diff --git a/toolchain/driver/driver.cpp b/toolchain/driver/driver.cpp
index d62d6ba72f35..f0663a91fcc4 100644
--- a/toolchain/driver/driver.cpp
+++ b/toolchain/driver/driver.cpp
@@ -152,7 +152,7 @@ auto Driver::RunDumpParseTreeSubcommand(llvm::ArrayRef<llvm::StringRef> args)
   auto parse_tree =
       ParseTree::Parse(tokenized_source, ConsoleDiagnosticConsumer());
   parse_tree.Print(output_stream_);
-  return !tokenized_source.has_errors() && !parse_tree.HasErrors();
+  return !tokenized_source.has_errors() && !parse_tree.has_errors();
 }
 
 auto Driver::ReportExtraArgs(llvm::StringRef subcommand_text,
diff --git a/toolchain/parser/parse_node_kind.cpp b/toolchain/parser/parse_node_kind.cpp
index b8c2701e6301..d26eb33acf36 100644
--- a/toolchain/parser/parse_node_kind.cpp
+++ b/toolchain/parser/parse_node_kind.cpp
@@ -8,7 +8,7 @@
 
 namespace Carbon {
 
-auto ParseNodeKind::GetName() const -> llvm::StringRef {
+auto ParseNodeKind::name() const -> llvm::StringRef {
   static constexpr llvm::StringLiteral Names[] = {
 #define CARBON_PARSE_NODE_KIND(Name) #Name,
 #include "toolchain/parser/parse_node_kind.def"
diff --git a/toolchain/parser/parse_node_kind.h b/toolchain/parser/parse_node_kind.h
index 05729b9a3dbc..bbd343734d0c 100644
--- a/toolchain/parser/parse_node_kind.h
+++ b/toolchain/parser/parse_node_kind.h
@@ -52,7 +52,7 @@ class ParseNodeKind {
   }
 
   // Gets a friendly name for the token for logging or debugging.
-  [[nodiscard]] auto GetName() const -> llvm::StringRef;
+  [[nodiscard]] auto name() const -> llvm::StringRef;
 
   // Enable conversion to our private enum, including in a `constexpr` context,
   // to enable usage in `switch` and `case`. The enum remains private and
diff --git a/toolchain/parser/parse_node_kind_test.cpp b/toolchain/parser/parse_node_kind_test.cpp
index 50a7c0eaf141..3bd9aec56d7b 100644
--- a/toolchain/parser/parse_node_kind_test.cpp
+++ b/toolchain/parser/parse_node_kind_test.cpp
@@ -15,9 +15,9 @@ namespace {
 
 // Not much to test here, so just verify that the API compiles and returns the
 // data in the `.def` file.
-#define CARBON_PARSE_NODE_KIND(Name)                   \
-  TEST(ParseNodeKindTest, Name) {                      \
-    EXPECT_EQ(#Name, ParseNodeKind::Name().GetName()); \
+#define CARBON_PARSE_NODE_KIND(Name)                \
+  TEST(ParseNodeKindTest, Name) {                   \
+    EXPECT_EQ(#Name, ParseNodeKind::Name().name()); \
   }
 #include "toolchain/parser/parse_node_kind.def"
 
diff --git a/toolchain/parser/parse_test_helpers.h b/toolchain/parser/parse_test_helpers.h
index 1141c42df5be..70af7bd291c4 100644
--- a/toolchain/parser/parse_test_helpers.h
+++ b/toolchain/parser/parse_test_helpers.h
@@ -77,7 +77,7 @@ inline auto ExpectedNodesMatcher::MatchAndExplain(
     -> bool {
   auto& output = *output_ptr;
   bool matches = true;
-  const auto rpo = llvm::reverse(tree.Postorder());
+  const auto rpo = llvm::reverse(tree.postorder());
   const auto nodes_begin = rpo.begin();
   const auto nodes_end = rpo.end();
   auto nodes_it = nodes_begin;
@@ -92,7 +92,7 @@ inline auto ExpectedNodesMatcher::MatchAndExplain(
     }
 
     ParseTree::Node n = *nodes_it++;
-    int postorder_index = n.GetIndex();
+    int postorder_index = n.index();
 
     const ExpectedNode& expected_node = *expected_node_stack.pop_back_val();
 
@@ -104,7 +104,7 @@ inline auto ExpectedNodesMatcher::MatchAndExplain(
       CHECK(expected_node.children.empty())
           << "Must not skip an expected subtree while specifying expected "
              "children!";
-      nodes_it = llvm::reverse(tree.Postorder(n)).end();
+      nodes_it = llvm::reverse(tree.postorder(n)).end();
       continue;
     }
 
