diff --git a/gtkblueprinttool/ast.py b/gtkblueprinttool/ast.py
index 2ef4960..4457045 100644
--- a/gtkblueprinttool/ast.py
+++ b/gtkblueprinttool/ast.py
@@ -167,11 +167,21 @@ class Template(AstNode):
 
 
 class Object(AstNode):
-    @validate("namespace", "class_name")
-    def gir_class_exists(self):
+    @validate("namespace")
+    def gir_ns_exists(self):
         if not self.tokens["ignore_gir"]:
+            self.root.gir.validate_ns(self.tokens["namespace"])
+
+    @validate("class_name")
+    def gir_class_exists(self):
+        if not self.tokens["ignore_gir"] and self.gir_ns is not None:
             self.root.gir.validate_class(self.tokens["class_name"], self.tokens["namespace"])
 
+    @property
+    def gir_ns(self):
+        if not self.tokens["ignore_gir"]:
+            return self.root.gir.namespaces.get(self.tokens["namespace"])
+
     @property
     def gir_class(self):
         if not self.tokens["ignore_gir"]:
@@ -180,7 +190,8 @@ class Object(AstNode):
 
     @docs("namespace")
     def namespace_docs(self):
-        return self.root.gir.namespaces[self.tokens["namespace"]].doc
+        if ns := self.root.gir.namespaces.get(self.tokens["namespace"]):
+            return ns.doc
 
 
     @docs("class_name")
@@ -398,17 +409,17 @@ class IdentValue(Value):
             if self.tokens["value"] not in type.members:
                 raise CompileError(
                     f"{self.tokens['value']} is not a member of {type.full_name}",
-                    did_you_mean=type.members.keys(),
+                    did_you_mean=(self.tokens['value'], type.members.keys()),
                 )
 
         elif isinstance(type, gir.BoolType):
             # would have been parsed as a LiteralValue if it was correct
             raise CompileError(
                 f"Expected 'true' or 'false' for boolean value",
-                did_you_mean=["true", "false"],
+                did_you_mean=(self.tokens['value'], ["true", "false"]),
             )
 
-        else:
+        elif type is not None:
             object = self.root.objects_by_id.get(self.tokens["value"])
             if object is None:
                 raise CompileError(
diff --git a/gtkblueprinttool/errors.py b/gtkblueprinttool/errors.py
index 599138e..41d4ce9 100644
--- a/gtkblueprinttool/errors.py
+++ b/gtkblueprinttool/errors.py
@@ -17,7 +17,7 @@
 #
 # SPDX-License-Identifier: LGPL-3.0-or-later
 
-
+from dataclasses import dataclass
 import typing as T
 import sys, traceback
 from . import utils
@@ -45,13 +45,14 @@ class CompileError(PrintableError):
 
     category = "error"
 
-    def __init__(self, message, start=None, end=None, did_you_mean=None, hints=None):
+    def __init__(self, message, start=None, end=None, did_you_mean=None, hints=None, actions=None):
         super().__init__(message)
 
         self.message = message
         self.start = start
         self.end = end
         self.hints = hints or []
+        self.actions = actions or []
 
         if did_you_mean is not None:
             self._did_you_mean(*did_you_mean)
@@ -72,6 +73,7 @@ class CompileError(PrintableError):
                 self.hint(f"Did you mean `{recommend}` (note the capitalization)?")
             else:
                 self.hint(f"Did you mean `{recommend}`?")
+            self.actions.append(CodeAction(f"Change to `{recommend}`", recommend))
         else:
             self.hint("Did you check your spelling?")
             self.hint("Are your dependencies up to date?")
@@ -92,6 +94,12 @@ at {filename} line {line_num} column {col_num}:
         print()
 
 
+@dataclass
+class CodeAction:
+    title: str
+    replace_with: str
+
+
 class AlreadyCaughtError(Exception):
     """ Emitted when a validation has already failed and its error message
     should not be repeated. """
diff --git a/gtkblueprinttool/gir.py b/gtkblueprinttool/gir.py
index dfde6ab..c59bba7 100644
--- a/gtkblueprinttool/gir.py
+++ b/gtkblueprinttool/gir.py
@@ -388,9 +388,9 @@ class GirContext:
             return None
 
