diff --git a/packages/stack-shared/src/utils/errors.tsx b/packages/stack-shared/src/utils/errors.tsx
index 66c7c253e0..83702c6fc4 100644
--- a/packages/stack-shared/src/utils/errors.tsx
+++ b/packages/stack-shared/src/utils/errors.tsx
@@ -82,10 +82,7 @@ StackAssertionError.prototype.name = "StackAssertionError";
 
 export function errorToNiceString(error: unknown): string {
   if (!(error instanceof Error)) return `${typeof error}<${nicify(error)}>`;
-  let stack = error.stack ?? "";
-  const toString = error.toString();
-  if (!stack.startsWith(toString)) stack = `${toString}\n${stack}`;  // some browsers don't include the error message in the stack, some do
-  return `${stack} ${nicify(Object.fromEntries(Object.entries(error)), { maxDepth: 8 })}`;
+  return nicify(error, { maxDepth: 8 });
 }
 
 
diff --git a/packages/stack-shared/src/utils/hashes.tsx b/packages/stack-shared/src/utils/hashes.tsx
index 4dd8fdbe04..82d0fa1372 100644
--- a/packages/stack-shared/src/utils/hashes.tsx
+++ b/packages/stack-shared/src/utils/hashes.tsx
@@ -17,7 +17,7 @@ export async function hashPassword(password: string) {
   return await bcrypt.hash(password, salt);
 }
 
-export async function comparePassword(password: string, hash: string) {
+export async function comparePassword(password: string, hash: string): Promise<boolean> {
   switch (await getPasswordHashAlgorithm(hash)) {
     case "bcrypt": {
       return await bcrypt.compare(password, hash);
diff --git a/packages/stack-shared/src/utils/results.tsx b/packages/stack-shared/src/utils/results.tsx
index 41a0c79cb2..73a2e8192e 100644
--- a/packages/stack-shared/src/utils/results.tsx
+++ b/packages/stack-shared/src/utils/results.tsx
@@ -1,5 +1,5 @@
 import { wait } from "./promises";
-import { deindent } from "./strings";
+import { deindent, nicify } from "./strings";
 
 export type Result<T, E = unknown> =
   | {
@@ -305,7 +305,7 @@ import.meta.vitest?.test("mapResult", ({ expect }) => {
 
 class RetryError extends AggregateError {
   constructor(public readonly errors: unknown[]) {
-    const strings = errors.map(e => String(e));
+    const strings = errors.map(e => nicify(e));
     const isAllSame = strings.length > 1 && strings.every(s => s === strings[0]);
     super(
       errors,
@@ -314,10 +314,10 @@ class RetryError extends AggregateError {
       