@@ -112,7 +112,7 @@ inline auto ExpectedNodesMatcher::MatchAndExplain(
     // ahead in the tree to ensure that the number of children of this node and
     // the expected number of children match.
     int num_children =
-        std::distance(tree.Children(n).begin(), tree.Children(n).end());
+        std::distance(tree.children(n).begin(), tree.children(n).end());
     if (num_children != static_cast<int>(expected_node.children.size())) {
       output
           << "\nParse node (postorder index #" << postorder_index << ") has "
@@ -120,7 +120,7 @@ inline auto ExpectedNodesMatcher::MatchAndExplain(
           << expected_node.children.size()
           << ". Skipping this subtree to avoid any unsynchronized tree walk.";
       matches = false;
-      nodes_it = llvm::reverse(tree.Postorder(n)).end();
+      nodes_it = llvm::reverse(tree.postorder(n)).end();
       continue;
     }
 
@@ -181,7 +181,7 @@ inline auto ExpectedNodesMatcher::DescribeTo(std::ostream* output_ptr) const
     for (int indent_count = 0; indent_count < depth; ++indent_count) {
       output << "  ";
     }
-    output << "{kind: '" << expected_node.kind.GetName().str() << "'";
+    output << "{kind: '" << expected_node.kind.name().str() << "'";
     if (!expected_node.text.empty()) {
       output << ", text: '" << expected_node.text << "'";
     }
@@ -229,17 +229,17 @@ inline auto ExpectedNodesMatcher::MatchExpectedNode(
     ::testing::MatchResultListener& output) const -> bool {
   bool matches = true;
 
-  ParseNodeKind kind = tree.GetNodeKind(n);
+  ParseNodeKind kind = tree.node_kind(n);
   if (kind != expected_node.kind) {
     output << "\nParse node (postorder index #" << postorder_index << ") is a "
-           << kind.GetName().str() << ", expected a "
-           << expected_node.kind.GetName().str() << ".";
+           << kind.name().str() << ", expected a "
+           << expected_node.kind.name().str() << ".";
     matches = false;
   }
 
-  if (tree.HasErrorInNode(n) != expected_node.has_error) {
+  if (tree.node_has_error(n) != expected_node.has_error) {
     output << "\nParse node (postorder index #" << postorder_index << ") "
-           << (tree.HasErrorInNode(n) ? "has an error"
+           << (tree.node_has_error(n) ? "has an error"
                                       : "does not have an error")
            << ", expected that it "
            << (expected_node.has_error ? "has an error"
diff --git a/toolchain/parser/parse_tree.cpp b/toolchain/parser/parse_tree.cpp
index da1f8cffde5e..5df5d96b4911 100644
--- a/toolchain/parser/parse_tree.cpp
+++ b/toolchain/parser/parse_tree.cpp
@@ -30,12 +30,12 @@ auto ParseTree::Parse(TokenizedBuffer& tokens, DiagnosticConsumer& consumer)
   return Parser::Parse(tokens, emitter);
 }
 
-auto ParseTree::Postorder() const -> llvm::iterator_range<PostorderIterator> {
+auto ParseTree::postorder() const -> llvm::iterator_range<PostorderIterator> {
   return {PostorderIterator(Node(0)),
           PostorderIterator(Node(node_impls_.size()))};
 }
 
-auto ParseTree::Postorder(Node n) const
+auto ParseTree::postorder(Node n) const
     -> llvm::iterator_range<PostorderIterator> {
   // The postorder ends after this node, the root, and begins at the start of
   // its subtree.
@@ -45,28 +45,28 @@ auto ParseTree::Postorder(Node n) const
           PostorderIterator(Node(end_index))};
 }
 
-auto ParseTree::Children(Node n) const
+auto ParseTree::children(Node n) const
     -> llvm::iterator_range<SiblingIterator> {
   int end_index = n.index_ - node_impls_[n.index_].subtree_size;
   return {SiblingIterator(*this, Node(n.index_ - 1)),
           SiblingIterator(*this, Node(end_index))};
 }
 
-auto ParseTree::Roots() const -> llvm::iterator_range<SiblingIterator> {
+auto ParseTree::roots() const -> llvm::iterator_range<SiblingIterator> {
   return {
       SiblingIterator(*this, Node(static_cast<int>(node_impls_.size()) - 1)),
       SiblingIterator(*this, Node(-1))};
 }
 
-auto ParseTree::HasErrorInNode(Node n) const -> bool {
+auto ParseTree::node_has_error(Node n) const -> bool {
   return node_impls_[n.index_].has_error;
 }
 
