diff --git a/fixtures/InvalidFile.php b/fixtures/InvalidFile.php
new file mode 100644
index 0000000..a7f2351
--- /dev/null
+++ b/fixtures/InvalidFile.php
@@ -0,0 +1,6 @@
+<?php
+
+interface class
+{
+
+}
diff --git a/fixtures/Symbols.php b/fixtures/Symbols.php
new file mode 100644
index 0000000..03281c5
--- /dev/null
+++ b/fixtures/Symbols.php
@@ -0,0 +1,23 @@
+<?php
+
+namespace TestNamespace;
+
+class TestClass
+{
+    public $testProperty;
+
+    public function testMethod($testParameter)
+    {
+        $testVariable = 123;
+    }
+}
+
+trait TestTrait
+{
+
+}
+
+interface TestInterface
+{
+
+}
diff --git a/src/Client/TextDocument.php b/src/Client/TextDocument.php
new file mode 100644
index 0000000..20a94d5
--- /dev/null
+++ b/src/Client/TextDocument.php
@@ -0,0 +1,43 @@
+<?php
+declare(strict_types = 1);
+
+namespace LanguageServer\Client;
+
+use AdvancedJsonRpc\Notification as NotificationBody;
+use PhpParser\{Error, Comment, Node, ParserFactory, NodeTraverser, Lexer};
+use PhpParser\NodeVisitor\NameResolver;
+use LanguageServer\ProtocolWriter;
+use LanguageServer\Protocol\{TextDocumentItem, TextDocumentIdentifier, VersionedTextDocumentIdentifier, Message};
+
+/**
+ * Provides method handlers for all textDocument/* methods
+ */
+class TextDocument
+{
+    /**
+     * @var ProtocolWriter
+     */
+    private $protocolWriter;
+
+    public function __construct(ProtocolWriter $protocolWriter)
+    {
+        $this->protocolWriter = $protocolWriter;
+    }
+
+    /**
+     * Diagnostics notification are sent from the server to the client to signal results of validation runs.
+     *
+     * @param string $uri
+     * @param Diagnostic[] $diagnostics
+     */
+    public function publishDiagnostics(string $uri, array $diagnostics)
+    {
+        $this->protocolWriter->write(new Message(new NotificationBody(
+            'textDocument/publishDiagnostics',
+            (object)[
+                'uri' => $uri,
+                'diagnostics' => $diagnostics
+            ]
+        )));
+    }
+}
diff --git a/src/LanguageClient.php b/src/LanguageClient.php
new file mode 100644
index 0000000..4ee5073
--- /dev/null
+++ b/src/LanguageClient.php
@@ -0,0 +1,24 @@
+<?php
+declare(strict_types = 1);
+
+namespace LanguageServer;
+
+use LanguageServer\Client\TextDocument;
+
+class LanguageClient
+{
+    /**
+     * Handles textDocument/* methods
+     *
+     * @var Client\TextDocument
+     */
+    public $textDocument;
+
+    private $protocolWriter;
+
+    public function __construct(ProtocolWriter $writer)
+    {
+        $this->protocolWriter = $writer;
+        $this->textDocument = new TextDocument($writer);
+    }
+}
diff --git a/src/LanguageServer.php b/src/LanguageServer.php
index 39eaeed..8766353 100644
--- a/src/LanguageServer.php
+++ b/src/LanguageServer.php
@@ -2,13 +2,20 @@
 
 namespace LanguageServer;
 
+use LanguageServer\Server\TextDocument;
 use LanguageServer\Protocol\{ServerCapabilities, ClientCapabilities, TextDocumentSyncKind, Message};
 use LanguageServer\Protocol\InitializeResult;
 use AdvancedJsonRpc\{Dispatcher, ResponseError, Response as ResponseBody, Request as RequestBody};
 
 class LanguageServer extends \AdvancedJsonRpc\Dispatcher
 {
+    /**
+     * Handles textDocument/* method calls
+     *
+     * @var Server\TextDocument
+     */
     public $textDocument;
+
     public $telemetry;
     public $window;
     public $workspace;
@@ -17,6 +24,7 @@ class LanguageServer extends \AdvancedJsonRpc\Dispatcher
 
     private $protocolReader;
     private $protocolWriter;
+    private $client;
 
     public function __construct(ProtocolReader $reader, ProtocolWriter $writer)
     {
@@ -47,7 +55,8 @@ class LanguageServer extends \AdvancedJsonRpc\Dispatcher
             }
         });
         $this->protocolWriter = $writer;
-        $this->textDocument = new TextDocumentManager();
+        $this->client = new LanguageClient($writer);
+        $this->textDocument = new Server\TextDocument($this->client);
     }
 
