diff --git a/src/utils/environment.ts b/src/utils/environment.ts
new file mode 100644
index 0000000..2f4e68c
--- /dev/null
+++ b/src/utils/environment.ts
@@ -0,0 +1,134 @@
+import { asString } from "@/utils/string-utils";
+import { EOL } from "node:os";
+
+/**
+ * An object containing environment variables as key-value pairs.
+ */
+export const ENVIRONMENT: Record<string, string> = process.env;
+
+/**
+ * The Windows-style line break character sequence.
+ */
+export const WINDOWS_NEWLINE = "\r\n";
+
+/**
+ * The Unix-style line break character sequence.
+ */
+export const UNIX_NEWLINE = "\n";
+
+/**
+ * The default line break character sequence based on the operating system.
+ */
+export const DEFAULT_NEWLINE = EOL;
+
+/**
+ * Retrieves the environment variable with the specified `name`.
+ *
+ * @param name - The name of the environment variable to retrieve.
+ * @param env - An optional set of the environment variables to search within. Defaults to `process.env`.
+ *
+ * @returns The value of the specified environment variable, if any; otherwise, `undefined`.
+ */
+export function getEnvironmentVariable(name: string, env?: Record<string, string>): string {
+    env ||= ENVIRONMENT;
+
+    const variable = env[name];
+    return variable === undefined ? undefined : asString(variable);
+}
+
+/**
+ * Returns an iterable that yields all environment variables as name/value key-value pairs.
+ *
+ * @param env - An optional set of the environment variables to search within. Defaults to `process.env`.
+ *
+ * @returns An iterable that yields all environment variables as name/value key-value pairs.
+ */
+export function* getAllEnvironmentVariables(env?: Record<string, string>): Iterable<[string, string]> {
+    env ||= ENVIRONMENT;
+
+    for (const [name, variable] of Object.entries(env)) {
+        if (variable === undefined) {
+            continue;
+        }
+
+        yield [name, asString(variable)];
+    }
+}
+
+/**
+ * Updates the value of an environment variable with the specified name.
+ *
+ * @param name - The name of the environment variable to update.
+ * @param value - The new value for the environment variable.
+ * @param env - An optional set of the environment variables to update. Defaults to `process.env`.
+ */
+export function setEnvironmentVariable(name: string, value: unknown, env?: Record<string, string>): void {
+    env ||= ENVIRONMENT;
+
+    if (value === undefined) {
+        delete env[name];
+    } else {
+        env[name] = asString(value);
+    }
+}
+
+/**
+ * Determines whether the current environment is in debug mode.
+ *
+ * @param env - An optional set of the environment variables to check. Defaults to `process.env`.
+ *
+ * @returns `true` if the environment is in debug mode; otherwise, `false`.
+ */
+export function isDebug(env?: Record<string, string>): boolean {
+    // Why in the world is this "1" instead of "true"?
+    // https://docs.github.com/en/actions/learn-github-actions/variables#default-environment-variables
+    return getEnvironmentVariable("RUNNER_DEBUG", env) === "1";
+}
+
+/**
+ * Determines whether the current environment is running on GitHub Actions.
+ *
+ * @param env - An optional set of the environment variables to check. Defaults to `process.env`.
+ *
+ * @returns `true` if the current environment is running on GitHub Actions; otherwise, `false`.
+ */
+export function isGitHubAction(env?: Record<string, string>): boolean {
+    // https://docs.github.com/en/actions/learn-github-actions/variables#default-environment-variables
+    return getEnvironmentVariable("GITHUB_ACTIONS", env) === "true";
+}
+
+/**
+ * Determines whether the specified platform is Windows.
+ *
+ * @param platformName - An optional string that represents the platform to check. If not provided, the current platform will be used as the default.
+ *
+ * @returns `true` if the specified platform is Windows; otherwise, `false`.