-auto ParseTree::GetNodeKind(Node n) const -> ParseNodeKind {
+auto ParseTree::node_kind(Node n) const -> ParseNodeKind {
   return node_impls_[n.index_].kind;
 }
 
-auto ParseTree::GetNodeToken(Node n) const -> TokenizedBuffer::Token {
+auto ParseTree::node_token(Node n) const -> TokenizedBuffer::Token {
   return node_impls_[n.index_].token;
 }
 
@@ -85,7 +85,7 @@ auto ParseTree::Print(llvm::raw_ostream& output) const -> void {
   // The roots, like siblings, are in RPO (so reversed), but we add them in
   // order here because we'll pop off the stack effectively reversing then.
   llvm::SmallVector<std::pair<Node, int>, 16> node_stack;
-  for (Node n : Roots()) {
+  for (Node n : roots()) {
     node_stack.push_back({n, 0});
   }
 
@@ -93,16 +93,15 @@ auto ParseTree::Print(llvm::raw_ostream& output) const -> void {
     Node n;
     int depth;
     std::tie(n, depth) = node_stack.pop_back_val();
-    auto& n_impl = node_impls_[n.GetIndex()];
+    auto& n_impl = node_impls_[n.index()];
 
     for (int unused_indent : llvm::seq(0, depth)) {
       (void)unused_indent;
       output << "  ";
     }
 
-    output << "{node_index: " << n.index_ << ", kind: '"
-           << n_impl.kind.GetName() << "', text: '"
-           << tokens_->GetTokenText(n_impl.token) << "'";
+    output << "{node_index: " << n.index_ << ", kind: '" << n_impl.kind.name()
+           << "', text: '" << tokens_->GetTokenText(n_impl.token) << "'";
 
     if (n_impl.has_error) {
       output << ", has_error: yes";
@@ -114,7 +113,7 @@ auto ParseTree::Print(llvm::raw_ostream& output) const -> void {
       output << ", children: [\n";
       // We append the children in order here as well because they will get
       // reversed when popped off the stack.
-      for (Node sibling_n : Children(n)) {
+      for (Node sibling_n : children(n)) {
         node_stack.push_back({sibling_n, depth + 1});
       }
       continue;
@@ -142,12 +141,12 @@ auto ParseTree::Print(llvm::raw_ostream& output) const -> void {
 auto ParseTree::Verify() const -> bool {
   // Verify basic tree structure invariants.
   llvm::SmallVector<ParseTree::Node, 16> ancestors;
-  for (Node n : llvm::reverse(Postorder())) {
-    auto& n_impl = node_impls_[n.GetIndex()];
+  for (Node n : llvm::reverse(postorder())) {
+    auto& n_impl = node_impls_[n.index()];
 
     if (n_impl.has_error && !has_errors_) {
       llvm::errs()
-          << "Node #" << n.GetIndex()
+          << "Node #" << n.index()
           << " has errors, but the tree is not marked as having any.\n";
       return false;
     }
@@ -155,14 +154,14 @@ auto ParseTree::Verify() const -> bool {
     if (n_impl.subtree_size > 1) {
       if (!ancestors.empty()) {
         auto parent_n = ancestors.back();
-        auto& parent_n_impl = node_impls_[parent_n.GetIndex()];
-        int end_index = n.GetIndex() - n_impl.subtree_size;
-        int parent_end_index = parent_n.GetIndex() - parent_n_impl.subtree_size;
+        auto& parent_n_impl = node_impls_[parent_n.index()];
+        int end_index = n.index() - n_impl.subtree_size;
+        int parent_end_index = parent_n.index() - parent_n_impl.subtree_size;
         if (parent_end_index > end_index) {
-          llvm::errs() << "Node #" << n.GetIndex() << " has a subtree size of "
+          llvm::errs() << "Node #" << n.index() << " has a subtree size of "
                        << n_impl.subtree_size
                        << " which extends beyond its parent's (node #"
-                       << parent_n.GetIndex() << ") subtree (size "
+                       << parent_n.index() << ") subtree (size "
                        << parent_n_impl.subtree_size << ")\n";
           return false;
         }
@@ -173,7 +172,7 @@ auto ParseTree::Verify() const -> bool {
     }
 
     if (n_impl.subtree_size < 1) {
-      llvm::errs() << "Node #" << n.GetIndex()
+      llvm::errs() << "Node #" << n.index()
                    << " has an invalid subtree size of " << n_impl.subtree_size
                    << "!\n";
       return false;
@@ -181,11 +180,11 @@ auto ParseTree::Verify() const -> bool {
 