       ${isAllSame ? deindent`
         Attempts 1-${errors.length}:
-          ${errors[0]}
-      ` : errors.map((e, i) => deindent`
+          ${strings[0]}
+      ` : strings.map((s, i) => deindent`
           Attempt ${i + 1}:
-            ${e}
+            ${s}
         `).join("\n\n")}
       `,
       { cause: errors[errors.length - 1] }
diff --git a/packages/stack-shared/src/utils/strings.nicify.test.ts b/packages/stack-shared/src/utils/strings.nicify.test.ts
new file mode 100644
index 0000000000..a105ceaf02
--- /dev/null
+++ b/packages/stack-shared/src/utils/strings.nicify.test.ts
@@ -0,0 +1,245 @@
+import { describe, expect, test } from "vitest";
+import { NicifyOptions, deindent, nicify } from "./strings";
+
+describe("nicify", () => {
+  describe("primitive values", () => {
+    test("numbers", () => {
+      expect(nicify(123)).toBe("123");
+      expect(nicify(123n)).toBe("123n");
+    });
+
+    test("strings", () => {
+      expect(nicify("hello")).toBe('"hello"');
+    });
+
+    test("booleans", () => {
+      expect(nicify(true)).toBe("true");
+      expect(nicify(false)).toBe("false");
+    });
+
+    test("null and undefined", () => {
+      expect(nicify(null)).toBe("null");
+      expect(nicify(undefined)).toBe("undefined");
+    });
+
+    test("symbols", () => {
+      expect(nicify(Symbol("test"))).toBe("Symbol(test)");
+    });
+  });
+
+  describe("arrays", () => {
+    test("empty array", () => {
+      expect(nicify([])).toBe("[]");
+    });
+
+    test("single-element array", () => {
+      expect(nicify([1])).toBe("[1]");
+    });
+
+    test("single-element array with long content", () => {
+      expect(nicify(["123123123123123"])).toBe('["123123123123123"]');
+    });
+
+    test("flat array", () => {
+      expect(nicify([1, 2, 3])).toBe("[1, 2, 3]");
+    });
+
+    test("longer array", () => {
+      expect(nicify([10000, 2, 3])).toBe(deindent`
+        [
+          10000,
+          2,
+          3,
+        ]
+      `);
+    });
+
+    test("nested array", () => {
+      expect(nicify([1, [2, 3]])).toBe(deindent`
+        [
+          1,
+          [2, 3],
+        ]
+      `);
+    });
+  });
+
+  describe("objects", () => {
+    test("empty object", () => {
+      expect(nicify({})).toBe("{}");
+    });
+
+    test("simple object", () => {
+      expect(nicify({ a: 1 })).toBe('{ "a": 1 }');
+    });
+
+    test("multiline object", () => {
+      expect(nicify({ a: 1, b: 2 })).toBe(deindent`
+        {
+          "a": 1,
+          "b": 2,
+        }
+      `);
+    });
+  });
+
+  describe("custom classes", () => {
+    test("class instance", () => {
+      class TestClass {
+        constructor(public value: number) {}
+      }
+      expect(nicify(new TestClass(42))).toBe('TestClass { "value": 42 }');
+    });
+  });
+
+  describe("built-in objects", () => {
+    test("URL", () => {
+      expect(nicify(new URL("https://example.com"))).toBe('URL("https://example.com/")');
+    });
+
+    test("TypedArrays", () => {
+      expect(nicify(new Uint8Array([1, 2, 3]))).toBe("Uint8Array([1,2,3])");
+      expect(nicify(new Int32Array([1, 2, 3]))).toBe("Int32Array([1,2,3])");
+    });
+
+    test("Error objects", () => {
+      const error = new Error("test error");
+      const nicifiedError = nicify({ error });
+      expect(nicifiedError).toMatch(new RegExp(deindent`
+        ^\{
+          "error": Error: test error
+            Stack:
+              at (.|\\n)*
+        \}$
+      `));
+    });
+
+    test("Error objects with cause and an extra property", () => {
+      const error = new Error("test error", { cause: new Error("cause") });
+      (error as any).extra = "something";
+      const nicifiedError = nicify(error, { lineIndent: "--" });
+      expect(nicifiedError).toMatch(new RegExp(deindent`
+        ^Error: test error
+        --Stack:
+        ----at (.|\\n)+
+        --Extra properties: \{ "extra": "something" \}
+        --Cause:
+        ----Error: cause
+        ------Stack:
+        --------at (.|\\n)+$
+      `));
+    });
+
+    test("Headers", () => {
+      const headers = new Headers();
+      headers.append("Content-Type", "application/json");
+      headers.append("Accept", "text/plain");
+      expect(nicify(headers)).toBe(deindent`
+        Headers {
+          "accept": "text/plain",
+          "content-type": "application/json",
+        }`
+      );
+    });
+  });
+
+  describe("multiline strings", () => {
+    test("basic multiline", () => {
+      expect(nicify("line1\nline2")).toBe('deindent`\n  line1\n  line2\n`');
+    });
+
+    test("multiline with trailing newline", () => {
+      expect(nicify("line1\nline2\n")).toBe('deindent`\n  line1\n  line2\n` + "\\n"');
+    });
+  });
+
+  describe("circular references", () => {
+    test("object with self reference", () => {
+      const circular: any = { a: 1 };