 
-    def validate_class(self, name: str, ns: str):
+    def validate_ns(self, ns: str):
         """ Raises an exception if there is a problem looking up the given
-        class (it doesn't exist, it isn't a class, etc.) """
+        namespace. """
 
         ns = ns or "Gtk"
 
@@ -400,6 +400,14 @@ class GirContext:
                 did_you_mean=(ns, self.namespaces.keys()),
             )
 
+
+    def validate_class(self, name: str, ns: str):
+        """ Raises an exception if there is a problem looking up the given
+        class (it doesn't exist, it isn't a class, etc.) """
+
+        ns = ns or "Gtk"
+        self.validate_ns(ns)
+
         type = self.get_type(name, ns)
 
         if type is None:
diff --git a/gtkblueprinttool/lsp.py b/gtkblueprinttool/lsp.py
index 0c58f45..23fe63f 100644
--- a/gtkblueprinttool/lsp.py
+++ b/gtkblueprinttool/lsp.py
@@ -164,6 +164,7 @@ class LanguageServer:
                     "full": True,
                 },
                 "completionProvider": {},
+                "codeActionProvider": {},
                 "hoverProvider": True,
             }
         })
@@ -226,6 +227,35 @@ class LanguageServer:
         })
 
 
+    @command("textDocument/codeAction")
+    def code_actions(self, id, params):
+        open_file = self._open_files[params["textDocument"]["uri"]]
+
+        range_start = utils.pos_to_idx(params["range"]["start"]["line"], params["range"]["start"]["character"], open_file.text)
+        range_end = utils.pos_to_idx(params["range"]["end"]["line"], params["range"]["end"]["character"], open_file.text)
+
+        actions = [
+            {
+                "title": action.title,
+                "kind": "quickfix",
+                "diagnostics": [self._create_diagnostic(open_file.text, diagnostic)],
+                "edit": {
+                    "changes": {
+                        open_file.uri: [{
+                            "range": utils.idxs_to_range(diagnostic.start, diagnostic.end, open_file.text),
+                            "newText": action.replace_with
+                        }]
+                    }
+                }
+            }
+            for diagnostic in open_file.diagnostics
+            if not (diagnostic.end < range_start or diagnostic.start > range_end)
+            for action in diagnostic.actions
+        ]
+
+        self._send_response(id, actions)
+
+
     def _send_file_updates(self, open_file: OpenFile):
         self._send_notification("textDocument/publishDiagnostics", {
             "uri": open_file.uri,
@@ -233,13 +263,8 @@ class LanguageServer:
         })
 
     def _create_diagnostic(self, text, err):
-        start_l, start_c = utils.idx_to_pos(err.start, text)
-        end_l, end_c = utils.idx_to_pos(err.end or err.start, text)
         return {
-            "range": {
-                "start": { "line": start_l, "character": start_c },
-                "end": { "line": end_l, "character": end_c },
-            },
+            "range": utils.idxs_to_range(err.start, err.end, text),
             "message": err.message,
             "severity": 1,
         }
diff --git a/gtkblueprinttool/utils.py b/gtkblueprinttool/utils.py
index cf733c7..0954bc4 100644
--- a/gtkblueprinttool/utils.py
+++ b/gtkblueprinttool/utils.py
@@ -78,3 +78,17 @@ def idx_to_pos(idx: int, text: str) -> T.Tuple[int, int]:
 def pos_to_idx(line: int, col: int, text: str) -> int:
     lines = text.splitlines(keepends=True)
     return sum([len(line) for line in lines[:line]]) + col
+
+def idxs_to_range(start: int, end: int, text: str):
+    start_l, start_c = idx_to_pos(start, text)
+    end_l, end_c = idx_to_pos(end, text)
+    return {
+        "start": {
+            "line": start_l,
+            "character": start_c,
+        },
+        "end": {
+            "line": end_l,
+            "character": end_c,
+        },
+    }