diff --git a/_test/fixture/a/b/c/findme.md b/_test/fixture/fs/a/b/c/findme.md
similarity index 100%
rename from _test/fixture/a/b/c/findme.md
rename to _test/fixture/fs/a/b/c/findme.md
diff --git a/_test/fixture/a/b/c/findme.ts b/_test/fixture/fs/a/b/c/findme.ts
similarity index 100%
rename from _test/fixture/a/b/c/findme.ts
rename to _test/fixture/fs/a/b/c/findme.ts
diff --git a/_test/fixture/a/findme.md b/_test/fixture/fs/a/findme.md
similarity index 100%
rename from _test/fixture/a/findme.md
rename to _test/fixture/fs/a/findme.md
diff --git a/_test/fixture/a/findme.ts b/_test/fixture/fs/a/findme.ts
similarity index 100%
rename from _test/fixture/a/findme.ts
rename to _test/fixture/fs/a/findme.ts
diff --git a/_test/fixture/json/invalid.json b/_test/fixture/json/invalid.json
new file mode 100644
index 00000000..81750b96
--- /dev/null
+++ b/_test/fixture/json/invalid.json
@@ -0,0 +1 @@
+{
\ No newline at end of file
diff --git a/_test/fixture/json/valid.json b/_test/fixture/json/valid.json
new file mode 100644
index 00000000..c8c4105e
--- /dev/null
+++ b/_test/fixture/json/valid.json
@@ -0,0 +1,3 @@
+{
+  "foo": "bar"
+}
diff --git a/_test/fixture/ts/invalid.ts b/_test/fixture/ts/invalid.ts
new file mode 100644
index 00000000..d2c911f8
--- /dev/null
+++ b/_test/fixture/ts/invalid.ts
@@ -0,0 +1,3 @@
+// deno-lint-ignore ban-ts-comment
+// @ts-expect-error
+invalid;
diff --git a/_test/fixture/ts/invalidTypes.ts b/_test/fixture/ts/invalidTypes.ts
new file mode 100644
index 00000000..d093c650
--- /dev/null
+++ b/_test/fixture/ts/invalidTypes.ts
@@ -0,0 +1,2 @@
+const foo: number = "Hello";
+console.log(foo);
diff --git a/_test/fixture/ts/throws.ts b/_test/fixture/ts/throws.ts
new file mode 100644
index 00000000..0e01f3a9
--- /dev/null
+++ b/_test/fixture/ts/throws.ts
@@ -0,0 +1 @@
+throw new Error("");
diff --git a/_test/fixture/ts/valid.ts b/_test/fixture/ts/valid.ts
new file mode 100644
index 00000000..7f944f48
--- /dev/null
+++ b/_test/fixture/ts/valid.ts
@@ -0,0 +1,3 @@
+// deno-lint-ignore no-inferrable-types
+const foo: string = "Hello";
+console.log(foo);
diff --git a/fs/fileHandler.ts b/fs/fileHandler.ts
new file mode 100644
index 00000000..2c6fdc0a
--- /dev/null
+++ b/fs/fileHandler.ts
@@ -0,0 +1,115 @@
+export type FileHandler = {
+  read: (filePath: string) => unknown | Promise<unknown>;
+
+  // deno-lint-ignore no-explicit-any
+  write: (filePath: string, data: any) => Promise<void>;
+};
+
+/** A helper class for handling files by extensions. */
+export abstract class FileExtensionHandler<Ext extends string = string> {
+  extensions: Ext[];
+
+  constructor(extensions?: Ext[]) {
+    this.extensions = extensions ?? [];
+  }
+
+  /** @returns `true` if the file path ends with one of the extensions. */
+  validateExtension(filePath: string): filePath is `${string}${Ext}` {
+    if (!this.extensions.length) return true;
+
+    return this.extensions.some((ext) => filePath.endsWith(ext));
+  }
+
+  /** @throws {InvalidExtensionError} if the file path does not end with one of the extensions. */
+  assertValidExtension(
+    filePath: string,
