diff --git a/src/logic/centerIndexes.js b/src/logic/centerIndexes.js
index ff0b4a7..b545ec9 100644
--- a/src/logic/centerIndexes.js
+++ b/src/logic/centerIndexes.js
@@ -1,6 +1,23 @@
 import {centerGrid} from "@skedwards88/word_logic";
 
 export function centerIndexes(indexes, gridSize) {
+  if (!Array.isArray(indexes) || !indexes.every(Number.isInteger)) {
+    throw new TypeError("The `indexes` input must be an array of integers");
+  }
+
+  if (!Number.isInteger(gridSize) || gridSize <= 0) {
+    throw new TypeError("The `gridSize` input must be an integer > 0");
+  }
+
+  if (indexes.some((index) => index > gridSize * gridSize - 1 || index < 0)) {
+    throw new Error("One of more of the indexes exceeds the grid size");
+  }
+
+  // return early if the index list is empty
+  if (indexes.length === 0) {
+    return indexes;
+  }
+
   // Arrange the flat indexes into a 2D grid of 0 and 1 where 1 represents an input index
   let grid = Array.from({length: gridSize}, () => Array(gridSize).fill(0));
   for (const index of indexes) {
diff --git a/src/logic/centerIndexes.test.js b/src/logic/centerIndexes.test.js
index 60ed2cb..0e5bd89 100644
--- a/src/logic/centerIndexes.test.js
+++ b/src/logic/centerIndexes.test.js
@@ -1,52 +1,102 @@
 import {centerIndexes} from "./centerIndexes";
 
 test("Given indexes in a grid, returns the indexes of the centered input indexes", () => {
-  const indexes = [11,15,17,20,21]
+  const indexes = [11, 15, 17, 20, 21];
 
   const centeredIndexes = centerIndexes(indexes, 5);
 
-  const expectedIndexes = [7,11,13,16,17]
+  const expectedIndexes = [7, 11, 13, 16, 17];
 
   expect(centeredIndexes).toEqual(expectedIndexes);
 });
 
-
 test("If the indexes can't be perfectly centered, errs towards the top left", () => {
-  const expectedIndexes = [8,13,14,15,20]
+  const expectedIndexes = [8, 13, 14, 15, 20];
 
-  const indexesBottomLeft = [19,24,25,26,31]
+  const indexesBottomLeft = [19, 24, 25, 26, 31];
 
   expect(centerIndexes(indexesBottomLeft, 6)).toEqual(expectedIndexes);
 
-  const indexesBottomRight = [22,27,28,29,34]
+  const indexesBottomRight = [22, 27, 28, 29, 34];
 
   expect(centerIndexes(indexesBottomRight, 6)).toEqual(expectedIndexes);
 
-  const indexesTopLeft = [1,6,7,8,13]
+  const indexesTopLeft = [1, 6, 7, 8, 13];
 
   expect(centerIndexes(indexesTopLeft, 6)).toEqual(expectedIndexes);
 
-  const indexesTopRight = [4,9,10,11,16]
+  const indexesTopRight = [4, 9, 10, 11, 16];
 
   expect(centerIndexes(indexesTopRight, 6)).toEqual(expectedIndexes);
 });
 
 test("If the indexes are already centered up/down, will still center right/left", () => {
-  const indexes = [6,10,12,15,16]
+  const indexes = [6, 10, 12, 15, 16];
 
   const centeredIndexes = centerIndexes(indexes, 5);
 
-  const expectedIndexes = [7,11,13,16,17]
+  const expectedIndexes = [7, 11, 13, 16, 17];
 
   expect(centeredIndexes).toEqual(expectedIndexes);
 });
 
 test("If the indexes are already centered right/left, will still center up/down", () => {
-  const indexes = [12,16,18,21,22]
+  const indexes = [12, 16, 18, 21, 22];
 
   const centeredIndexes = centerIndexes(indexes, 5);
 
-  const expectedIndexes = [7,11,13,16,17]
+  const expectedIndexes = [7, 11, 13, 16, 17];
 