     // We're going to pop off some levels of the tree. Check each ancestor to
     // make sure the offsets are correct.
-    int next_index = n.GetIndex() - 1;
+    int next_index = n.index() - 1;
     while (!ancestors.empty()) {
       ParseTree::Node parent_n = ancestors.back();
-      if ((parent_n.GetIndex() -
-           node_impls_[parent_n.GetIndex()].subtree_size) != next_index) {
+      if ((parent_n.index() - node_impls_[parent_n.index()].subtree_size) !=
+          next_index) {
         break;
       }
       ancestors.pop_back();
@@ -195,7 +194,7 @@ auto ParseTree::Verify() const -> bool {
     llvm::errs()
         << "Finished walking the parse tree and there are still ancestors:\n";
     for (Node ancestor_n : ancestors) {
-      llvm::errs() << "  Node #" << ancestor_n.GetIndex() << "\n";
+      llvm::errs() << "  Node #" << ancestor_n.index() << "\n";
     }
     return false;
   }
@@ -204,17 +203,17 @@ auto ParseTree::Verify() const -> bool {
 }
 
 auto ParseTree::Node::Print(llvm::raw_ostream& output) const -> void {
-  output << GetIndex();
+  output << index();
 }
 
 auto ParseTree::PostorderIterator::Print(llvm::raw_ostream& output) const
     -> void {
-  output << node_.GetIndex();
+  output << node_.index();
 }
 
 auto ParseTree::SiblingIterator::Print(llvm::raw_ostream& output) const
     -> void {
-  output << node_.GetIndex();
+  output << node_.index();
 }
 
 }  // namespace Carbon
diff --git a/toolchain/parser/parse_tree.h b/toolchain/parser/parse_tree.h
index f8378494c603..8ef69958f66b 100644
--- a/toolchain/parser/parse_tree.h
+++ b/toolchain/parser/parse_tree.h
@@ -58,41 +58,41 @@ class ParseTree {
       -> ParseTree;
 
   // Tests whether there are any errors in the parse tree.
-  [[nodiscard]] auto HasErrors() const -> bool { return has_errors_; }
+  [[nodiscard]] auto has_errors() const -> bool { return has_errors_; }
 
   // Returns the number of nodes in this parse tree.
-  [[nodiscard]] auto Size() const -> int { return node_impls_.size(); }
+  [[nodiscard]] auto size() const -> int { return node_impls_.size(); }
 
   // Returns an iterable range over the parse tree nodes in depth-first
   // postorder.
-  [[nodiscard]] auto Postorder() const
+  [[nodiscard]] auto postorder() const
       -> llvm::iterator_range<PostorderIterator>;
 
   // Returns an iterable range over the parse tree node and all of its
   // descendants in depth-first postorder.
-  [[nodiscard]] auto Postorder(Node n) const
+  [[nodiscard]] auto postorder(Node n) const
       -> llvm::iterator_range<PostorderIterator>;
 
   // Returns an iterable range over the direct children of a node in the parse
   // tree. This is a forward range, but is constant time to increment. The order
   // of children is the same as would be found in a reverse postorder traversal.
-  [[nodiscard]] auto Children(Node n) const
+  [[nodiscard]] auto children(Node n) const
       -> llvm::iterator_range<SiblingIterator>;
 
   // Returns an iterable range over the roots of the parse tree. This is a
   // forward range, but is constant time to increment. The order of roots is the
   // same as would be found in a reverse postorder traversal.
-  [[nodiscard]] auto Roots() const -> llvm::iterator_range<SiblingIterator>;
+  [[nodiscard]] auto roots() const -> llvm::iterator_range<SiblingIterator>;
 
   // Tests whether a particular node contains an error and may not match the
   // full expected structure of the grammar.
-  [[nodiscard]] auto HasErrorInNode(Node n) const -> bool;
+  [[nodiscard]] auto node_has_error(Node n) const -> bool;
 
   // Returns the kind of the given parse tree node.
-  [[nodiscard]] auto GetNodeKind(Node n) const -> ParseNodeKind;
+  [[nodiscard]] auto node_kind(Node n) const -> ParseNodeKind;
 
   // Returns the token the given parse tree node models.
-  [[nodiscard]] auto GetNodeToken(Node n) const -> TokenizedBuffer::Token;
+  [[nodiscard]] auto node_token(Node n) const -> TokenizedBuffer::Token;
 
   // Returns the text backing the token for the given node.
   //
@@ -254,7 +254,7 @@ class ParseTree::Node {
   // should not expect any particular semantics from this value.
   //
   // FIXME: Maybe we can switch to stream operator overloads?
-  [[nodiscard]] auto GetIndex() const -> int { return index_; }
+  [[nodiscard]] auto index() const -> int { return index_; }
 
