OSINT-6 CHANGELOG 251021

The first major rules decision for the OSINT-6 Core Rulebook was whether to build a new engine or adapt an established one. We chose the System Reference Document 5.2.1 as the foundation because it offered a familiar resolution language, a complete body of usable procedures, and clear publication under the Creative Commons Attribution 4.0 International License.

That choice established the basic grammar of the game. A d20 test adds an ability modifier, proficiency when relevant, and other modifiers against a target number. Advantage and disadvantage handle favorable and unfavorable circumstances. Armor Class, attack rolls, saving throws, actions, reactions, damage, and conditions give players recognizable points of entry.

Familiarity reduced the number of concepts the book had to introduce at once. A player who already knows 5E can understand the core roll before learning how OSINT-6 handles intelligence records, sources, surveillance, exposure, cover identities, mission planning, or modern equipment. New players still receive the complete rules because the book doesn't require another rulebook at the table.

The license mattered too. SRD 5.2.1 provides a specific attribution statement and permits use under CC BY 4.0. We could identify which text and procedures came from that source, adapt them, and publish the resulting rulebook under a compatible framework. That created a cleaner boundary than relying on informal compatibility or scattered legacy material.

Starting with an SRD didn't mean accepting its entire design. It meant choosing a tested mechanical vocabulary, then deciding which parts supported modern espionage. Every retained element still had to survive a genre audit. Familiarity was useful only when it reduced learning cost without distorting the missions OSINT-6 was built to run.