+ */
+export function isWindows(platformName?: string): boolean {
+    platformName ??= process.platform;
+    return (platformName as typeof process.platform) === "win32";
+}
+
+/**
+ * Determines whether the current platform is macOS.
+ *
+ * @param platformName - An optional string that represents the platform to check. If not provided, the current platform will be used as the default.
+ *
+ * @returns `true` if the current platform is macOS; otherwise, `false`.
+ */
+export function isMacOs(platformName?: string): boolean {
+    platformName ??= process.platform;
+    return (platformName as typeof process.platform) === "darwin";
+}
+
+/**
+ * Determines whether the current platform is Linux.
+ *
+ * @param platformName - An optional string that represents the platform to check. If not provided, the current platform will be used as the default.
+ *
+ * @returns `true` if the current platform is Linux; otherwise, `false`.
+ */
+export function isLinux(platformName?: string): boolean {
+    platformName ??= process.platform;
+    return (platformName as typeof process.platform) === "linux";
+}
diff --git a/tests/unit/utils/environment.spec.ts b/tests/unit/utils/environment.spec.ts
new file mode 100644
index 0000000..11ba84e
--- /dev/null
+++ b/tests/unit/utils/environment.spec.ts
@@ -0,0 +1,224 @@
+import {
+    getEnvironmentVariable,
+    getAllEnvironmentVariables,
+    setEnvironmentVariable,
+    isDebug,
+    isGitHubAction,
+    isWindows,
+    isMacOs,
+    isLinux,
+} from "@/utils/environment";
+
+const OLD_ENV = { ...process.env };
+
+const OLD_PLATFORM = Object.getOwnPropertyDescriptor(process, "platform");
+
+beforeEach(() => {
+    jest.resetModules();
+});
+
+afterEach(() => {
+    Object.keys(process.env).forEach(key => delete process.env[key]);
+    Object.assign(process.env, OLD_ENV);
+    Object.defineProperty(process, "platform", OLD_PLATFORM);
+});
+
+describe("getEnvironmentVariable", () => {
+    test("gets environment variable", () => {
+        const env = { TEST_VAR: "test" };
+
+        const testVar = getEnvironmentVariable("TEST_VAR", env);
+
+        expect(testVar).toBe("test");
+    });
+
+    test("always returns a string for existing values", () => {
+        const env = { TEST_VAR: 42 as unknown as string };
+
+        const testVar = getEnvironmentVariable("TEST_VAR", env);
+
+        expect(testVar).toBe("42");
+    });
+
+    test("always returns undefined for undefined values", () => {
+        const env = {};
+
+        const testVar = getEnvironmentVariable("TEST_VAR", env);
+
+        expect(testVar).toBeUndefined();
+    });
+
+    test("uses process.env by default", () => {
+        process.env.TEST_VAR = "test";
+
+        const testVar = getEnvironmentVariable("TEST_VAR");
+
+        expect(testVar).toBe("test");
+    });
+});
+
+describe("getAllEnvironmentVariables", () => {
+    test("returns all environment variables as name/value key-value pairs", () => {
+        const env = {
+            VAR1: "value1",
+            VAR2: "value2",
+            VAR3: "value3",
+        };
+
+        const result = Array.from(getAllEnvironmentVariables(env));
+
+        expect(result).toEqual([
+            ["VAR1", "value1"],
+            ["VAR2", "value2"],
+            ["VAR3", "value3"],
+        ]);
+    });
+
+    test("skips variables with undefined value", () => {
+        const env = {
+            VAR1: "value1",
+            VAR2: undefined,
+            VAR3: "value3",
+        };
+
+        const result = Array.from(getAllEnvironmentVariables(env));
+
+        expect(result).toEqual([
+            ["VAR1", "value1"],
+            ["VAR3", "value3"],
+        ]);
+    });
+
