diff --git a/packages/workflow-protocol/__tests__/jsonata-moderator.test.ts b/packages/workflow-protocol/__tests__/jsonata-moderator.test.ts
new file mode 100644
index 0000000..461ccc4
--- /dev/null
+++ b/packages/workflow-protocol/__tests__/jsonata-moderator.test.ts
@@ -0,0 +1,284 @@
+import { describe, expect, test } from "bun:test";
+
+import type { ModeratorRule } from "../src/jsonata-moderator.js";
+import { evaluateModerator } from "../src/jsonata-moderator.js";
+import type { ModeratorContext, StartStep } from "../src/types.js";
+import { END, START } from "../src/types.js";
+
+// ── Helpers ─────────────────────────────────────────────────────────
+
+const BASE_START: StartStep = {
+  role: START,
+  content: "test task",
+  meta: {},
+  timestamp: 1000,
+  parentState: null,
+};
+
+function makeCtx(
+  steps: Array<{ role: string; meta: Record<string, unknown> }>,
+  overrides: Partial<ModeratorContext> = {},
+): ModeratorContext {
+  return {
+    threadId: "01JTESTTHREADID000",
+    depth: 0,
+    bundleHash: "TESTHASH00001",
+    start: BASE_START,
+    steps: steps.map((s, i) => ({
+      ...s,
+      contentHash: `hash-${i}`,
+      refs: [],
+      timestamp: 2000 + i,
+    })) as ModeratorContext["steps"],
+    ...overrides,
+  };
+}
+
+// ── Step 1: FALLBACK rule (when=null) always matches ────────────────
+
+describe("Step 1: FALLBACK rule", () => {
+  test("when=null always matches → returns rule.to", async () => {
+    const rules: ModeratorRule[] = [{ from: START, to: "planner", when: null }];
+    const result = await evaluateModerator(rules, makeCtx([]));
+    expect(result).toBe("planner");
+  });
+});
+
+// ── Step 2: No matching rules → __end__ ─────────────────────────────
+
+describe("Step 2: no matching rules", () => {
+  test("empty steps, no rule for __start__ → __end__", async () => {
+    const rules: ModeratorRule[] = [{ from: "planner", to: "coder", when: null }];
+    const result = await evaluateModerator(rules, makeCtx([]));
+    expect(result).toBe(END);
+  });
+
+  test("current state has no matching from rules → __end__", async () => {
+    const rules: ModeratorRule[] = [{ from: START, to: "planner", when: null }];
+    const result = await evaluateModerator(rules, makeCtx([{ role: "planner", meta: {} }]));
+    expect(result).toBe(END);
+  });
+});
+
+// ── Step 3: JSONata condition — truthy → match ────────────────────
+
+describe("Step 3: JSONata condition evaluation", () => {
+  test("truthy expression matches and returns rule.to", async () => {
+    const rules: ModeratorRule[] = [
+      {
+        from: "planner",
+        to: END,
+        when: "steps[role='planner'].meta.status = 'aborted'",
+      },
+      { from: "planner", to: "coder", when: null },
+    ];
+    const ctx = makeCtx([{ role: "planner", meta: { status: "aborted" } }]);
+    expect(await evaluateModerator(rules, ctx)).toBe(END);
+  });
+
+  test("falsy expression skips to next rule (FALLBACK)", async () => {
+    const rules: ModeratorRule[] = [
+      {
+        from: "planner",
+        to: END,
+        when: "steps[role='planner'].meta.status = 'aborted'",
+      },
+      { from: "planner", to: "coder", when: null },
+    ];
+    const ctx = makeCtx([{ role: "planner", meta: { status: "planned" } }]);
+    expect(await evaluateModerator(rules, ctx)).toBe("coder");
+  });
+});
+
+// ── Step 4: plannerAborted condition ─────────────────────────────
+
+describe("Step 4: plannerAborted", () => {
+  const plannerAbortedRules: ModeratorRule[] = [
+    {
+      from: "planner",
+      to: END,
+      when: "steps[role='planner'].meta.status = 'aborted'",
+    },
+    { from: "planner", to: "coder", when: null },
+  ];
+
+  test("planner aborted → __end__", async () => {
+    const ctx = makeCtx([{ role: "planner", meta: { status: "aborted" } }]);
+    expect(await evaluateModerator(plannerAbortedRules, ctx)).toBe(END);
+  });
+
+  test("planner planned → coder", async () => {
+    const ctx = makeCtx([{ role: "planner", meta: { status: "planned", phases: [] } }]);
+    expect(await evaluateModerator(plannerAbortedRules, ctx)).toBe("coder");
+  });
+});
+
+// ── Step 5: reviewApproved / testsPassed (negative index) ────────
+
+describe("Step 5: last-step conditions", () => {
+  const rules: ModeratorRule[] = [
+    {
+      from: "reviewer",
+      to: "tester",
+      when: "steps[-1].meta.status = 'approved'",
+    },
+    { from: "reviewer", to: "coder", when: null },
+    {
+      from: "tester",
+      to: "committer",
+      when: "steps[-1].meta.status = 'passed'",
+    },
+    { from: "tester", to: "coder", when: null },
+  ];
+
+  test("reviewer approved → tester", async () => {
+    const ctx = makeCtx([{ role: "reviewer", meta: { status: "approved" } }]);
+    expect(await evaluateModerator(rules, ctx)).toBe("tester");
+  });
+
+  test("reviewer changes-requested → coder", async () => {
+    const ctx = makeCtx([{ role: "reviewer", meta: { status: "changes-requested" } }]);
+    expect(await evaluateModerator(rules, ctx)).toBe("coder");
+  });
+
+  test("tester passed → committer", async () => {
+    const ctx = makeCtx([{ role: "tester", meta: { status: "passed" } }]);
+    expect(await evaluateModerator(rules, ctx)).toBe("committer");
+  });
+
+  test("tester failed → coder", async () => {
+    const ctx = makeCtx([{ role: "tester", meta: { status: "failed" } }]);
+    expect(await evaluateModerator(rules, ctx)).toBe("coder");
+  });
+});
+
+// ── Step 6: allPhasesComplete condition ──────────────────────────
+
+describe("Step 6: allPhasesComplete", () => {
+  // The JSONata expression checks if all planned phase hashes appear in coder completedPhase values.
