diff --git a/README.md b/README.md
index 480b945..d5ce589 100644
--- a/README.md
+++ b/README.md
@@ -1 +1,204 @@
 # super-sources [![test](https://github.com/WiseLibs/super-sources/actions/workflows/test.yml/badge.svg)](https://github.com/WiseLibs/super-sources/actions/workflows/test.yml)
+
+This package provides classes for representing pieces of source code, and allows you to print beautiful errors/warnings that display the referenced pieces of source code. Unicode is supported, including the [Supplementary Multilingual Plane](https://en.wikipedia.org/wiki/Plane_(Unicode)#Supplementary_Multilingual_Plane).
+
+## Installation
+
+```
+npm install super-sources
+```
+
+> Requires Node.js v14.x.x or later.
+
+## Usage
+
+```js
+const { File, SourceError } = require('super-sources');
+
+const file = new File('example.txt', 'this is a simple file.\nhello worl!\n');
+const source = file.at(29, 4); // offset 29, length 4
+
+const error = SourceError.build()
+	.error('Misspelling detected')
+	.source(source, 'here')
+	.note('expected: "world"')
+	.note(`received: "${source.string()}"`)
+	.done();
+
+assert(error instanceof Error);
+assert(error instanceof SourceError);
+
+console.log(error.print({ colors: false }));
+```
+
+Result:
+
+```
+Error: Misspelling detected
+ --> example.txt
+  |
+2 |   hello worl!
+  |         ^^^^
+  * expected: "world"
+  * received: "worl"
+```
+
+# API
+
+## new File(*filename*, *content*)
+
+Creates an object that represents a source file.
+
+```js
+const fs = require('fs');
+
+const filename = 'example.txt';
+const content = fs.readFileSync(filename, 'utf8');
+const file = new File(filename, content);
+```
+
+### file.at(*offset*, [*length*]) -> *Source*
+
+Creates a [`Source`](#new-sourcefile-start-end) object, which represents a slice of the source file. The length defaults to `1`.
+
+```js
+const source = file.at(0);
+```
+
+### file.lineNumberAt(*offset*) -> *number*
+
+Returns the line number at the given offset. The first line is `1`.
+
+```js
+const lineNumber = file.lineNumberAt(0);
+
+assert(lineNumber === 1);
+```
+
+### File properties
+
+- `file.filename`: The filename that was passed to the `File` constructor.
+- `file.content`: The content string that was passed to the `File` constructor.
+
+## new Source(*file*, *start*, *end*)
+
+Creates an object that represents a slice of the given [`File`](#new-filefilename-content). The length of the slice (`end - start`) must be at least `1`.
+
+```js
+const fs = require('fs');
+
+const filename = 'example.txt';
+const content = fs.readFileSync(filename, 'utf8');
+const file = new File(filename, content);
+const source = new Source(file, 0, 1);
+```
+
+### source.to(*otherSource*) -> *Source*
+
+Creates a [`Source`](#new-sourcefile-start-end) object that spans the range from this source to the given source. A negative or zero-length range will result in a [`RangeError`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RangeError). Also, both sources must be from the same file.
+
+```js
+const source1 = new Source(file, 0, 5);
+const source2 = new Source(file, 3, 8);
+const result = source1.to(source2);
+
+assert(result.start === 0);
+assert(result.end === 8);
+```
+
+### source.string() -> *string*
+
+Returns the original source string represented by this object.
+
+```js
+const file = new File('example.txt', 'abcdefg');
+const source = new Source(2, 4);
+
+assert(source.string() === 'cd');
+```
+
+### source.error(*message*, [*helperText*]) -> *ErrorBuilder*
+
+Shorthand for `SourceError.build().error(message).source(source, helperText)`. See the [`ErrorBuilder`](#class-errorbuilder) class for more details.