   // Prints the node index.
   auto Print(llvm::raw_ostream& output) const -> void;
diff --git a/toolchain/parser/parse_tree_fuzzer.cpp b/toolchain/parser/parse_tree_fuzzer.cpp
index 59dc9e8a29c2..9b0dabe946c9 100644
--- a/toolchain/parser/parse_tree_fuzzer.cpp
+++ b/toolchain/parser/parse_tree_fuzzer.cpp
@@ -36,13 +36,13 @@ extern "C" int LLVMFuzzerTestOneInput(const unsigned char* data,
   // Now parse it into a tree. Note that parsing will (when asserts are enabled)
   // walk the entire tree to verify it so we don't have to do that here.
   ParseTree tree = ParseTree::Parse(tokens, NullDiagnosticConsumer());
-  if (tree.HasErrors()) {
+  if (tree.has_errors()) {
     return 0;
   }
 
   // In the absence of parse errors, we should have exactly as many nodes as
   // tokens.
-  CHECK(tree.Size() == tokens.size()) << "Unexpected number of tree nodes!";
+  CHECK(tree.size() == tokens.size()) << "Unexpected number of tree nodes!";
 
   return 0;
 }
diff --git a/toolchain/parser/parse_tree_test.cpp b/toolchain/parser/parse_tree_test.cpp
index c94fce50f349..814e37fd3bf2 100644
--- a/toolchain/parser/parse_tree_test.cpp
+++ b/toolchain/parser/parse_tree_test.cpp
@@ -51,16 +51,16 @@ class ParseTreeTest : public ::testing::Test {
 TEST_F(ParseTreeTest, Empty) {
   TokenizedBuffer tokens = GetTokenizedBuffer("");
   ParseTree tree = ParseTree::Parse(tokens, consumer);
-  EXPECT_FALSE(tree.HasErrors());
+  EXPECT_FALSE(tree.has_errors());
   EXPECT_THAT(tree, MatchParseTreeNodes({MatchFileEnd()}));
 }
 
 TEST_F(ParseTreeTest, EmptyDeclaration) {
   TokenizedBuffer tokens = GetTokenizedBuffer(";");
   ParseTree tree = ParseTree::Parse(tokens, consumer);
-  EXPECT_FALSE(tree.HasErrors());
-  auto it = tree.Postorder().begin();
-  auto end = tree.Postorder().end();
+  EXPECT_FALSE(tree.has_errors());
+  auto it = tree.postorder().begin();
+  auto end = tree.postorder().end();
   ASSERT_THAT(it, Ne(end));
   ParseTree::Node n = *it++;
   ASSERT_THAT(it, Ne(end));
@@ -69,28 +69,28 @@ TEST_F(ParseTreeTest, EmptyDeclaration) {
 
   // Directly test the main API so that we get easier to understand errors in
   // simple cases than what the custom matcher will produce.
-  EXPECT_FALSE(tree.HasErrorInNode(n));
-  EXPECT_FALSE(tree.HasErrorInNode(eof));
-  EXPECT_THAT(tree.GetNodeKind(n), Eq(ParseNodeKind::EmptyDeclaration()));
-  EXPECT_THAT(tree.GetNodeKind(eof), Eq(ParseNodeKind::FileEnd()));
+  EXPECT_FALSE(tree.node_has_error(n));
+  EXPECT_FALSE(tree.node_has_error(eof));
+  EXPECT_THAT(tree.node_kind(n), Eq(ParseNodeKind::EmptyDeclaration()));
+  EXPECT_THAT(tree.node_kind(eof), Eq(ParseNodeKind::FileEnd()));
 
-  auto t = tree.GetNodeToken(n);
+  auto t = tree.node_token(n);
   ASSERT_THAT(tokens.tokens().begin(), Ne(tokens.tokens().end()));
   EXPECT_THAT(t, Eq(*tokens.tokens().begin()));
   EXPECT_THAT(tokens.GetTokenText(t), Eq(";"));
 
-  EXPECT_THAT(tree.Children(n).begin(), Eq(tree.Children(n).end()));
-  EXPECT_THAT(tree.Children(eof).begin(), Eq(tree.Children(eof).end()));
+  EXPECT_THAT(tree.children(n).begin(), Eq(tree.children(n).end()));
+  EXPECT_THAT(tree.children(eof).begin(), Eq(tree.children(eof).end()));
 
