equipment interaction, are not the kind of detail this system wants to emphasise. The weapon model has been flattened to fewer, more generalised types. The table complexity has been reduced. A player who loves that granularity will find it is gone, and I will not pretend the loss is neutral. It is a choice, made by someone who finds that kind of bookkeeping gets in the way of the game he wants to run. Another GM, equally reasonable, might make the opposite choice. The original rules are still there for them.

Two other changes are significant enough to flag here, because the reader will encounter them early and they colour everything that follows.

The first is clerical magic. The oath economy that underlies Oath-Bound — the system of binding promises, divine sanction, and institutional authority that holds the world together — raises an immediate question: if oaths have real weight, something must enforce them. Gods do not descend personally each time a vow is broken. The clerical miracle system is the answer to that question. Clerical power in Oath-Bound is not a daily transaction between a priest and an attentive deity — it is the operational expression of a standing relationship between an institution and a god, with the cleric as the instrument through which that relationship acts in the world. The DMG’s prayer-and-memorisation model describes a mechanism without a world to support it. The Oath-Bound replacement has both.

The second is arcane magic. Most fantasy treatments of magic are deliberately vague about mechanism — the vagueness is part of the aesthetic. But a spell cast from a book still requires energy to instantiate its effect. That energy has to come from somewhere. An engineer asked to model a magical system would start there, and that is where Oath-Bound starts. The answer is nwyf — the orthogonal counterpart to wyrd, the substrate through which arcane effects are instantiated. Nwyf is not physics. The characters who use it do not think of it in those terms, and most could not explain it if asked. But it gives the system an internal consistency that purely traditional treatments lack. Where the effect comes from, what it costs, and why some casters can do things others cannot all have answers that follow from first principles rather than convention.

One area deserves a specific note. The AD&D experience and level advancement model has well-documented problems — it rewards the wrong behaviors, delivers advancement in discontinuous jumps, and imposes costs that actively work against the kind of play it claims to encourage. The root problem is that the XP formula was never doing what it claimed to do. Every table mutated it. Every GM overrode it. The formula provided the appearance of objectivity while GM judgment did the actual work. Oath-Bound simply acknowledges this.

XP in Oath-Bound is awarded solely by the GM at the Session Journal — the fixed ceremony conducted at the end of every session — honestly, transparently, and collaboratively. It is not accumulated by formula and is not tied to kills, treasure, or any other prescribed activity. The vanilla AD&D level structure remains intact underneath. A character does not level up — they arrive at a point where they are functioning at a new level. The level is a recognition of what the fiction already established, not an event.

This is a targeted intervention, not a reconstruction. The parts of the original model that work are still working. What has changed is the honest admission that the GM’s judgment was always the instrument. The DMGO gives that judgment better tools: the Session Journal, the Competency Profile, and the collaborative discussion that produces a defensible, witnessed award. That is the approach taken throughout the DMGO, and it is worth saying so plainly.

Where a section of the DMG stands as written, the DMGO says so and moves on. Where something has changed, it explains what changed and points to the CRM rules that replace or extend it. Where a rule is left to the GM’s discretion, that is noted too — because the honest answer to some questions is that the table gets to decide.

The marker system used throughout the DMGO is explained in the Legend. Read that first.

— Mogadon, May 2026