@@ -0,0 +1,15 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Pest\Browser\Exceptions;
+
+use RuntimeException;
+
+/**
+ * @internal
+ */
+final class FileNotReadableException extends RuntimeException
+{
+    //
+}
@@ -0,0 +1,15 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Pest\Browser\Exceptions;
+
+use RuntimeException;
+
+/**
+ * @internal
+ */
+final class FileTooLargeException extends RuntimeException
+{
+    //
+}
@@ -6,6 +6,7 @@
 
 use Generator;
 use Pest\Browser\Playwright\Concerns\InteractsWithPlaywright;
+use Pest\Browser\Support\FilePayload;
 use Pest\Browser\Support\Selector;
 use RuntimeException;
 
@@ -651,10 +652,13 @@ public function tap(?array $options = null): void
 
     /**
      * Set input files for a file input element.
+     *
+     * The file is sent by value rather than by path, so that uploads keep
+     * working when the Playwright server is not collocated with the client.
      */
     public function setInputFiles(string $path): void
     {
-        $params = ['localPaths' => [$path]];
+        $params = ['payloads' => [FilePayload::fromPath($path)->toArray()]];
         $response = $this->sendMessage('setInputFiles', $params);
 
         $this->processVoidResponse($response);
 
@@ -0,0 +1,106 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Pest\Browser\Support;
+
+use Pest\Browser\Exceptions\FileNotReadableException;
+use Pest\Browser\Exceptions\FileTooLargeException;
+use Symfony\Component\Mime\MimeTypes;
+
+/**
+ * A file to be uploaded, expressed as an inline Playwright payload.
+ *
+ * Playwright refuses `localPaths` whenever the client is not collocated with
+ * the server, so files are sent by value instead of by path. This keeps
+ * uploads working against a remote `playwright run-server`, and behaves
+ * identically when the server is local.
+ *
+ * @internal
+ */
+final readonly class FilePayload
+{
+    /**
+     * The largest buffer Playwright accepts for an inline payload.
+     */
+    private const int MAX_SIZE_IN_BYTES = 50 * 1024 * 1024;
+
+    /**
+     * The MIME type used when the extension cannot be mapped to a known type.
+     */
+    private const string FALLBACK_MIME_TYPE = 'application/octet-stream';
+
+    /**
+     * Creates a new file payload instance.
+     */
+    private function __construct(
+        private string $name,
+        private string $mimeType,
+        private string $contents,
+    ) {
+        //
+    }
+
+    /**
+     * Create a payload from the file at the given path.
+     */
+    public static function fromPath(string $path): self
+    {
+        if (! is_file($path) || ! is_readable($path)) {
+            throw new FileNotReadableException("The file [{$path}] does not exist or is not readable.");
+        }
+
+        $size = filesize($path);
+
+        if ($size === false) {
+            throw new FileNotReadableException("The size of the file [{$path}] could not be determined.");
+        }
+
+        if ($size > self::MAX_SIZE_IN_BYTES) {
+            throw new FileTooLargeException(
+                "The file [{$path}] exceeds the maximum upload size of 50 MB supported by Playwright."
+            );
+        }
+
+        $contents = file_get_contents($path);
+
+        if ($contents === false) {
+            throw new FileNotReadableException("The file [{$path}] could not be read.");
+        }
+
+        return new self(basename($path), self::guessMimeType($path), $contents);
+    }
+
+    /**
+     * Return the payload in the shape expected by the Playwright protocol.
+     *
+     * The `buffer` field is typed as binary by the protocol, which is
+     * base64 over the JSON channel.
+     *
+     * @return array{name: string, mimeType: string, buffer: string}
+     */
+    public function toArray(): array
+    {
+        return [
+            'name' => $this->name,
+            'mimeType' => $this->mimeType,
+            'buffer' => base64_encode($this->contents),
+        ];
+    }
+
+    /**
+     * Guess the MIME type of the file from its extension.