-  EXPECT_THAT(tree.Postorder().begin(), Eq(tree.Postorder(n).begin()));
-  EXPECT_THAT(tree.Postorder(n).end(), Eq(tree.Postorder(eof).begin()));
-  EXPECT_THAT(tree.Postorder(eof).end(), Eq(tree.Postorder().end()));
+  EXPECT_THAT(tree.postorder().begin(), Eq(tree.postorder(n).begin()));
+  EXPECT_THAT(tree.postorder(n).end(), Eq(tree.postorder(eof).begin()));
+  EXPECT_THAT(tree.postorder(eof).end(), Eq(tree.postorder().end()));
 }
 
 TEST_F(ParseTreeTest, BasicFunctionDeclaration) {
   TokenizedBuffer tokens = GetTokenizedBuffer("fn F();");
   ParseTree tree = ParseTree::Parse(tokens, consumer);
-  EXPECT_FALSE(tree.HasErrors());
+  EXPECT_FALSE(tree.has_errors());
   EXPECT_THAT(tree, MatchParseTreeNodes(
                         {MatchFunctionDeclaration("fn", MatchDeclaredName("F"),
                                                   MatchParameters(),
@@ -101,14 +101,14 @@ TEST_F(ParseTreeTest, BasicFunctionDeclaration) {
 TEST_F(ParseTreeTest, NoDeclarationIntroducerOrSemi) {
   TokenizedBuffer tokens = GetTokenizedBuffer("foo bar baz");
   ParseTree tree = ParseTree::Parse(tokens, consumer);
-  EXPECT_TRUE(tree.HasErrors());
+  EXPECT_TRUE(tree.has_errors());
   EXPECT_THAT(tree, MatchParseTreeNodes({MatchFileEnd()}));
 }
 