     /**
diff --git a/src/Protocol/PublishDiagnosticsNotification.php b/src/Protocol/PublishDiagnosticsNotification.php
new file mode 100644
index 0000000..b84fd33
--- /dev/null
+++ b/src/Protocol/PublishDiagnosticsNotification.php
@@ -0,0 +1,26 @@
+<?php
+
+namespace LanguageServer\Protocol;
+
+use AdvancedJsonRpc\Notification;
+
+/**
+ * Diagnostics notification are sent from the server to the client to signal results of validation runs.
+ */
+class PublishDiagnosticsNotification extends Notification
+{
+    /**
+     * @var PublishDiagnosticsParams
+     */
+    public $params;
+
+    /**
+     * @param string $uri
+     * @param Diagnostic[] $diagnostics
+     */
+    public function __construct(string $uri, array $diagnostics)
+    {
+        $this->method = 'textDocument/publishDiagnostics';
+        $this->params = $params;
+    }
+}
diff --git a/src/Protocol/PublishDiagnosticsParams.php b/src/Protocol/PublishDiagnosticsParams.php
new file mode 100644
index 0000000..1081187
--- /dev/null
+++ b/src/Protocol/PublishDiagnosticsParams.php
@@ -0,0 +1,22 @@
+<?php
+
+namespace LanguageServer\Protocol\TextDocument;
+
+use LanguageServer\Protocol\Params;
+
+class PublishDiagnosticsParams extends Params
+{
+    /**
+     * The URI for which diagnostic information is reported.
+     *
+     * @var string
+     */
+    public $uri;
+
+    /**
+     * An array of diagnostic information items.
+     *
+     * @var LanguageServer\Protocol\Diagnostic[]
+     */
+    public $diagnostics;
+}
diff --git a/src/Protocol/TextDocumentIdentifier.php b/src/Protocol/TextDocumentIdentifier.php
index f11af85..d19e3cf 100644
--- a/src/Protocol/TextDocumentIdentifier.php
+++ b/src/Protocol/TextDocumentIdentifier.php
@@ -10,4 +10,12 @@ class TextDocumentIdentifier
      * @var string
      */
     public $uri;
+
+    /**
+     * @param string $uri The text document's URI.
+     */
+    public function __construct(string $uri = null)
+    {
+        $this->uri = $uri;
+    }
 }
diff --git a/src/TextDocumentManager.php b/src/Server/TextDocument.php
similarity index 61%
rename from src/TextDocumentManager.php
rename to src/Server/TextDocument.php
index f0825ff..54be2a1 100644
--- a/src/TextDocumentManager.php
+++ b/src/Server/TextDocument.php
@@ -1,15 +1,24 @@
 <?php
 
-namespace LanguageServer;
+namespace LanguageServer\Server;
 
 use PhpParser\{Error, Comment, Node, ParserFactory, NodeTraverser, Lexer};
 use PhpParser\NodeVisitor\NameResolver;
-use LanguageServer\Protocol\{TextDocumentItem, TextDocumentIdentifier, VersionedTextDocumentIdentifier};
+use LanguageServer\{LanguageClient, ColumnCalculator, SymbolFinder};
+use LanguageServer\Protocol\{
+    TextDocumentItem,
+    TextDocumentIdentifier,
+    VersionedTextDocumentIdentifier,
+    Diagnostic,
+    DiagnosticSeverity,
+    Range,
+    Position
+};
 
 /**
  * Provides method handlers for all textDocument/* methods
  */
-class TextDocumentManager
+class TextDocument
 {
     /**
      * @var PhpParser\Parser
@@ -23,8 +32,16 @@ class TextDocumentManager
      */
     private $asts;
 
-    public function __construct()
+    /**
+     * The lanugage client object to call methods on the client
+     *
+     * @var LanguageServer\LanguageClient
+     */
+    private $client;
+
+    public function __construct(LanguageClient $client)
     {
+        $this->client = $client;
         $lexer = new Lexer(['usedAttributes' => ['comments', 'startLine', 'endLine', 'startFilePos', 'endFilePos']]);
         $this->parser = (new ParserFactory)->create(ParserFactory::PREFER_PHP7, $lexer, ['throwOnError' => false]);
     }
@@ -74,20 +91,39 @@ class TextDocumentManager
         $this->updateAst($textDocument->uri, $contentChanges[0]->text);
     }
 