+  // Approximation using $count approach:
+  // Use JSONata 'in' operator inside $filter to check if each planned phase hash
+  // appears in the coder completedPhase values.
+  const allPhasesExpr =
+    "$count(steps[role='planner'].meta.phases) = 0 or $count(steps[role='planner'].meta.phases ~> $filter(function($p) { $p.hash in steps[role='coder'].meta.completedPhase })) >= $count(steps[role='planner'].meta.phases)";
+
+  const rules: ModeratorRule[] = [
+    { from: "coder", to: "reviewer", when: allPhasesExpr },
+    { from: "coder", to: "coder", when: null },
+  ];
+
+  test("no phases (empty array) → all complete → reviewer", async () => {
+    const ctx = makeCtx([
+      { role: "planner", meta: { status: "planned", phases: [] } },
+      { role: "coder", meta: { completedPhase: "PHASE001" } },
+    ]);
+    expect(await evaluateModerator(rules, ctx)).toBe("reviewer");
+  });
+
+  test("all phases completed → reviewer", async () => {
+    const ctx = makeCtx([
+      {
+        role: "planner",
+        meta: {
+          status: "planned",
+          phases: [{ hash: "PHASE001" }, { hash: "PHASE002" }],
+        },
+      },
+      { role: "coder", meta: { completedPhase: "PHASE001" } },
+      { role: "coder", meta: { completedPhase: "PHASE002" } },
+    ]);
+    expect(await evaluateModerator(rules, ctx)).toBe("reviewer");
+  });
+
+  test("not all phases completed → coder (loop)", async () => {
+    const ctx = makeCtx([
+      {
+        role: "planner",
+        meta: {
+          status: "planned",
+          phases: [{ hash: "PHASE001" }, { hash: "PHASE002" }],
+        },
+      },
+      { role: "coder", meta: { completedPhase: "PHASE001" } },
+    ]);
+    expect(await evaluateModerator(rules, ctx)).toBe("coder");
+  });
+});
+
+// ── Step 7: Full develop workflow routing table ───────────────────
+
+describe("Step 7: full develop workflow routing", () => {
+  const allPhasesExpr =
+    "$count(steps[role='planner'].meta.phases) = 0 or $count(steps[role='planner'].meta.phases ~> $filter(function($p) { $p.hash in steps[role='coder'].meta.completedPhase })) >= $count(steps[role='planner'].meta.phases)";
+
+  const rules: ModeratorRule[] = [
+    { from: START, to: "planner", when: null },
+    { from: "planner", to: END, when: "steps[role='planner'].meta.status = 'aborted'" },
+    { from: "planner", to: "coder", when: null },
+    { from: "coder", to: "reviewer", when: allPhasesExpr },
+    { from: "coder", to: "coder", when: null },
+    { from: "reviewer", to: "tester", when: "steps[-1].meta.status = 'approved'" },
+    { from: "reviewer", to: "coder", when: null },
+    { from: "tester", to: "committer", when: "steps[-1].meta.status = 'passed'" },
+    { from: "tester", to: "coder", when: null },
+    { from: "committer", to: END, when: null },
+  ];
+
+  test("initial state → planner", async () => {
+    expect(await evaluateModerator(rules, makeCtx([]))).toBe("planner");
+  });
+
+  test("planner planned, no phases → coder", async () => {
+    const ctx = makeCtx([{ role: "planner", meta: { status: "planned", phases: [] } }]);
+    expect(await evaluateModerator(rules, ctx)).toBe("coder");
+  });
+
+  test("planner aborted → __end__", async () => {
+    const ctx = makeCtx([{ role: "planner", meta: { status: "aborted" } }]);
+    expect(await evaluateModerator(rules, ctx)).toBe(END);
+  });
+
+  test("coder completed single phase → reviewer", async () => {
+    const ctx = makeCtx([
+      { role: "planner", meta: { status: "planned", phases: [{ hash: "PH1" }] } },
+      { role: "coder", meta: { completedPhase: "PH1" } },
+    ]);
+    expect(await evaluateModerator(rules, ctx)).toBe("reviewer");
+  });
+
+  test("coder incomplete phases → coder", async () => {
+    const ctx = makeCtx([
+      {
+        role: "planner",
+        meta: { status: "planned", phases: [{ hash: "PH1" }, { hash: "PH2" }] },
+      },
+      { role: "coder", meta: { completedPhase: "PH1" } },
+    ]);
+    expect(await evaluateModerator(rules, ctx)).toBe("coder");
+  });