+  ): asserts filePath is `${string}${Ext}` {
+    if (!this.validateExtension(filePath)) {
+      throw new InvalidExtensionError(filePath, this.extensions);
+    }
+  }
+}
+
+export type Evaluable = {
+  evaluate: (filePath: string) => unknown | Promise<unknown>;
+};
+
+export class InvalidExtensionError extends TypeError {
+  constructor(filePath: string, extensions: string[]) {
+    const extensionsString = extensions
+      .map((e) => JSON.stringify(e))
+      .join(", ");
+
+    super(
+      "File path does not end with one of the extensions:\n" +
+        `  path: ${filePath}\n` +
+        `  extensions: ${extensionsString}`,
+    );
+    this.name = "InvalidExtensionError";
+  }
+}
+
+export type FileHandlerMethodOptions = {
+  /** If `true`, the method will not validate the file extension. */
+  force?: boolean;
+};
+
+/** A sample implementation with `FileHandler` and `FileExtensionHandler` which
+ * can serve as a base class for handlers of UTF8-encoded files.
+ *
+ * @example
+ * const handler = new PlainTextFileHandler();
+ *
+ * await handler.read("./license"); // "BSD Zero Clause License ..."
+ * await handler.write("./readme.md", "# Hello, world!");
+ *
+ * @example
+ * const handler = new PlainTextFileHandler([".txt"]);
+ *
+ * handler.validateExtension("foo.txt"); // true
+ * handler.validateExtension("foo.md"); // false
+ * await handler.read("./readme.md"); // throws InvalidExtensionError
+ *
+ * @example
+ * // TypeScript constraint: you must use `:` to explicitly specify
+ * // the type for assertions to work
+ * const handler: PlainTextFileHandler<".md"> = new PlainTextFileHandler([".md"]);
+ *
+ * handler.assertValidExtension("foo.txt"); // throws InvalidExtensionError
+ *
+ * @example
+ * import { cmd } from "../cli/utils.ts";
+ *
+ * class TypeScriptFileHandler extends PlainTextFileHandler<"ts">
+ *   implements FileHandler, Evaluable {
+ *   constructor() {
+ *     super([".ts"]);
+ *   }
+ *
+ *   async evaluate(filePath: string) {
+ *     const code = await this.read(filePath);
+ *
+ *     return await cmd(
+ *       ["deno", "eval", "-q", "--check", "--ext=ts", code]
+ *     );
+ *   }
+ * } */
+export class PlainTextFileHandler<Ext extends string = string>
+  extends FileExtensionHandler<Ext>
+  implements FileHandler {
+  constructor(extensions?: Ext[]) {
+    super(extensions);
+  }
+
+  async read(filePath: string, opts?: FileHandlerMethodOptions) {
+    opts?.force || this.assertValidExtension(filePath);
+
+    return await Deno.readTextFile(filePath);
+  }
+
+  async write(filePath: string, data: string, opts?: FileHandlerMethodOptions) {
+    opts?.force || this.assertValidExtension(filePath);
+
+    await Deno.writeTextFile(filePath, data);
+  }
+}
diff --git a/fs/findNearestFile.test.ts b/fs/findNearestFile.test.ts
index 7e9bf286..88554eb7 100644
--- a/fs/findNearestFile.test.ts
+++ b/fs/findNearestFile.test.ts
@@ -3,7 +3,7 @@ import { assertEquals, assertRejects, describe, it } from "../_deps/testing.ts";
 import { FIXTURE_DIR } from "../_constants.ts";
 import { findNearestFile } from "./findNearestFile.ts";
 