+      circular.self = circular;
+      expect(nicify(circular)).toBe(deindent`
+        {
+          "a": 1,
+          "self": Ref<value>,
+        }`
+      );
+    });
+  });
+
+  describe("configuration options", () => {
+    test("maxDepth", () => {
+      const deep = { a: { b: { c: { d: { e: 1 } } } } };
+      expect(nicify(deep, { maxDepth: 2 })).toBe('{ "a": { "b": { ... } } }');
+    });
+
+    test("lineIndent", () => {
+      expect(nicify({ a: 1, b: 2 }, { lineIndent: "    " })).toBe(deindent`
+        {
+            "a": 1,
+            "b": 2,
+        }
+      `);
+    });
+
+    test("hideFields", () => {
+      expect(nicify({ a: 1, b: 2, secret: "hidden" }, { hideFields: ["secret"] })).toBe(deindent`
+        {
+          "a": 1,
+          "b": 2,
+          <some fields may have been hidden>,
+        }
+      `);
+    });
+  });
+
+  describe("custom overrides", () => {
+    test("override with custom type", () => {
+      expect(nicify({ type: "special" }, {
+        overrides: ((value: unknown) => {
+          if (typeof value === "object" && value && "type" in value && (value as any).type === "special") {
+            return "SPECIAL";
+          }
+          return null;
+        }) as NicifyOptions["overrides"]
+      })).toBe("SPECIAL");
+    });
+  });
+
+  describe("functions", () => {
+    test("named function", () => {
+      expect(nicify(function namedFunction() {})).toBe("function namedFunction(...) { ... }");
+    });
+
+    test("arrow function", () => {
+      expect(nicify(() => {})).toBe("(...) => { ... }");
+    });
+  });
+
+  describe("Nicifiable interface", () => {
+    test("object implementing Nicifiable", () => {
+      const nicifiable = {
+        value: 42,
+        getNicifiableKeys() {
+          return ["value"];
+        },
+        getNicifiedObjectExtraLines() {
+          return ["// custom comment"];
+        }
+      };
+      expect(nicify(nicifiable)).toBe(deindent`
+        {
+          "value": 42,
+          // custom comment,
+        }
+      `);
+    });
+  });
+
+  describe("unknown types", () => {
+    test("object without prototype", () => {
+      const unknownType = Object.create(null);
+      unknownType.value = "test";
+      expect(nicify(unknownType)).toBe('{ "value": "test" }');
+    });
+  });
+});
diff --git a/packages/stack-shared/src/utils/strings.test.ts b/packages/stack-shared/src/utils/strings.test.ts
deleted file mode 100644
index 307a672e32..0000000000
--- a/packages/stack-shared/src/utils/strings.test.ts
+++ /dev/null
@@ -1,33 +0,0 @@
-import { describe, expect, it } from "vitest";
-import { templateIdentity } from "./strings";
-
-describe("templateIdentity", () => {
-  it("should be equivalent to a regular template string", () => {
-    const adjective = "scientific";
-    const noun = "railgun";
-    expect(templateIdentity`a certain scientific railgun`).toBe("a certain scientific railgun");
-    expect(templateIdentity`a certain ${adjective} railgun`).toBe(`a certain scientific railgun`);
-    expect(templateIdentity`a certain ${adjective} ${noun}`).toBe(`a certain scientific railgun`);
-    expect(templateIdentity`${adjective}${noun}`).toBe(`scientificrailgun`);
-  });
-
-  it("should work with empty strings", () => {
-    expect(templateIdentity``).toBe("");
-    expect(templateIdentity`${""}`).toBe("");
-    expect(templateIdentity`${""}${""}`).toBe("");
-  });
-
-  it("should work with normal arrays", () => {
-    expect(templateIdentity(
-      ["a ", " scientific ", "gun"],
-      "certain", "rail")
-    ).toBe("a certain scientific railgun");
-    expect(templateIdentity(["a"])).toBe("a");
-  });
-
-  it("should throw an error with wrong number of value arguments", () => {
-    expect(() => templateIdentity([])).toThrow();
-    expect(() => templateIdentity(["a", "b"])).toThrow();
-    expect(() => templateIdentity(["a", "b", "c"], "a", "b", "c")).toThrow();
-  });
-});
diff --git a/packages/stack-shared/src/utils/strings.tsx b/packages/stack-shared/src/utils/strings.tsx
index 3480ceb435..ad8508e2c5 100644
--- a/packages/stack-shared/src/utils/strings.tsx
+++ b/packages/stack-shared/src/utils/strings.tsx
@@ -223,7 +223,10 @@ export function deindent(code: string): string;
 export function deindent(strings: TemplateStringsArray | readonly string[], ...values: any[]): string;
 export function deindent(strings: string | readonly string[], ...values: any[]): string {
   if (typeof strings === "string") return deindent([strings]);
-  if (strings.length === 0) return "";
+  return templateIdentity(...deindentTemplate(strings, ...values));
+}
+
+export function deindentTemplate(strings: TemplateStringsArray | readonly string[], ...values: any[]): [string[], ...string[]] {
   if (values.length !== strings.length - 1) throw new StackAssertionError("Invalid number of values; must be one less than strings", { strings, values });
 