+
+  test("reviewer approved → tester", async () => {
+    const ctx = makeCtx([{ role: "reviewer", meta: { status: "approved" } }]);
+    expect(await evaluateModerator(rules, ctx)).toBe("tester");
+  });
+
+  test("reviewer rejected → coder", async () => {
+    const ctx = makeCtx([{ role: "reviewer", meta: { status: "changes-requested" } }]);
+    expect(await evaluateModerator(rules, ctx)).toBe("coder");
+  });
+
+  test("tester passed → committer", async () => {
+    const ctx = makeCtx([{ role: "tester", meta: { status: "passed" } }]);
+    expect(await evaluateModerator(rules, ctx)).toBe("committer");
+  });
+
+  test("tester failed → coder", async () => {
+    const ctx = makeCtx([{ role: "tester", meta: { status: "failed" } }]);
+    expect(await evaluateModerator(rules, ctx)).toBe("coder");
+  });
+
+  test("committer done → __end__", async () => {
+    const ctx = makeCtx([{ role: "committer", meta: {} }]);
+    expect(await evaluateModerator(rules, ctx)).toBe(END);
+  });
+});
diff --git a/packages/workflow-protocol/package.json b/packages/workflow-protocol/package.json
index 8262a95..bb81851 100644
--- a/packages/workflow-protocol/package.json
+++ b/packages/workflow-protocol/package.json
@@ -28,5 +28,8 @@
   },
   "publishConfig": {
     "access": "public"
+  },
+  "dependencies": {
+    "jsonata": "^2.2.0"
   }
 }
diff --git a/packages/workflow-protocol/src/index.ts b/packages/workflow-protocol/src/index.ts
index 9e30a79..9ae5b42 100644
--- a/packages/workflow-protocol/src/index.ts
+++ b/packages/workflow-protocol/src/index.ts
@@ -54,3 +54,8 @@ export { END, START } from "./types.js";
 // ── Constructor functions ──────────────────────────────────────────
 
 export { err, ok } from "./result.js";
+
+// ── JSONata moderator ──────────────────────────────────────────────
+
+export type { ModeratorRule } from "./jsonata-moderator.js";
+export { evaluateModerator } from "./jsonata-moderator.js";
diff --git a/packages/workflow-protocol/src/jsonata-moderator.ts b/packages/workflow-protocol/src/jsonata-moderator.ts
new file mode 100644
index 0000000..bc3144a
--- /dev/null
+++ b/packages/workflow-protocol/src/jsonata-moderator.ts
@@ -0,0 +1,66 @@
+import jsonata from "jsonata";
+
+import type { ModeratorContext, RoleMeta, StartStep } from "./types.js";
+import { END, START } from "./types.js";
+
+// ── Types ───────────────────────────────────────────────────────────
+
+export type ModeratorRule = {
+  from: string;
+  to: string;
+  when: string | null;
+};
+
+type JsonataContext = {
+  threadId: string;
+  depth: number;
+  start: StartStep;
+  steps: ReadonlyArray<{ role: string; meta: Record<string, unknown> }>;
+};
+
+// ── Evaluator ───────────────────────────────────────────────────────
+
+/**
+ * Evaluate a JSONata-based moderator rule set against the given thread context.
+ * Returns the next role name or '__end__'.
+ */
+export async function evaluateModerator(
+  rules: ReadonlyArray<ModeratorRule>,
+  context: ModeratorContext,
+): Promise<string> {
+  const lastStep = context.steps.length > 0 ? context.steps[context.steps.length - 1] : null;
+  const currentState: string = lastStep ? lastStep.role : START;
+
+  const matching = rules.filter((r) => r.from === currentState);
+
+  const jsonataCtx: JsonataContext = {
+    threadId: context.threadId,
+    depth: context.depth,
+    start: context.start,
+    steps: context.steps as ReadonlyArray<{ role: string; meta: Record<string, unknown> }>,
+  };
+
+  for (const rule of matching) {
+    if (rule.when === null) {
+      return rule.to;
+    }
+
+    const expr = jsonata(rule.when);
+    const result = await expr.evaluate(jsonataCtx);
+
+    if (result) {
+      return rule.to;
+    }
+  }
+
+  return END;
+}
+
+// ── Context helper ──────────────────────────────────────────────────
+
+/** Build a ModeratorContext from its constituent parts (convenience for tests / callers). */
+export function makeModeratorContext<M extends RoleMeta>(
+  ctx: ModeratorContext<M>,
+): ModeratorContext<M> {
+  return ctx;
+}