-const A_DIR = resolve(FIXTURE_DIR, "a");
+const A_DIR = resolve(FIXTURE_DIR, "fs", "a");
 const B_DIR = resolve(A_DIR, "b");
 const C_DIR = resolve(B_DIR, "c");
 
diff --git a/fs/glob.test.ts b/fs/glob.test.ts
index 97bd2bfb..b3d3f2db 100644
--- a/fs/glob.test.ts
+++ b/fs/glob.test.ts
@@ -3,9 +3,9 @@ import { assertArrayIncludes, describe, it } from "../_deps/testing.ts";
 import { glob } from "./glob.ts";
 import { FIXTURE_DIR } from "../_constants.ts";
 
-const GLOB = resolve(FIXTURE_DIR, "**", "*.ts");
+const GLOB = resolve(FIXTURE_DIR, "fs", "**", "*.ts");
 
-const A_DIR = resolve(FIXTURE_DIR, "a");
+const A_DIR = resolve(FIXTURE_DIR, "fs", "a");
 const C_DIR = resolve(A_DIR, "b", "c");
 
 const A_FILE = resolve(A_DIR, "findme.ts");
diff --git a/fs/globImport.test.ts b/fs/globImport.test.ts
index 92ecd000..f9c3826f 100644
--- a/fs/globImport.test.ts
+++ b/fs/globImport.test.ts
@@ -10,9 +10,9 @@ import {
 import { FileHandlerError, globImport } from "./globImport.ts";
 import { FIXTURE_DIR } from "../_constants.ts";
 
-const globPattern = resolve(FIXTURE_DIR, "**", "*.ts");
+const globPattern = resolve(FIXTURE_DIR, "fs", "**", "*.ts");
 
-const A_DIR = resolve(FIXTURE_DIR, "a");
+const A_DIR = resolve(FIXTURE_DIR, "fs", "a");
 const C_DIR = resolve(A_DIR, "b", "c");
 