   const trimmedStrings = [...strings];
@@ -250,7 +253,7 @@ export function deindent(strings: string | readonly string[], ...values: any[]):
     return `${value}`.replaceAll("\n", `\n${firstLineIndentation}`);
   });
 
-  return templateIdentity(deindentedStrings, ...indentedValues);
+  return [deindentedStrings, ...indentedValues];
 }
 import.meta.vitest?.test("deindent", ({ expect }) => {
   // Test with string input
@@ -261,7 +264,6 @@ import.meta.vitest?.test("deindent", ({ expect }) => {
 
   // Test with empty input
   expect(deindent("")).toBe("");
-  expect(deindent([])).toBe("");
 
   // Test with template literal
   expect(deindent`
@@ -498,12 +500,13 @@ export function nicify(
     keyInParent: null,
     hideFields: [],
   };
-  const nestedNicify = (newValue: unknown, newPath: string, keyInParent: PropertyKey | null) => {
+  const nestedNicify = (newValue: unknown, newPath: string, keyInParent: PropertyKey | null, options: Partial<NicifyOptions> = {}) => {
     return nicify(newValue, {
       ...newOptions,
       path: newPath,
       currentIndent: currentIndent + lineIndent,
       keyInParent,
+      ...options,
     });
   };
 
@@ -515,7 +518,7 @@ export function nicify(
       const isDeindentable = (v: string) => deindent(v) === v && v.includes("\n");
       const wrapInDeindent = (v: string) => deindent`
         deindent\`
-        ${currentIndent + lineIndent}${escapeTemplateLiteral(value).replaceAll("\n", nl + lineIndent)}
+        ${currentIndent + lineIndent}${escapeTemplateLiteral(v).replaceAll("\n", nl + lineIndent)}
         ${currentIndent}\`
       `;
       if (isDeindentable(value)) {
@@ -548,7 +551,7 @@ export function nicify(
         const resValues = value.map((v, i) => nestedNicify(v, `${path}[${i}]`, i));
         resValues.push(...extraLines);
         if (resValues.length !== resValueLength) throw new StackAssertionError("nicify of object: resValues.length !== resValueLength", { value, resValues, resValueLength });
-        const shouldIndent = resValues.length > 1 || resValues.some(x => x.includes("\n"));
+        const shouldIndent = resValues.length > 4 || resValues.some(x => (resValues.length > 1 && x.length > 4) || x.includes("\n"));
         if (shouldIndent) {
           return `[${nl}${resValues.map(x => `${lineIndent}${x},${nl}`).join("")}]`;
         } else {
@@ -556,14 +559,30 @@ export function nicify(
         }
       }
       if (value instanceof URL) {
-        return `URL(${nicify(value.toString())})`;
+        return `URL(${nestedNicify(value.toString(), `${path}.toString()`, null)})`;
       }
       if (ArrayBuffer.isView(value)) {
         return `${value.constructor.name}([${value.toString()}])`;
       }
+      if (value instanceof Error) {
+        let stack = value.stack ?? "";
+        const toString = value.toString();
+        if (!stack.startsWith(toString)) stack = `${toString}\n${stack}`;  // some browsers don't include the error message in the stack, some do
+        stack = stack.trimEnd();
+        stack = stack.replace(/\n\s+/g, `\n${lineIndent}${lineIndent}`);
+        stack = stack.replace("\n", `\n${lineIndent}Stack:\n`);
+        if (Object.keys(value).length > 0) {
+          stack += `\n${lineIndent}Extra properties: ${nestedNicify(Object.fromEntries(Object.entries(value)), path, null)}`;
+        }
+        if (value.cause) {
+          stack += `\n${lineIndent}Cause:\n${lineIndent}${lineIndent}${nestedNicify(value.cause, path, null, { currentIndent: currentIndent + lineIndent + lineIndent })}`;
+        }
+        stack = stack.replaceAll("\n", `\n${currentIndent}`);
+        return stack;
+      }
 
       const constructorName = [null, Object.prototype].includes(Object.getPrototypeOf(value)) ? null : (nicifiableClassNameOverrides.get(value.constructor) ?? value.constructor.name);
-      const constructorString = constructorName ? `${nicifyPropertyString(constructorName)} ` : "";
+      const constructorString = constructorName ? `${constructorName} ` : "";
 