   expect(centeredIndexes).toEqual(expectedIndexes);
 });
+
+test("Works on empty indexes", () => {
+  const indexes = [];
+
+  const centeredIndexes = centerIndexes(indexes, 5);
+
+  const expectedIndexes = [];
+
+  expect(centeredIndexes).toEqual(expectedIndexes);
+});
+
+test("Errors if the indexes input is not a list of ints", () => {
+  expect(() => centerIndexes(["A", "B", "C"], 5)).toThrow(
+    "The `indexes` input must be an array of integers",
+  );
+
+  expect(() =>
+    centerIndexes(
+      [
+        [1, 0, 1],
+        [0, 1, 1],
+        [0, 0, 0],
+      ],
+      5,
+    ),
+  ).toThrow("The `indexes` input must be an array of integers");
+});
+
+test("Errors if the gridSize input is not an int > 0", () => {
+  expect(() => centerIndexes([12, 16, 18, 21, 22], "6")).toThrow(
+    "The `gridSize` input must be an integer > 0",
+  );
+
+  expect(() => centerIndexes([12, 16, 18, 21, 22], 0)).toThrow(
+    "The `gridSize` input must be an integer > 0",
+  );
+});
+
+test("Errors if any of the indexes exceed the grid size", () => {
+  expect(() => centerIndexes([12, 16, 18, 21, 22], 4)).toThrow(
+    "One of more of the indexes exceeds the grid size",
+  );
+
+  expect(() => centerIndexes([-2, 12, 16, 18, 21, 22, 24], 6)).toThrow(
+    "One of more of the indexes exceeds the grid size",
+  );
+
+  expect(() => centerIndexes([2, 16, 18, 21, 22, 36], 6)).toThrow(
+    "One of more of the indexes exceeds the grid size",
+  );
+});
diff --git a/src/logic/shapesMatchQ.test.js b/src/logic/shapesMatchQ.test.js
new file mode 100644
index 0000000..bfb64c2
--- /dev/null
+++ b/src/logic/shapesMatchQ.test.js
@@ -0,0 +1,173 @@
+import {shapesMatchQ} from "./shapesMatchQ";
+
+test("Returns true if two sets of indexes form the same shape in a grid", () => {
+  expect(
+    shapesMatchQ({
+      indexes1: [11, 15, 17, 20, 21],
+      indexes2: [17, 11, 13, 16, 7],
+      gridSize: 5,
+    }),
+  ).toBe(true);
+
+  expect(
+    shapesMatchQ({
+      indexes1: [7, 11, 13, 16, 17],
+      indexes2: [6, 10, 12, 15, 16],
+      gridSize: 5,
+    }),
+  ).toBe(true);
+
+  expect(
+    shapesMatchQ({
+      indexes1: [12, 16, 18, 21, 22],
+      indexes2: [6, 15, 12, 10, 16],
+      gridSize: 5,
+    }),
+  ).toBe(true);
+
+  expect(
+    shapesMatchQ({
+      indexes1: [8, 13, 14, 15, 20],
+      indexes2: [19, 24, 25, 26, 31],
+      gridSize: 6,
+    }),
+  ).toBe(true);
+
+  expect(
+    shapesMatchQ({
+      indexes1: [22, 27, 28, 29, 34],
+      indexes2: [19, 24, 25, 26, 31],
+      gridSize: 6,
+    }),
+  ).toBe(true);
+
+  expect(
+    shapesMatchQ({
+      indexes1: [1, 6, 7, 8, 13],
+      indexes2: [19, 24, 31, 26, 25],
+      gridSize: 6,
+    }),
+  ).toBe(true);
+
+  expect(
+    shapesMatchQ({
+      indexes1: [8, 13, 14, 15, 20],
+      indexes2: [4, 9, 10, 11, 16],
+      gridSize: 6,
+    }),
+  ).toBe(true);
+});
+
+test("Returns false if two sets of indexes do not form the same shape in a grid", () => {
+  expect(
+    shapesMatchQ({
+      indexes1: [11, 15, 17, 20, 21],
+      indexes2: [7, 11, 13, 16, 18],
+      gridSize: 5,
+    }),
+  ).toBe(false);
+
+  expect(
+    shapesMatchQ({
+      indexes1: [7, 1, 13, 16, 17],
+      indexes2: [6, 10, 12, 15, 16],
+      gridSize: 5,
+    }),
+  ).toBe(false);
+
+  expect(
+    shapesMatchQ({
+      indexes1: [11, 12, 16, 18, 21, 22],
+      indexes2: [6, 10, 12, 15, 16],
+      gridSize: 5,
+    }),
+  ).toBe(false);
+
+  expect(
+    shapesMatchQ({
+      indexes1: [18, 13, 14, 15, 20],
+      indexes2: [19, 24, 25, 26, 31],
+      gridSize: 6,
+    }),
+  ).toBe(false);
+
+  expect(
+    shapesMatchQ({
+      indexes1: [2, 27, 28, 29, 34],
+      indexes2: [19, 24, 25, 26, 31],
+      gridSize: 6,
+    }),
+  ).toBe(false);
+});
+
+test("Returns works with empty arrays", () => {
+  expect(
+    shapesMatchQ({
+      indexes1: [],
+      indexes2: [],
+      gridSize: 5,
+    }),
+  ).toBe(true);
+
+  expect(
+    shapesMatchQ({
+      indexes1: [],
+      indexes2: [5, 6, 3],
+      gridSize: 5,
+    }),
+  ).toBe(false);
+});
+
+test("Errors if the indexes input is not a list of ints", () => {
+  expect(() =>
+    shapesMatchQ({
+      indexes1: ["7", "11", "13", 16, 17],
+      indexes2: [6, 10, 12, 15, 16],
+      gridSize: 5,
+    }),
+  ).toThrow("The `indexes` input must be an array of integers");
+
+  expect(() =>
+    shapesMatchQ({
+      indexes1: [[7, 11, 13, 16, 17]],
+      indexes2: [6, 10, 12, 15, 16],
+      gridSize: 5,
+    }),
+  ).toThrow("The `indexes` input must be an array of integers");
+});
+
+test("Errors if the gridSize input is not an int > 0", () => {
+  expect(() =>
+    shapesMatchQ({
+      indexes1: [7, 11, 13, 16, 17],
+      indexes2: [6, 10, 12, 15, 16],
+      gridSize: "5",
+    }),
+  ).toThrow("The `gridSize` input must be an integer > 0");
+
+  expect(() =>
+    shapesMatchQ({
+      indexes1: [7, 11, 13, 16, 17],
+      indexes2: [6, 10, 12, 15, 16],
+      gridSize: 0,
+    }),
+  ).toThrow("The `gridSize` input must be an integer > 0");
+});
+
+test("Errors if any of the indexes exceed the grid size", () => {
+  expect(() =>
+    shapesMatchQ({
+      indexes1: [7, 11, 13, 16, 25],
+      indexes2: [6, 10, 12, 15, 16],
+      gridSize: 5,
+    }),
+  ).toThrow("One of more of the indexes exceeds the grid size");
+
+  expect(() =>
+    shapesMatchQ({
+      indexes1: [-1, 11, 13, 16, 17],
+      indexes2: [6, 10, 12, 15, 16],
+      gridSize: 5,
+    }),
+  ).toThrow("One of more of the indexes exceeds the grid size");
+});