 const A_MD = toFileUrl(resolve(A_DIR, "findme.md")).href;
@@ -52,7 +52,7 @@ describe("fs.globImport", () => {
   it("can handle files by extension", async () =>
     assertEquals(
       await globImport(
-        resolve(FIXTURE_DIR, "a", "**", "*.*"),
+        resolve(A_DIR, "**", "*.*"),
         {
           eager: true,
           fileHandler: {
diff --git a/json/fileHandler.test.ts b/json/fileHandler.test.ts
new file mode 100644
index 00000000..a85445e4
--- /dev/null
+++ b/json/fileHandler.test.ts
@@ -0,0 +1,25 @@
+import { FIXTURE_DIR } from "../_constants.ts";
+import { resolve } from "../_deps/path.ts";
+import { assertEquals, assertRejects, describe, it } from "../_deps/testing.ts";
+import { JsonFileHandler } from "./fileHandler.ts";
+
+const valid = resolve(FIXTURE_DIR, "json", "valid.json");
+const invalid = resolve(FIXTURE_DIR, "json", "invalid.json");
+
+describe(".read()", () => {
+  it("returns stdout", async () =>
+    assertEquals(
+      await new JsonFileHandler().read(valid),
+      { foo: "bar" },
+    ));
+
+  it("throws on invalid file content", async () =>
+    void await assertRejects(
+      () => new JsonFileHandler().read(invalid),
+      SyntaxError,
+    ));
+});
+
+describe(".write()", () => {
+  // TODO: stub Deno.writeTextFile()
+});
diff --git a/json/fileHandler.ts b/json/fileHandler.ts
new file mode 100644
index 00000000..762b8833
--- /dev/null
+++ b/json/fileHandler.ts
@@ -0,0 +1,74 @@
+import { FileExtensionHandler, FileHandler } from "../fs/fileHandler.ts";
+import { JsonValue } from "./types.ts";
+
+export type JsonReadOptions<ReviverResult = JsonValue> = {
+  // deno-lint-ignore no-explicit-any
+  reviver?: ((this: any, key: string, value: any) => ReviverResult) | undefined;
+};
+
+// deno-lint-ignore no-explicit-any
+export type JsonWriteOptions<ReplacerResult = any> = {
+  // deno-lint-ignore no-explicit-any
+  replacer?: (this: any, key: string, value: any) => ReplacerResult;
+  space?: string | number;
+};
+
+/**
+ * @example
+ * const handler = new JsonFileHandler();
+ *
+ * await handler.write("foo.json", { foo: "bar" });
+ * // foo.json: '{\n  "foo":"bar"\n}' (2 space indent by default)
+ *
+ * await handler.read("foo.json"); // { foo: "bar" }
+ * await handler.read("foo.yaml"); // throws InvalidExtensionError
+ *
+ * @example
+ * const handler = new JsonFileHandler({ write: { space: 0 } });
+ * await handler.write("foo.json", { foo: "bar" });
+ * // foo.json: '{"foo":"bar"}' (no spaces)
+ */
+export class JsonFileHandler extends FileExtensionHandler
+  implements FileHandler {
+  constructor(
+    public readonly options: {
+      read?: JsonReadOptions;
+      write?: JsonWriteOptions;
+    } = {},
+  ) {
+    super([".json"]);
+  }
+
+  async read(filePath: string): Promise<JsonValue>;
+  async read<T = JsonValue>(
+    filePath: string,
+    opts?: JsonReadOptions<T>,
+  ): Promise<JsonValue>;
+  async read(filePath: string, opts?: JsonReadOptions) {
+    const { reviver } = opts ?? this.options.read ?? {};
+
+    this.assertValidExtension(filePath);
+    const raw = await Deno.readTextFile(filePath);
+
+    return JSON.parse(raw, reviver);
+  }
+
+  async write(filePath: string, data: JsonValue): Promise<void>;
+  // deno-lint-ignore no-explicit-any
+  async write<ReplacerResult = any>(
+    filePath: string,
+    data: JsonValue,
+    opts: JsonWriteOptions<ReplacerResult>,
+  ): Promise<void>;
+  async write(
+    filePath: string,
+    data: JsonValue,
+    opts: JsonWriteOptions = {},
+  ): Promise<void> {
+    const { replacer, space = 2 } = opts ?? this.options.write ?? {};
+
+    this.assertValidExtension(filePath);
+
+    await Deno.writeTextFile(filePath, JSON.stringify(data, replacer, space));
+  }
+}
diff --git a/json/mod.ts b/json/mod.ts
new file mode 100644
index 00000000..b47e50ed
--- /dev/null
+++ b/json/mod.ts
@@ -0,0 +1,2 @@
+export * from "./types.ts";
+export * from "./utils.ts";
diff --git a/types/json.ts b/json/types.ts
similarity index 100%
rename from types/json.ts
rename to json/types.ts
diff --git a/json/utils.ts b/json/utils.ts
new file mode 100644
index 00000000..551adfac
--- /dev/null
+++ b/json/utils.ts
@@ -0,0 +1 @@
+export * from "./fileHandler.ts";
diff --git a/readme.md b/readme.md
index cd297786..d9c516a7 100644
--- a/readme.md
+++ b/readme.md
@@ -12,13 +12,13 @@ Utility functions, classes, types, and scripts in uncompiled TS, for Deno.
   - [`script/makeReleaseNotes`](#scriptmakereleasenotes)
 - [`graph`](#graph)
 - [`io`](#io)
+- [`json`](#json)
 - [`md`](#md)
   - [`script/evalCodeBlocks`](#scriptevalcodeblocks)
 - [`object`](#object)
 - [`path`](#path)
 - [`string`](#string)
 - [`ts`](#ts)
-- [`types`](#types)
 