 TEST_F(ParseTreeTest, NoDeclarationIntroducerWithSemi) {
   TokenizedBuffer tokens = GetTokenizedBuffer("foo;");
   ParseTree tree = ParseTree::Parse(tokens, consumer);
-  EXPECT_TRUE(tree.HasErrors());
+  EXPECT_TRUE(tree.has_errors());
   EXPECT_THAT(tree, MatchParseTreeNodes({MatchEmptyDeclaration(";", HasError),
                                          MatchFileEnd()}));
 }
@@ -116,7 +116,7 @@ TEST_F(ParseTreeTest, NoDeclarationIntroducerWithSemi) {
 TEST_F(ParseTreeTest, JustFunctionIntroducerAndSemi) {
   TokenizedBuffer tokens = GetTokenizedBuffer("fn;");
   ParseTree tree = ParseTree::Parse(tokens, consumer);
-  EXPECT_TRUE(tree.HasErrors());
+  EXPECT_TRUE(tree.has_errors());
   EXPECT_THAT(tree, MatchParseTreeNodes({MatchFunctionDeclaration(
                                              HasError, MatchDeclarationEnd()),
                                          MatchFileEnd()}));
@@ -125,7 +125,7 @@ TEST_F(ParseTreeTest, JustFunctionIntroducerAndSemi) {
 TEST_F(ParseTreeTest, RepeatedFunctionIntroducerAndSemi) {
   TokenizedBuffer tokens = GetTokenizedBuffer("fn fn;");
   ParseTree tree = ParseTree::Parse(tokens, consumer);
-  EXPECT_TRUE(tree.HasErrors());
+  EXPECT_TRUE(tree.has_errors());
   EXPECT_THAT(tree, MatchParseTreeNodes({MatchFunctionDeclaration(
                                              HasError, MatchDeclarationEnd()),
                                          MatchFileEnd()}));
@@ -134,7 +134,7 @@ TEST_F(ParseTreeTest, RepeatedFunctionIntroducerAndSemi) {
 TEST_F(ParseTreeTest, FunctionDeclarationWithNoSignatureOrSemi) {
   TokenizedBuffer tokens = GetTokenizedBuffer("fn foo");
   ParseTree tree = ParseTree::Parse(tokens, consumer);
-  EXPECT_TRUE(tree.HasErrors());
+  EXPECT_TRUE(tree.has_errors());
   EXPECT_THAT(tree,
               MatchParseTreeNodes(
                   {MatchFunctionDeclaration(HasError, MatchDeclaredName("foo")),
@@ -145,7 +145,7 @@ TEST_F(ParseTreeTest,
        FunctionDeclarationWithIdentifierInsteadOfSignatureAndSemi) {
   TokenizedBuffer tokens = GetTokenizedBuffer("fn foo bar;");
   ParseTree tree = ParseTree::Parse(tokens, consumer);
-  EXPECT_TRUE(tree.HasErrors());
+  EXPECT_TRUE(tree.has_errors());
   EXPECT_THAT(tree, MatchParseTreeNodes({MatchFunctionDeclaration(
                                              HasError, MatchDeclaredName("foo"),
                                              MatchDeclarationEnd()),
@@ -155,7 +155,7 @@ TEST_F(ParseTreeTest,
 TEST_F(ParseTreeTest, FunctionDeclarationWithParameterList) {
   TokenizedBuffer tokens = GetTokenizedBuffer("fn foo(bar: i32, baz: i32);");
   ParseTree tree = ParseTree::Parse(tokens, consumer);
-  EXPECT_FALSE(tree.HasErrors());
+  EXPECT_FALSE(tree.has_errors());
   EXPECT_THAT(
       tree,
       MatchParseTreeNodes(
@@ -177,7 +177,7 @@ TEST_F(ParseTreeTest, FunctionDefinitionWithParameterList) {
       "  foo(baz, bar + baz);\n"
       "}");
   ParseTree tree = ParseTree::Parse(tokens, consumer);
-  EXPECT_FALSE(tree.HasErrors());
+  EXPECT_FALSE(tree.has_errors());
   EXPECT_THAT(
       tree,
       MatchParseTreeNodes(
@@ -203,7 +203,7 @@ TEST_F(ParseTreeTest, FunctionDefinitionWithParameterList) {
 TEST_F(ParseTreeTest, FunctionDeclarationWithReturnType) {
   TokenizedBuffer tokens = GetTokenizedBuffer("fn foo() -> u32;");
   ParseTree tree = ParseTree::Parse(tokens, consumer);
-  EXPECT_FALSE(tree.HasErrors());
+  EXPECT_FALSE(tree.has_errors());
   EXPECT_THAT(
       tree,
       MatchParseTreeNodes(
@@ -219,7 +219,7 @@ TEST_F(ParseTreeTest, FunctionDefinitionWithReturnType) {
       "  return 42;\n"
       "}");
   ParseTree tree = ParseTree::Parse(tokens, consumer);
-  EXPECT_FALSE(tree.HasErrors());
+  EXPECT_FALSE(tree.has_errors());
   EXPECT_THAT(tree,
               MatchParseTreeNodes(
                   {MatchFunctionDeclaration(
@@ -236,7 +236,7 @@ TEST_F(ParseTreeTest, FunctionDeclarationWithSingleIdentifierParameterList) {
   ParseTree tree = ParseTree::Parse(tokens, consumer);
   // Note: this might become valid depending on the parameter syntax, this test
   // shouldn't be taken as a sign it should remain invalid.
-  EXPECT_TRUE(tree.HasErrors());
+  EXPECT_TRUE(tree.has_errors());
   EXPECT_THAT(tree,
               MatchParseTreeNodes(
                   {MatchFunctionDeclaration(
@@ -249,7 +249,7 @@ TEST_F(ParseTreeTest, FunctionDeclarationWithSingleIdentifierParameterList) {
 TEST_F(ParseTreeTest, FunctionDeclarationWithoutName) {
   TokenizedBuffer tokens = GetTokenizedBuffer("fn ();");
   ParseTree tree = ParseTree::Parse(tokens, consumer);
-  EXPECT_TRUE(tree.HasErrors());
+  EXPECT_TRUE(tree.has_errors());
   EXPECT_THAT(tree, MatchParseTreeNodes({MatchFunctionDeclaration(
                                              HasError, MatchDeclarationEnd()),
                                          MatchFileEnd()}));
@@ -260,7 +260,7 @@ TEST_F(ParseTreeTest,
   TokenizedBuffer tokens = GetTokenizedBuffer(
       "fn (a tokens c d e f g h i j k l m n o p q r s t u v w x y z);");
   ParseTree tree = ParseTree::Parse(tokens, consumer);
-  EXPECT_TRUE(tree.HasErrors());
+  EXPECT_TRUE(tree.has_errors());
   EXPECT_THAT(tree, MatchParseTreeNodes({MatchFunctionDeclaration(
                                              HasError, MatchDeclarationEnd()),
                                          MatchFileEnd()}));
@@ -271,7 +271,7 @@ TEST_F(ParseTreeTest, FunctionDeclarationSkipToNewlineWithoutSemi) {
       "fn ()\n"
       "fn F();");
   ParseTree tree = ParseTree::Parse(tokens, consumer);
-  EXPECT_TRUE(tree.HasErrors());
+  EXPECT_TRUE(tree.has_errors());
   EXPECT_THAT(
       tree, MatchParseTreeNodes({MatchFunctionDeclaration(HasError),
                                  MatchFunctionDeclaration(
@@ -287,7 +287,7 @@ TEST_F(ParseTreeTest, FunctionDeclarationSkipIndentedNewlineWithSemi) {
       "    z);\n"
       "fn F();");
   ParseTree tree = ParseTree::Parse(tokens, consumer);
-  EXPECT_TRUE(tree.HasErrors());
+  EXPECT_TRUE(tree.has_errors());
   EXPECT_THAT(
       tree,
       MatchParseTreeNodes(
@@ -304,7 +304,7 @@ TEST_F(ParseTreeTest, FunctionDeclarationSkipIndentedNewlineWithoutSemi) {
       "    z)\n"
       "fn F();");
   ParseTree tree = ParseTree::Parse(tokens, consumer);
-  EXPECT_TRUE(tree.HasErrors());
+  EXPECT_TRUE(tree.has_errors());
   EXPECT_THAT(
       tree, MatchParseTreeNodes({MatchFunctionDeclaration(HasError),
                                  MatchFunctionDeclaration(
@@ -320,7 +320,7 @@ TEST_F(ParseTreeTest, FunctionDeclarationSkipIndentedNewlineUntilOutdent) {
       "      z)\n"
       "fn F();");
   ParseTree tree = ParseTree::Parse(tokens, consumer);
-  EXPECT_TRUE(tree.HasErrors());
+  EXPECT_TRUE(tree.has_errors());
   EXPECT_THAT(
       tree, MatchParseTreeNodes({MatchFunctionDeclaration(HasError),
                                  MatchFunctionDeclaration(
@@ -339,7 +339,7 @@ TEST_F(ParseTreeTest, FunctionDeclarationSkipWithoutSemiToCurly) {
       "struct X { fn () }\n"
       "fn F();");
   ParseTree tree = ParseTree::Parse(tokens, consumer);
-  EXPECT_TRUE(tree.HasErrors());
+  EXPECT_TRUE(tree.has_errors());
 }
 