+
+```js
+source.error('Invalid expression').throw();
+```
+
+### source.warning(*message*, [*helperText*]) -> *ErrorBuilder*
+
+Shorthand for `SourceError.build().warning(message).source(source, helperText)`. See the [`ErrorBuilder`](#class-errorbuilder) class for more details.
+
+```js
+console.warn(source.warning('Invalid expression').done().print());
+```
+
+### Source properties
+
+- `source.file`: The [`File`](#new-filefilename-content) that this source came from.
+- `source.start`: The offset where this source slice starts (inclusive).
+- `source.end`: The offset where this source slice ends (exclusive).
+
+## class SourceError
+
+A subclass of [`Error`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error/Error) that can reference [`Source`](#new-sourcefile-start-end) objects, and is capable of printing beautiful error messages containing the source code.
+
+Instead of constructing them manually, you can use the static `SourceError.build()` method to conveniently create a new [`ErrorBuilder`](#class-errorbuilder).
+
+```js
+const error = SourceError.build()
+	.error('Misspelling detected')
+	.source(source, 'here')
+	.note('expected: "world"')
+	.note(`received: "${source.string()}"`)
+	.done();
+```
+
+### error.print([*options*]) -> *string*
+
+Returns a string containing a beautifully formatted error message, containing any source code that this error references.
+
+The following options are supported:
+
+- `colors` (boolean)
+	* Whether or not the output should be colored (by [ANSI escape codes](https://en.wikipedia.org/wiki/ANSI_escape_code)). Default: `true`.
+- `filenames` (boolean)
+	* Whether or not the output should contain the names of the referenced source files. Default: `true`.
+- `lineNumbers` (boolean)
+	* Whether or not the output should contain the line numbers of the referenced source code. Default: `true`.
+- `positions` (boolean)
+	* Whether or not the output should highlight the exact positions of the referenced source code. Default: `true`.
+- `maxLines` (number)
+	* The maximum number of source lines to display (per source snippet) before lines are omitted to save space.
+
+## class ErrorBuilder
+
+A convenient builder class for making customized [`SourceError`](#class-sourceerror) objects.
+
+### builder.error(*message*) -> *this*
+
+Adds an error message to the [`SourceError`](#class-sourceerror) being built. A single [`SourceError`](#class-sourceerror) can contain multiple error messages.
+
+### builder.warning(*message*) -> *this*
+
+Adds a warning message to the [`SourceError`](#class-sourceerror) being built. A single [`SourceError`](#class-sourceerror) can contain multiple warning messages.
+
+### builder.source(*source*, [*helperText*]) -> *this*
+
+Adds a [`Source`](#new-sourcefile-start-end) object to the [`SourceError`](#class-sourceerror) being built. Any number of sources can be added. The added source will be associated with the most recent `.error()` or `.warning()` that was added.
+
+### builder.note(*message*) -> *this*
+
+Adds a note to the [`SourceError`](#class-sourceerror) being built. Any number of notes can be added. The note will be associated with the most recent `.source()` that was added.
+
+### builder.done() -> *SourceError*
+
+Returns a [`SourceError`](#class-sourceerror) containing all errors, warnings, sources, and notes that were added to this [`ErrorBuilder`](#class-errorbuilder).
+
+### builder.throw() -> *throw SourceError*
+
+This is the same as `builder.done()`, but the resulting [`SourceError`](#class-sourceerror) will be immediately thrown.
+
+## License
+
+[MIT](https://github.com/WiseLibs/super-sources/blob/master/LICENSE)
diff --git a/package.json b/package.json
index 7fd2158..51d8ef3 100644
--- a/package.json
+++ b/package.json
@@ -1,7 +1,7 @@
 {
   "name": "super-sources",
   "version": "1.0.0",
-  "description": "Beautiful errors for any source code",
+  "description": "Beautiful error printing for any source code",
   "author": "Joshua Wise <joshuathomaswise@gmail.com>",
   "homepage": "https://github.com/WiseLibs/super-sources#readme",
   "repository": {