 ## `array`
 
@@ -156,6 +156,24 @@ clipboard.copy("foo");
 clipboard.paste(); // "foo"
 ```
 
+## `json`
+
+Utility types.
+
+```ts
+import {
+  JsonArray,
+  JsonObject,
+  JsonPrimitive,
+  JsonValue,
+} from "https://deno.land/x/handy/json/types.ts";
+
+const a: JsonPrimitive = "some string"; // or number, boolean, null
+const b: JsonArray = [1, ["2", true], { a: null }];
+const c: JsonObject = { a: 1, b: ["2", true], d: { e: null } };
+// JsonValue = any of the above
+```
+
 ## `md`
 
 Markdown-related utilities.
@@ -242,21 +260,3 @@ import { evaluate } from "https://deno.land/x/handy/ts/utils.ts";
 await evaluate("console.log('Hello!')")
   .then((res) => res.stdout); // "Hello!"
 ```
-
-## `types`
-
-Utility types.
-
-```ts
-import {
-  JsonArray,
-  JsonObject,
-  JsonPrimitive,
-  JsonValue,
-} from "https://deno.land/x/handy/types/json.ts";
-
-const a: JsonPrimitive = "some string"; // or number, boolean, null
-const b: JsonArray = [1, ["2", true], { a: null }];
-const c: JsonObject = { a: 1, b: ["2", true], d: { e: null } };
-// JsonValue = any of the above
-```
diff --git a/ts/fileHandler.test.ts b/ts/fileHandler.test.ts
new file mode 100644
index 00000000..2ba9db81
--- /dev/null
+++ b/ts/fileHandler.test.ts
@@ -0,0 +1,44 @@
+import { FIXTURE_DIR } from "../_constants.ts";
+import { resolve } from "../_deps/path.ts";
+import { assertEquals, assertRejects, describe, it } from "../_deps/testing.ts";
+import { CmdError } from "../cli/cmd.ts";
+import { TypeScriptFileHandler } from "./fileHandler.ts";
+
+const valid = resolve(FIXTURE_DIR, "ts", "valid.ts");
+const invalid = resolve(FIXTURE_DIR, "ts", "invalid.ts");
+const invalidTypes = resolve(FIXTURE_DIR, "ts", "invalidTypes.ts");
+const throws = resolve(FIXTURE_DIR, "ts", "throws.ts");
+
+describe("TypeScriptFileHandler.prototype.evaluate()", () => {
+  it("returns stdout", async () =>
+    assertEquals(
+      await new TypeScriptFileHandler().evaluate(valid),
+      "Hello",
+    ));
+
+  it("throws when code throws", async () =>
+    void await assertRejects(
+      () => new TypeScriptFileHandler().evaluate(throws),
+      CmdError,
+    ));
+
+  it("throws on invalid input", async () =>
+    void await assertRejects(
+      () => new TypeScriptFileHandler().evaluate(invalid),
+      CmdError,
+    ));
+
+  describe("type checking", () => {
+    it("is enabled by default", async () =>
+      void await assertRejects(
+        () => new TypeScriptFileHandler().evaluate(invalidTypes),
+      ));
+
+    it("can be disabled", async () =>
+      void assertEquals(
+        await new TypeScriptFileHandler({ typeCheck: false })
+          .evaluate(invalidTypes),
+        "Hello",
+      ));
+  });
+});
diff --git a/ts/fileHandler.ts b/ts/fileHandler.ts
new file mode 100644
index 00000000..b4bff2bf
--- /dev/null
+++ b/ts/fileHandler.ts
@@ -0,0 +1,30 @@
+import {
+  Evaluable,
+  FileHandler,
+  FileHandlerMethodOptions,
+  PlainTextFileHandler,
+} from "../fs/fileHandler.ts";
+import { evaluate } from "./evaluate.ts";
+
+/** Type checking is enabled by default. */
+export class TypeScriptFileHandler extends PlainTextFileHandler<".ts">
+  implements FileHandler, Evaluable {
+  public readonly typeCheck: boolean;
+
+  constructor(opts?: { typeCheck: boolean }) {
+    super([".ts"]);
+
+    const { typeCheck = true } = opts ?? {};
+
+    this.typeCheck = typeCheck;
+  }
+
+  async evaluate(
+    filePath: string,
+    opts?: FileHandlerMethodOptions,
+  ) {
+    const code = await this.read(filePath, opts);
+
+    return await evaluate(code, { typeCheck: this.typeCheck });
+  }
+}
diff --git a/ts/utils.ts b/ts/utils.ts
index 1dd8e243..162ccbcb 100644
--- a/ts/utils.ts
+++ b/ts/utils.ts
@@ -1 +1,2 @@
 export * from "./evaluate.ts";
+export * from "./fileHandler.ts";
diff --git a/types/mod.ts b/types/mod.ts
deleted file mode 100644
index 0600fe3a..00000000
--- a/types/mod.ts
+++ /dev/null
@@ -1 +0,0 @@
-export * from "./json.ts";