       const entries = getNicifiableEntries(value).filter(([k]) => !hideFields.includes(k));
       const extraLines = [
@@ -575,7 +594,7 @@ export function nicify(
       if (maxDepth <= 0) return `${constructorString}{ ... }`;
       const resValues = entries.map(([k, v], keyIndex) => {
         const keyNicified = nestedNicify(k, `Object.keys(${path})[${keyIndex}]`, null);
-        const keyInObjectLiteral = typeof k === "string" ? JSON.stringify(k) : `[${keyNicified}]`;
+        const keyInObjectLiteral = typeof k === "string" ? nicifyPropertyString(k) : `[${keyNicified}]`;
         if (typeof v === "function" && v.name === k) {
           return `${keyInObjectLiteral}(...): { ... }`;
         } else {
@@ -600,24 +619,68 @@ export function nicify(
 }
 
 export function replaceAll(input: string, searchValue: string, replaceValue: string): string {
+  if (searchValue === "") throw new StackAssertionError("replaceAll: searchValue is empty");
   return input.split(searchValue).join(replaceValue);
 }
+import.meta.vitest?.test("replaceAll", ({ expect }) => {
+  expect(replaceAll("hello world", "o", "x")).toBe("hellx wxrld");
+  expect(replaceAll("aaa", "a", "b")).toBe("bbb");
+  expect(replaceAll("", "a", "b")).toBe("");
+  expect(replaceAll("abc", "b", "")).toBe("ac");
+  expect(replaceAll("test.test.test", ".", "_")).toBe("test_test_test");
+  expect(replaceAll("a.b*c", ".", "x")).toBe("axb*c");
+  expect(replaceAll("a*b*c", "*", "x")).toBe("axbxc");
+  expect(replaceAll("hello hello", "hello", "hi")).toBe("hi hi");
+});
 
 function nicifyPropertyString(str: string) {
-  if (/^[_a-zA-Z][_a-zA-Z0-9]*$/.test(str)) return str;
   return JSON.stringify(str);
 }
+import.meta.vitest?.test("nicifyPropertyString", ({ expect }) => {
+  // Test valid identifiers
+  expect(nicifyPropertyString("validName")).toBe('"validName"');
+  expect(nicifyPropertyString("_validName")).toBe('"_validName"');
+  expect(nicifyPropertyString("valid123Name")).toBe('"valid123Name"');
+
+  // Test invalid identifiers
+  expect(nicifyPropertyString("123invalid")).toBe('"123invalid"');
+  expect(nicifyPropertyString("invalid-name")).toBe('"invalid-name"');
+  expect(nicifyPropertyString("invalid space")).toBe('"invalid space"');
+  expect(nicifyPropertyString("$invalid")).toBe('"$invalid"');
+  expect(nicifyPropertyString("")).toBe('""');
+
+  // Test with special characters
+  expect(nicifyPropertyString("property!")).toBe('"property!"');
+  expect(nicifyPropertyString("property.name")).toBe('"property.name"');
+
+  // Test with escaped characters
+  expect(nicifyPropertyString("\\")).toBe('"\\\\"');
+  expect(nicifyPropertyString('"')).toBe('"\\""');
+});
 
 function getNicifiableKeys(value: Nicifiable | object) {
   const overridden = ("getNicifiableKeys" in value ? value.getNicifiableKeys?.bind(value) : null)?.();
   if (overridden != null) return overridden;
   const keys = Object.keys(value).sort();
-  if (value instanceof Error) {
-    if (value.cause) keys.unshift("cause");
-    keys.unshift("message", "stack");
-  }
   return unique(keys);
 }
+import.meta.vitest?.test("getNicifiableKeys", ({ expect }) => {
+  // Test regular object
+  expect(getNicifiableKeys({ b: 1, a: 2, c: 3 })).toEqual(["a", "b", "c"]);
+
+  // Test empty object
+  expect(getNicifiableKeys({})).toEqual([]);
+
+  // Test object with custom getNicifiableKeys
+  const customObject = {
+    a: 1,
+    b: 2,
+    getNicifiableKeys() {
+      return ["customKey1", "customKey2"];
+    }
+  };
+  expect(getNicifiableKeys(customObject)).toEqual(["customKey1", "customKey2"]);
+});
 
 function getNicifiableEntries(value: Nicifiable | object): [PropertyKey, unknown][] {
   const recordLikes = [Headers];