+     */
+    private static function guessMimeType(string $path): string
+    {
+        $extension = pathinfo($path, PATHINFO_EXTENSION);
+
+        if ($extension === '') {
+            return self::FALLBACK_MIME_TYPE;
+        }
+
+        $mimeTypes = (new MimeTypes())->getMimeTypes($extension);
+
+        return $mimeTypes[0] ?? self::FALLBACK_MIME_TYPE;
+    }
+}
@@ -0,0 +1,121 @@
+<?php
+
+declare(strict_types=1);
+
+use Pest\Browser\Exceptions\FileNotReadableException;
+use Pest\Browser\Exceptions\FileTooLargeException;
+use Pest\Browser\Support\FilePayload;
+
+/**
+ * Create a temporary file with the given contents and extension.
+ */
+function temporaryFile(string $contents, string $extension = ''): string
+{
+    $path = tempnam(sys_get_temp_dir(), 'pest_payload');
+
+    if ($extension !== '') {
+        unlink($path);
+        $path .= '.'.$extension;
+    }
+
+    file_put_contents($path, $contents);
+
+    return $path;
+}
+
+test('sends the file by value instead of by path', function (): void {
+    $path = temporaryFile('hello world', 'txt');
+
+    $payload = FilePayload::fromPath($path)->toArray();
+
+    expect($payload)->toHaveKeys(['name', 'mimeType', 'buffer'])
+        ->and($payload)->not->toHaveKey('localPaths')
+        ->and($payload['buffer'])->not->toBe($path);
+
+    unlink($path);
+});
+
+test('encodes the buffer as base64', function (): void {
+    $path = temporaryFile('hello world', 'txt');
+
+    $payload = FilePayload::fromPath($path)->toArray();
+
+    expect($payload['buffer'])->toBe(base64_encode('hello world'))
+        ->and(base64_decode($payload['buffer'], true))->toBe('hello world');
+
+    unlink($path);
+});
+
+test('preserves binary contents without corruption', function (): void {
+    $contents = '';
+    for ($byte = 0; $byte < 256; $byte++) {
+        $contents .= pack('C', $byte);
+    }
+    $contents .= "\x00\xC3\x28\xFF\xFE invalid utf-8 \r\n ";
+
+    $path = temporaryFile($contents, 'bin');
+
+    $payload = FilePayload::fromPath($path)->toArray();
+    $decoded = (string) base64_decode($payload['buffer'], true);
+
+    expect(hash('sha256', $decoded))->toBe(hash('sha256', $contents))
+        ->and($decoded)->toBe($contents);
+
+    unlink($path);
+});
+
+test('uses the file name rather than the full path', function (): void {
+    $path = temporaryFile('contents', 'txt');
+
+    expect(FilePayload::fromPath($path)->toArray()['name'])->toBe(basename($path));
+
+    unlink($path);
+});
+
+test('guesses the mime type from the extension', function (): void {
+    $path = temporaryFile('{}', 'json');
+
+    expect(FilePayload::fromPath($path)->toArray()['mimeType'])->toBe('application/json');
+
+    unlink($path);
+});
+
+test('falls back to a generic mime type for unknown extensions', function (): void {
+    $path = temporaryFile('contents', 'unknownext');
+
+    expect(FilePayload::fromPath($path)->toArray()['mimeType'])->toBe('application/octet-stream');
+
+    unlink($path);
+});
+
+test('falls back to a generic mime type when there is no extension', function (): void {
+    $path = temporaryFile('contents');
+
+    expect(FilePayload::fromPath($path)->toArray()['mimeType'])->toBe('application/octet-stream');
+
+    unlink($path);
+});
+
+test('fails when the file does not exist', function (): void {
+    FilePayload::fromPath('/this/path/does/not/exist.txt');
+})->throws(FileNotReadableException::class);
+
+test('fails when the path is a directory', function (): void {
+    FilePayload::fromPath(sys_get_temp_dir());
+})->throws(FileNotReadableException::class);
+
+test('fails when the file exceeds the playwright payload limit', function (): void {
+    $path = temporaryFile('');
+
+    $handle = fopen($path, 'wb');
+    fseek($handle, 50 * 1024 * 1024);
+    fwrite($handle, 'x');
+    fclose($handle);
+
+    try {
+        expect(fn (): array => FilePayload::fromPath($path)->toArray())
+            ->toThrow(FileTooLargeException::class);
+    } finally {
+        unlink($path);
+    }
+});