diff --git a/src/config.ts b/src/config.ts
index b752f8b..6a64210 100644
--- a/src/config.ts
+++ b/src/config.ts
@@ -1,4 +1,4 @@
-import type { Config } from "./types.js";
+import type { Config, NudgeConfig } from "./types.js";
 
 export function defaultConfig(
   modelContextLimit: number,
@@ -72,5 +72,33 @@ export function validateConfig(config: Config): string[] {
   if (config.tiers.tier3Trigger <= config.tiers.tier2Trigger) {
     errors.push("tiers.tier3Trigger must be greater than tiers.tier2Trigger");
   }
+  const nonNegative: Array<
+    keyof Pick<
+      NudgeConfig,
+      "growthRatio" | "growthFloor" | "minGrowthFloor" | "minGrowthRatio"
+    >
+  > = ["growthRatio", "growthFloor", "minGrowthFloor", "minGrowthRatio"];
+  for (const field of nonNegative) {
+    const v = config.nudge[field];
+    if (!Number.isFinite(v)) {
+      errors.push(`nudge.${field} must be a finite number`);
+    } else if (v < 0) {
+      errors.push(`nudge.${field} must be >= 0`);
+    }
+  }
+  if (!Number.isFinite(config.nudge.growthCap)) {
+    errors.push("nudge.growthCap must be a finite number");
+  } else if (
+    Number.isFinite(config.nudge.growthFloor) &&
+    config.nudge.growthCap < config.nudge.growthFloor
+  ) {
+    errors.push("nudge.growthCap must be >= nudge.growthFloor");
+  }
+  const emergency = config.nudge.emergencyThresholdPct;
+  if (!Number.isFinite(emergency)) {
+    errors.push("nudge.emergencyThresholdPct must be a finite number");
+  } else if (emergency <= 0 || emergency > 1) {
+    errors.push("nudge.emergencyThresholdPct must be in (0, 1]");
+  }
   return errors;
 }
diff --git a/tests/sync-config.test.ts b/tests/sync-config.test.ts
index 76fd5d2..a8444aa 100644
--- a/tests/sync-config.test.ts
+++ b/tests/sync-config.test.ts
@@ -93,3 +93,111 @@ test("validateConfig flags min > max nudge thresholds", () => {
 test("validateConfig passes for default config", () => {
   assert.deepEqual(validateConfig(defaultConfig(200000)), []);
 });
+
+// Issue #46 scope: tier2GrowthMultiplier is intentionally left unvalidated.
+type NudgeNumberField =
+  | "growthRatio"
+  | "growthFloor"
+  | "growthCap"
+  | "minGrowthFloor"
+  | "minGrowthRatio"
+  | "emergencyThresholdPct";
+
+test("validateConfig rejects negative nudge growth values", () => {
+  const cases: Array<{ field: NudgeNumberField; value: number }> = [
+    { field: "growthRatio", value: -0.1 },
+    { field: "growthFloor", value: -1 },
+    { field: "minGrowthFloor", value: -1 },
+    { field: "minGrowthRatio", value: -0.1 },
+  ];
+  for (const { field, value } of cases) {
+    const cfg = defaultConfig(200000);
+    cfg.nudge[field] = value;
+    assert.ok(
+      validateConfig(cfg).some((e) => e.includes(`nudge.${field}`)),
+      `expected nudge.${field} to be rejected`,
+    );
+  }
+});
+
+test("validateConfig rejects non-finite nudge numbers", () => {
+  const cases: Array<{ field: NudgeNumberField; value: number }> = [
+    { field: "growthRatio", value: NaN },
+    { field: "growthFloor", value: Infinity },
+    { field: "growthCap", value: Infinity },
+    { field: "minGrowthFloor", value: NaN },
+    { field: "minGrowthRatio", value: Infinity },
+    { field: "emergencyThresholdPct", value: NaN },
+  ];
+  for (const { field, value } of cases) {
+    const cfg = defaultConfig(200000);
+    cfg.nudge[field] = value;
+    assert.ok(
+      validateConfig(cfg).some((e) => e.includes(`nudge.${field}`)),
+      `expected non-finite nudge.${field} to be rejected`,
+    );
+  }
+});
+
+test("validateConfig accepts zero for non-negative nudge fields", () => {
+  const fields: NudgeNumberField[] = [
+    "growthRatio",
+    "growthFloor",
+    "minGrowthFloor",
+    "minGrowthRatio",
+  ];
+  for (const field of fields) {
+    const cfg = defaultConfig(200000);
+    cfg.nudge[field] = 0;
+    assert.deepEqual(
+      validateConfig(cfg),
+      [],
+      `expected nudge.${field}=0 to be valid`,
+    );
+  }
+});
+
+test("validateConfig rejects growthCap below growthFloor", () => {
+  const cfg = defaultConfig(200000);
+  cfg.nudge.growthFloor = 100;
+  cfg.nudge.growthCap = 99;
+  assert.ok(
+    validateConfig(cfg).some((e) => e.includes("nudge.growthCap")),
+  );
+});
+
+test("validateConfig accepts growthCap equal to growthFloor", () => {
+  const cfg = defaultConfig(200000);
+  cfg.nudge.growthFloor = 100;
+  cfg.nudge.growthCap = 100;
+  assert.deepEqual(validateConfig(cfg), []);
+});
+
+test("validateConfig rejects emergencyThresholdPct of 0", () => {
+  const cfg = defaultConfig(200000);
+  cfg.nudge.emergencyThresholdPct = 0;
+  assert.ok(
+    validateConfig(cfg).some((e) => e.includes("nudge.emergencyThresholdPct")),
+  );
+});
+
+test("validateConfig rejects emergencyThresholdPct above 1", () => {
+  const cfg = defaultConfig(200000);
+  cfg.nudge.emergencyThresholdPct = 1.01;
+  assert.ok(
+    validateConfig(cfg).some((e) => e.includes("nudge.emergencyThresholdPct")),
+  );
+});
+
+test("validateConfig accepts emergencyThresholdPct of 1", () => {
+  const cfg = defaultConfig(200000);
+  cfg.nudge.emergencyThresholdPct = 1;
+  assert.deepEqual(validateConfig(cfg), []);
+});
+
+test("validateConfig does not reject finite ratios above 1", () => {
+  const cfg = defaultConfig(200000);
+  cfg.nudge.growthRatio = 2;
+  cfg.nudge.minGrowthRatio = 2;
+  assert.deepEqual(validateConfig(cfg), []);
+});