diff --git a/gtkblueprinttool/ast.py b/gtkblueprinttool/ast.py
index f7d6c44..831bbdb 100644
--- a/gtkblueprinttool/ast.py
+++ b/gtkblueprinttool/ast.py
@@ -88,6 +88,8 @@ class AstNode:
                 if docs is not None:
                     return docs
 
+        return None
+
 
 class UI(AstNode):
     """ The AST node for the entire file """
diff --git a/gtkblueprinttool/errors.py b/gtkblueprinttool/errors.py
index 14142dc..16d01a6 100644
--- a/gtkblueprinttool/errors.py
+++ b/gtkblueprinttool/errors.py
@@ -18,6 +18,7 @@
 # SPDX-License-Identifier: LGPL-3.0-or-later
 
 
+import typing as T
 import sys, traceback
 from . import utils
 
@@ -60,7 +61,7 @@ class CompileError(PrintableError):
         return self
 
 
-    def _did_you_mean(self, word: str, options: [str]):
+    def _did_you_mean(self, word: str, options: T.List[str]):
         if word.replace("_", "-") in options:
             self.hint(f"use '-', not '_': `{word.replace('_', '-')}`")
             return
@@ -98,11 +99,11 @@ class MultipleErrors(PrintableError):
     a list and re-thrown using the MultipleErrors exception. It will
     pretty-print all of the errors and a count of how many errors there are. """
 
-    def __init__(self, errors: [CompileError]):
+    def __init__(self, errors: T.List[CompileError]):
         super().__init__()
         self.errors = errors
 
-    def pretty_print(self, filename, code) -> str:
+    def pretty_print(self, filename, code) -> None:
         for error in self.errors:
             error.pretty_print(filename, code)
         if len(self.errors) != 1:
diff --git a/gtkblueprinttool/gir.py b/gtkblueprinttool/gir.py
index 3441494..4ab7868 100644
--- a/gtkblueprinttool/gir.py
+++ b/gtkblueprinttool/gir.py
@@ -17,6 +17,7 @@
 #
 # SPDX-License-Identifier: LGPL-3.0-or-later
 
+import typing as T
 import os, sys
 
 from .errors import CompileError, CompilerBugError
@@ -24,7 +25,7 @@ from .utils import lazy_prop
 from . import xml_reader
 
 
-extra_search_paths = []
+extra_search_paths: T.List[str] = []
 _namespace_cache = {}
 
 _search_paths = []
@@ -71,7 +72,7 @@ class GirNode:
         return self.xml.get("version")
 
     @lazy_prop
-    def doc(self) -> str:
+    def doc(self) -> T.Optional[str]:
         el = self.xml.get_elements("doc")
         if len(el) != 1:
             return None
@@ -175,7 +176,7 @@ class Repository(GirNode):
         try:
             self.includes = { include["name"]: get_namespace(include["name"], include["version"]) for include in xml.get_elements("include") }
         except:
-            raise CompilerBugError(f"Failed to load dependencies of {namespace}-{version}")
+            raise CompilerBugError(f"Failed to load dependencies.")
 
     def lookup_namespace(self, name: str):
         ns = self.namespaces.get(name)
@@ -195,7 +196,7 @@ class GirContext:
     def add_namespace(self, namespace: Namespace):
         other = self.namespaces.get(namespace.name)
         if other is not None and other.version != namespace.version:
-            raise CompileError(f"Namespace {namespace}-{version} can't be imported because version {other.version} was imported earlier")
+            raise CompileError(f"Namespace {namespace.name}-{namespace.version} can't be imported because version {other.version} was imported earlier")
 
         self.namespaces[namespace.name] = namespace
 
diff --git a/gtkblueprinttool/lsp.py b/gtkblueprinttool/lsp.py
index 1ac2756..e326315 100644
--- a/gtkblueprinttool/lsp.py
+++ b/gtkblueprinttool/lsp.py
@@ -18,6 +18,7 @@
 # SPDX-License-Identifier: LGPL-3.0-or-later
 
 
+import typing as T
 import json, sys, traceback
 
 from .errors import PrintableError, CompileError, MultipleErrors
@@ -33,7 +34,7 @@ def command(json_method):
 
 
 class LanguageServer:
-    commands = {}
+    commands: T.Dict[str, T.Callable[[LanguageServer, T.Union[str, int], T.Any], None]] = {}
 
     def __init__(self):
         self.client_capabilities = {}
diff --git a/gtkblueprinttool/parse_tree.py b/gtkblueprinttool/parse_tree.py
index f799925..72b8301 100644
--- a/gtkblueprinttool/parse_tree.py
+++ b/gtkblueprinttool/parse_tree.py
@@ -19,6 +19,9 @@
 
