Look up whether a named entity exists in the loaded rulesets' content registries. exit_code 0 = known content (categories in payload); 2 = unknown or third-party content, honestly refused.

Compose an attack roll's Advantage/Disadvantage from both combatants' conditions and distance (Prone's 5-foot flip, Blinded, Restrained, Paralyzed, Stunned, Invisible with the seen exception, the Grappled attacker rule). Exhaustion is returned as a flat modifier, never Advantage. Genuinely ambiguous rules text (e.g. a seen Invisible target) returns cannot-adjudicate with the ambiguous sentence cited.

The reducer (fold): apply one declared event to a state object and receive the verdict plus the stamped next_state (lineage: predecessor hash, causing event, rule ids, rule-vs-ruling kind). Event types: turn-start (budgets reset, Reaction returns), round-advance, action / bonus-action / reaction / free-interaction / move / stand-up (validated against budgets and conditions; may carry spell:{level} and concentration_on), condition-gained, condition-ended, ruling (GM discretion — recorded and tagged as discretion, never as a rule). srdcheck never produces an event, never advances time on its own, never generates randomness: the caller owns the loop; this is the fold.

Adjudicate one proposed use of the Mage Hand cantrip: granted uses (manipulate, open unlocked, stow/retrieve, pour), prohibitions (attack, activate magic items), the 10-pound carry limit and 30-foot range leash. Uses outside the text's can/can't lists return cannot-adjudicate — the GM's call, honestly labeled.

Is taking a Reaction legal right now? Reactions refresh at the start of your own turn (not the round) and are usable on your own turn.

Compose net Advantage/Disadvantage from lists of sources: multiple sources never add dice, and any Advantage plus any Disadvantage yields a straight single-d20 roll regardless of counts. Optionally notes the reroll-one-die-only rule.

Enumerate what remains legal this turn given the same state shape as turn.plan (no plan). Options carry feet_remaining, stand-up cost, crawl mode, and spell-slot availability. Consistency-tested against turn.plan: everything enumerated is accepted, everything past a boundary rejected.

Judge a whole proposed turn under SRD 5.2.1 ACTION ECONOMY: action/bonus-action/reaction/free-interaction budgets, movement (crawling, standing from Prone, Grappled speed 0), Incapacitated, and the one-spell-slot-per-turn rule. Returns legal/illegal/cannot-adjudicate with citations; illegal verdicts name the first offending step. Scope: this checks the turn's economy only — it does NOT verify that a feature grants a given action (e.g. two-weapon fighting or Extra Attack prerequisites). Unmodeled conditions and out-of-range inputs (negative speed, spell level >9) return exit 2 rather than a guess.

Judge one proposed tic-tac-toe move. Board is a 9-character string of X, O, and . (dot = empty), cells 1-9 left-to-right top-to-bottom. Checks turn order, cell validity, occupancy, and whether the game has already ended.

Enumerate the legal moves for a player on a board (same encoding as ttt.move). Empty when it is not the player's turn or the game has ended.