+    /**
+     * Re-parses a source file, updates the AST and reports parsing errors that may occured as diagnostics
+     *
+     * @param string $uri     The URI of the source file
+     * @param string $content The new content of the source file
+     * @return void
+     */
     private function updateAst(string $uri, string $content)
     {
         $stmts = $this->parser->parse($content);
-        // TODO report errors as diagnostics
-        // foreach ($parser->getErrors() as $error) {
-        //     error_log($error->getMessage());
-        // }
+        $diagnostics = [];
+        foreach ($this->parser->getErrors() as $error) {
+            $diagnostic = new Diagnostic();
+            $diagnostic->range = new Range(
+                new Position($error->getStartLine() - 1, $error->hasColumnInfo() ? $error->getStartColumn($content) - 1 : 0),
+                new Position($error->getEndLine() - 1, $error->hasColumnInfo() ? $error->getEndColumn($content) - 1 : 0)
+            );
+            $diagnostic->severity = DiagnosticSeverity::ERROR;
+            $diagnostic->source = 'php';
+            // Do not include "on line ..." in the error message
+            $diagnostic->message = $error->getRawMessage();
+            $diagnostics[] = $diagnostic;
+        }
+        if (count($diagnostics) > 0) {
+            $this->client->textDocument->publishDiagnostics($uri, $diagnostics);
+        }
         // $stmts can be null in case of a fatal parsing error
         if ($stmts) {
             $traverser = new NodeTraverser;
             $traverser->addVisitor(new NameResolver);
             $traverser->addVisitor(new ColumnCalculator($content));
             $traverser->traverse($stmts);
+            $this->asts[$uri] = $stmts;
         }
-        $this->asts[$uri] = $stmts;
     }
 }
diff --git a/src/SymbolFinder.php b/src/SymbolFinder.php
index 0d0b90e..3a48948 100644
--- a/src/SymbolFinder.php
+++ b/src/SymbolFinder.php
@@ -10,6 +10,7 @@ class SymbolFinder extends NodeVisitorAbstract
 {
     const NODE_SYMBOL_KIND_MAP = [
         Node\Stmt\Class_::class           => SymbolKind::CLASS_,
+        Node\Stmt\Trait_::class           => SymbolKind::CLASS_,
         Node\Stmt\Interface_::class       => SymbolKind::INTERFACE,
         Node\Stmt\Namespace_::class       => SymbolKind::NAMESPACE,
         Node\Stmt\Function_::class        => SymbolKind::FUNCTION,
diff --git a/tests/Server/TextDocumentTest.php b/tests/Server/TextDocumentTest.php
new file mode 100644
index 0000000..d80f45e
--- /dev/null
+++ b/tests/Server/TextDocumentTest.php
@@ -0,0 +1,200 @@
+<?php
+declare(strict_types = 1);
+
+namespace LanguageServer\Tests\Server;
+
+use PHPUnit\Framework\TestCase;
+use LanguageServer\Tests\MockProtocolStream;
+use LanguageServer\{Server, Client, LanguageClient};
+use LanguageServer\Protocol\{TextDocumentItem, TextDocumentIdentifier, SymbolKind, DiagnosticSeverity};
+use AdvancedJsonRpc\{Request as RequestBody, Response as ResponseBody};
+
+class TextDocumentTest extends TestCase
+{
+    public function testDocumentSymbol()
+    {
+        $textDocument = new Server\TextDocument(new LanguageClient(new MockProtocolStream()));
+        // Trigger parsing of source
+        $textDocumentItem = new TextDocumentItem();
+        $textDocumentItem->uri = 'whatever';
+        $textDocumentItem->languageId = 'php';
+        $textDocumentItem->version = 1;
+        $textDocumentItem->text = file_get_contents(__DIR__ . '/../../fixtures/Symbols.php');
+        $textDocument->didOpen($textDocumentItem);
+        // Request symbols
+        $result = $textDocument->documentSymbol(new TextDocumentIdentifier('whatever'));
+        $this->assertEquals([
+           [
+                'name' => 'TestNamespace',
+                'kind' => SymbolKind::NAMESPACE,
+                'location' => [
+                    'uri' => 'whatever',
+                    'range' => [
+                        'start' => [
+                            'line' => 2,
+                            'character' => 0
+                        ],
+                        'end' => [
+                            'line' => 2,
+                            'character' => 23
+                        ]
+                    ]
+                ],
+                'containerName' => null
+            ],
+            [
+                'name' => 'TestClass',
+                'kind' => SymbolKind::CLASS_,
+                'location' => [
+                    'uri' => 'whatever',
+                    'range' => [
+                        'start' => [
+                            'line' => 4,
+                            'character' => 0
+                        ],
+                        'end' => [
+                            'line' => 12,
+                            'character' => 0
+                        ]
+                    ]
+                ],
+                'containerName' => null
