diff --git a/pkg/spec-api/src/actions.ts b/pkg/spec-api/src/actions.ts
new file mode 100644
index 0000000..2d0a758
--- /dev/null
+++ b/pkg/spec-api/src/actions.ts
@@ -0,0 +1,36 @@
+import type {
+  AccessibilityElement,
+  Action,
+  ActionGenerator,
+  InputTextAction,
+  TapAction,
+  WeightedEntry,
+} from "./types.ts";
+
+export function actions(generator: () => Action[]): ActionGenerator {
+  return globalThis.__uatu__.actions(generator);
+}
+
+export function weighted(...entries: WeightedEntry[]): ActionGenerator {
+  return globalThis.__uatu__.weighted(...entries);
+}
+
+export function Tap(parameters: { on: string | AccessibilityElement }): TapAction {
+  return globalThis.__uatu__.tap(parameters);
+}
+
+export function InputText(parameters: { into: string | AccessibilityElement; text: string }): InputTextAction {
+  return globalThis.__uatu__.inputText(parameters);
+}
+
+export const taps: ActionGenerator = new Proxy({} as ActionGenerator, {
+  get(_target, property) {
+    return (globalThis.__uatu__.taps as unknown as Record<string | symbol, unknown>)[property];
+  },
+});
+
+export const swipes: ActionGenerator = new Proxy({} as ActionGenerator, {
+  get(_target, property) {
+    return (globalThis.__uatu__.swipes as unknown as Record<string | symbol, unknown>)[property];
+  },
+});
diff --git a/pkg/spec-api/src/extract.ts b/pkg/spec-api/src/extract.ts
new file mode 100644
index 0000000..a0181d7
--- /dev/null
+++ b/pkg/spec-api/src/extract.ts
@@ -0,0 +1,5 @@
+import type { Extracted, State } from "./types.ts";
+
+export function extract<T>(getter: (state: State) => T): Extracted<T> {
+  return globalThis.__uatu__.extract(getter);
+}
diff --git a/pkg/spec-api/src/index.ts b/pkg/spec-api/src/index.ts
new file mode 100644
index 0000000..b74ca53
--- /dev/null
+++ b/pkg/spec-api/src/index.ts
@@ -0,0 +1,17 @@
+export type {
+  AccessibilityElement,
+  AccessibilityTree,
+  Action,
+  ActionGenerator,
+  Extracted,
+  Formula,
+  InputTextAction,
+  Snapshots,
+  State,
+  TapAction,
+  WeightedEntry,
+} from "./types.ts";
+
+export { extract } from "./extract.ts";
+export { always } from "./ltl.ts";
+export { Tap, InputText, actions, weighted, taps, swipes } from "./actions.ts";
diff --git a/pkg/spec-api/src/ltl.ts b/pkg/spec-api/src/ltl.ts
new file mode 100644
index 0000000..381e3af
--- /dev/null
+++ b/pkg/spec-api/src/ltl.ts
@@ -0,0 +1,5 @@
+import type { Formula } from "./types.ts";
+
+export function always(predicate: () => boolean): Formula {
+  return globalThis.__uatu__.always(predicate);
+}
diff --git a/pkg/spec-api/src/types.ts b/pkg/spec-api/src/types.ts
new file mode 100644
index 0000000..1b02c16
--- /dev/null
+++ b/pkg/spec-api/src/types.ts
@@ -0,0 +1,53 @@
+export type Snapshots = Record<string, unknown>;
+
+export interface AccessibilityElement {
+  id?: string;
+  text?: string;
+  bounds?: { left: number; top: number; right: number; bottom: number };
+}
+
+export interface AccessibilityTree {
+  find(selector: string): AccessibilityElement | undefined;
+  findAll(selector: string): AccessibilityElement[];
+}
+
+export interface State {
+  snapshots: Snapshots;
+  ax: AccessibilityTree;
+}
+
+export interface Extracted<T> {
+  readonly current: T;
+  readonly previous: T | undefined;
+}
+
+export type TapAction = { kind: "Tap"; on: string | AccessibilityElement };
+export type InputTextAction = { kind: "InputText"; into: string | AccessibilityElement; text: string };
+export type Action = TapAction | InputTextAction;
+
+export interface ActionGenerator {
+  readonly __uatuActionGenerator: true;
+  generate(): Action[];
+}
+
+export interface Formula {
+  readonly __uatuFormula: true;
+}
+
+export interface UatuRuntime {
+  extract: <T>(getter: (state: State) => T) => Extracted<T>;
+  always: (predicate: () => boolean) => Formula;
+  actions: (generator: () => Action[]) => ActionGenerator;
+  weighted: (...entries: WeightedEntry[]) => ActionGenerator;
+  tap: (parameters: { on: string | AccessibilityElement }) => TapAction;
+  inputText: (parameters: { into: string | AccessibilityElement; text: string }) => InputTextAction;
+  taps: ActionGenerator;
+  swipes: ActionGenerator;
+}
+
+export type WeightedEntry = readonly [number, ActionGenerator];
+
+declare global {
+  // eslint-disable-next-line no-var
+  var __uatu__: UatuRuntime;
+}