 """ Utilities for parsing an AST from a token stream. """
 
+import typing as T
+
+from collections import defaultdict
 from enum import Enum
 
 from .ast import AstNode
@@ -27,7 +30,12 @@ from .tokenizer import Token, TokenType
 
 
 _SKIP_TOKENS = [TokenType.COMMENT, TokenType.WHITESPACE]
-_RECOVER_TOKENS = [TokenType.COMMENT, TokenType.STMT_END, TokenType.CLOSE_BLOCK, TokenType.EOF]
+_RECOVER_TOKENS = [
+    TokenType.COMMENT,
+    TokenType.STMT_END,
+    TokenType.CLOSE_BLOCK,
+    TokenType.EOF,
+]
 
 
 class ParseResult(Enum):
@@ -59,9 +67,9 @@ class ParseGroup:
 
     def __init__(self, ast_type, start: int):
         self.ast_type = ast_type
-        self.children = {}
-        self.keys = {}
-        self.tokens = {}
+        self.children: T.Dict[str, T.List[ParseGroup]] = defaultdict()
+        self.keys: T.Dict[str, T.Any] = {}
+        self.tokens: T.Dict[str, Token] = {}
         self.start = start
         self.end = None
 
@@ -195,6 +203,9 @@ class ParseNode:
         else:
             return ParseResult.FAILURE
 
+    def _parse(self, ctx: ParseContext) -> bool:
+        raise NotImplementedError()
+
     def err(self, message):
         """ Causes this ParseNode to raise an exception if it fails to parse.
         This prevents the parser from backtracking, so you should understand
@@ -346,7 +357,7 @@ class Optional(ParseNode):
 class StaticToken(ParseNode):
     """ Base class for ParseNodes that match a token type without inspecting
     the token's contents. """
-    token_type = None
+    token_type: T.Optional[TokenType] = None
 
     def _parse(self, ctx: ParseContext) -> bool:
         return ctx.next_token().type == self.token_type
diff --git a/gtkblueprinttool/tokenizer.py b/gtkblueprinttool/tokenizer.py
index 2f06381..80d6fe8 100644
--- a/gtkblueprinttool/tokenizer.py
+++ b/gtkblueprinttool/tokenizer.py
@@ -18,6 +18,7 @@
 # SPDX-License-Identifier: LGPL-3.0-or-later
 
 
+import typing as T
 import re
 from enum import Enum
 
@@ -43,7 +44,7 @@ class TokenType(Enum):
     COMMA           = 15
 
 
-_TOKENS = [
+_tokens = [
     (TokenType.DIRECTIVE,       r"@[\d\w\-_]+"),
     (TokenType.IDENT,           r"[A-Za-z_][\d\w\-_]*"),
     (TokenType.QUOTED,          r'"(\\"|[^"\n])+"'),
@@ -63,7 +64,7 @@ _TOKENS = [
     (TokenType.OP,              r"[:=\.=\|<>\+\-/\*]+"),
     (TokenType.COMMA,           r"\,"),
 ]
-_TOKENS = [(type, re.compile(regex)) for (type, regex) in _TOKENS]
+_TOKENS = [(type, re.compile(regex)) for (type, regex) in _tokens]
 
 
 class Token:
@@ -111,5 +112,5 @@ def _tokenize(ui_ml: str):
     yield Token(TokenType.EOF, i, i, ui_ml)
 
 
-def tokenize(data: str) -> [Token]:
+def tokenize(data: str) -> T.List[Token]:
     return list(_tokenize(data))
diff --git a/gtkblueprinttool/utils.py b/gtkblueprinttool/utils.py
index eb632cc..a4a9bbd 100644
--- a/gtkblueprinttool/utils.py
+++ b/gtkblueprinttool/utils.py
@@ -32,7 +32,7 @@ def lazy_prop(func):
     return real_func
 
 
-def did_you_mean(word: str, options: [str]) -> T.Optional[str]:
+def did_you_mean(word: str, options: T.List[str]) -> T.Optional[str]:
     if len(options) == 0:
         return None
 
@@ -67,7 +67,7 @@ def did_you_mean(word: str, options: [str]) -> T.Optional[str]:
     return None
 
 
-def idx_to_pos(idx: int, text: str) -> (int, int):
+def idx_to_pos(idx: int, text: str) -> T.Tuple[int, int]:
     if idx == 0:
         return (0, 0)
     sp = text[:idx].splitlines(keepends=True)