+            ],
+            [
+                'name' => 'testProperty',
+                'kind' => SymbolKind::PROPERTY,
+                'location' => [
+                    'uri' => 'whatever',
+                    'range' => [
+                        'start' => [
+                            'line' => 6,
+                            'character' => 11
+                        ],
+                        'end' => [
+                            'line' => 6,
+                            'character' => 23
+                        ]
+                    ]
+                ],
+                'containerName' => 'TestClass'
+            ],
+            [
+                'name' => 'testMethod',
+                'kind' => SymbolKind::METHOD,
+                'location' => [
+                    'uri' => 'whatever',
+                    'range' => [
+                        'start' => [
+                            'line' => 8,
+                            'character' => 4
+                        ],
+                        'end' => [
+                            'line' => 11,
+                            'character' => 4
+                        ]
+                    ]
+                ],
+                'containerName' => null
+            ],
+            [
+                'name' => 'testVariable',
+                'kind' => SymbolKind::VARIABLE,
+                'location' => [
+                    'uri' => 'whatever',
+                    'range' => [
+                        'start' => [
+                            'line' => 10,
+                            'character' => 8
+                        ],
+                        'end' => [
+                            'line' => 10,
+                            'character' => 20
+                        ]
+                    ]
+                ],
+                'containerName' => null
+            ],
+            [
+                'name' => 'TestTrait',
+                'kind' => SymbolKind::CLASS_,
+                'location' => [
+                    'uri' => 'whatever',
+                    'range' => [
+                        'start' => [
+                            'line' => 14,
+                            'character' => 0
+                        ],
+                        'end' => [
+                            'line' => 17,
+                            'character' => 0
+                        ]
+                    ]
+                ],
+                'containerName' => null
+            ],
+            [
+                'name' => 'TestInterface',
+                'kind' => SymbolKind::INTERFACE,
+                'location' => [
+                    'uri' => 'whatever',
+                    'range' => [
+                        'start' => [
+                            'line' => 19,
+                            'character' => 0
+                        ],
+                        'end' => [
+                            'line' => 22,
+                            'character' => 0
+                        ]
+                    ]
+                ],
+                'containerName' => null
+            ]
+        ], json_decode(json_encode($result), true));
+    }
+
+    public function testParseErrorsArePublishedAsDiagnostics()
+    {
+        $args = null;
+        $client = new LanguageClient(new MockProtocolStream());
+        $client->textDocument = new class($args) extends Client\TextDocument {
+            private $args;
+            public function __construct(&$args)
+            {
+                parent::__construct(new MockProtocolStream());
+                $this->args = &$args;
+            }
+            public function publishDiagnostics(string $uri, array $diagnostics)
+            {
+                $this->args = func_get_args();
+            }
+        };
+        $textDocument = new Server\TextDocument($client);
+        // Trigger parsing of source
+        $textDocumentItem = new TextDocumentItem();
+        $textDocumentItem->uri = 'whatever';
+        $textDocumentItem->languageId = 'php';
+        $textDocumentItem->version = 1;
+        $textDocumentItem->text = file_get_contents(__DIR__ . '/../../fixtures/InvalidFile.php');
+        $textDocument->didOpen($textDocumentItem);
+        $this->assertEquals([
+            'whatever',
+            [[
+                'range' => [
+                    'start' => [
+                        'line' => 2,
+                        'character' => 10
+                    ],
+                    'end' => [
+                        'line' => 2,
+                        'character' => 14
+                    ]
+                ],
+                'severity' => DiagnosticSeverity::ERROR,
+                'code' => null,
+                'source' => 'php',
+                'message' => "Syntax error, unexpected T_CLASS, expecting T_STRING"
+            ]]
+        ], json_decode(json_encode($args), true));
+    }
+}