+    test("always returns strings for existing values", () => {
+        const env = { TEST_VAR: 42 as unknown as string };
+
+        const result = Array.from(getAllEnvironmentVariables(env));
+
+        expect(result).toEqual([
+            ["TEST_VAR", "42"],
+        ]);
+    });
+
+    test("uses process.env by default", () => {
+        process.env.TEST_VAR = "testValue";
+
+        const result = Array.from(getAllEnvironmentVariables()).find(([name]) => name === "TEST_VAR");
+
+        expect(result).toEqual(["TEST_VAR", "testValue"]);
+    });
+});
+
+describe("setEnvironmentVariable", () => {
+    test("sets environment variable", () => {
+        const env = {};
+
+        setEnvironmentVariable("TEST_VAR", "test", env);
+
+        expect(env["TEST_VAR"]).toBe("test");
+    });
+
+    test("always converts values to strings", () => {
+        const env = {};
+
+        setEnvironmentVariable("TEST_VAR", 42, env);
+
+        expect(env["TEST_VAR"]).toBe("42");
+    });
+
+    test("uses process.env by default", () => {
+        setEnvironmentVariable("TEST_VAR", "test");
+
+        expect(process.env.TEST_VAR).toBe("test");
+    });
+});
+
+describe("isDebug", () => {
+    test("returns true when RUNNER_DEBUG is 1", () => {
+        const env = { RUNNER_DEBUG: "1" };
+
+        expect(isDebug(env)).toBe(true);
+    });
+
+    test("returns false when RUNNER_DEBUG is not 1", () => {
+        const env = { RUNNER_DEBUG: "true" };
+
+        expect(isDebug(env)).toBe(false);
+    });
+
+    test("uses process.env by default", () => {
+        process.env.RUNNER_DEBUG = "1";
+
+        expect(isDebug()).toBe(true);
+    });
+});
+
+describe("isGitHubAction", () => {
+    test("returns true when GITHUB_ACTIONS is 'true'", () => {
+        const env = { GITHUB_ACTIONS: "true" };
+
+        expect(isGitHubAction(env)).toBe(true);
+    });
+
+    test("returns false when GITHUB_ACTIONS is not 'true'", () => {
+        const env = {};
+
+        expect(isGitHubAction(env)).toBe(false);
+    });
+
+    test("uses process.env by default", () => {
+        process.env.GITHUB_ACTIONS = "true";
+
+        expect(isGitHubAction()).toBe(true);
+    });
+});
+
+describe("isWindows", () => {
+    test("returns true when platform is Windows", () => {
+        expect(isWindows("win32")).toBe(true);
+    });
+
+    test("returns false when platform is not Windows", () => {
+        expect(isWindows("darwin")).toBe(false);
+        expect(isWindows("linux")).toBe(false);
+    });
+
+    test("uses process.platform by default", () => {
+        Object.defineProperty(process, "platform", { value: "win32" });
+
+        expect(isWindows()).toBe(true);
+    });
+});
+
+describe("isMacOS", () => {
+    test("returns true when platform is macOS", () => {
+        expect(isMacOs("darwin")).toBe(true);
+    });
+
+    test("returns false when platform is not macOS", () => {
+        expect(isMacOs("win32")).toBe(false);
+        expect(isMacOs("linux")).toBe(false);
+    });
+
+    test("uses process.platform by default", () => {
+        Object.defineProperty(process, "platform", { value: "darwin" });
+
+        expect(isMacOs()).toBe(true);
+    });
+});
+
+describe("isLinux", () => {
+    test("returns true when platform is Linux", () => {
+        expect(isLinux("linux")).toBe(true);
+    });
+
+    test("returns false when platform is not Linux", () => {
+        expect(isLinux("win32")).toBe(false);
+        expect(isLinux("darwin")).toBe(false);
+    });
+
+    test("uses process.platform by default", () => {
+        Object.defineProperty(process, "platform", { value: "linux" });
+
+        expect(isLinux()).toBe(true);
+    });
+});