 TEST_F(ParseTreeTest, BasicFunctionDefinition) {
@@ -347,7 +347,7 @@ TEST_F(ParseTreeTest, BasicFunctionDefinition) {
       "fn F() {\n"
       "}");
   ParseTree tree = ParseTree::Parse(tokens, consumer);
-  EXPECT_FALSE(tree.HasErrors());
+  EXPECT_FALSE(tree.has_errors());
   EXPECT_THAT(tree, MatchParseTreeNodes(
                         {MatchFunctionDeclaration(
                              MatchDeclaredName("F"), MatchParameters(),
@@ -363,7 +363,7 @@ TEST_F(ParseTreeTest, FunctionDefinitionWithIdenifierInStatements) {
   ParseTree tree = ParseTree::Parse(tokens, consumer);
   // Note: this might become valid depending on the expression syntax. This test
   // shouldn't be taken as a sign it should remain invalid.
-  EXPECT_TRUE(tree.HasErrors());
+  EXPECT_TRUE(tree.has_errors());
   EXPECT_THAT(tree, MatchParseTreeNodes(
                         {MatchFunctionDeclaration(
                              MatchDeclaredName("F"), MatchParameters(),
@@ -378,7 +378,7 @@ TEST_F(ParseTreeTest, FunctionDefinitionWithFunctionCall) {
       "  a.b.f(c.d, (e)).g();\n"
       "}");
   ParseTree tree = ParseTree::Parse(tokens, consumer);
-  EXPECT_FALSE(tree.HasErrors());
+  EXPECT_FALSE(tree.has_errors());
 
   ExpectedNode call_to_f = MatchCallExpression(
       MatchDesignator(MatchDesignator(MatchNameReference("a"), "b"), "f"),
@@ -400,7 +400,7 @@ TEST_F(ParseTreeTest, InvalidDesignators) {
       "  a.42;\n"
       "}");
   ParseTree tree = ParseTree::Parse(tokens, consumer);
-  EXPECT_TRUE(tree.HasErrors());
+  EXPECT_TRUE(tree.has_errors());
 
   EXPECT_THAT(tree, MatchParseTreeNodes(
                         {MatchFunctionWithBody(
@@ -426,7 +426,7 @@ TEST_F(ParseTreeTest, Operators) {
       "  n = a * b + c * d = d * d << e & f - not g;\n"
       "}");
   ParseTree tree = ParseTree::Parse(tokens, consumer);
-  EXPECT_TRUE(tree.HasErrors());
+  EXPECT_TRUE(tree.has_errors());
 
   EXPECT_THAT(
       tree,
@@ -462,7 +462,7 @@ TEST_F(ParseTreeTest, OperatorsPrefixUnary) {
       "  ++++n;\n"
       "}");
   ParseTree tree = ParseTree::Parse(tokens, consumer);
-  EXPECT_FALSE(tree.HasErrors());
+  EXPECT_FALSE(tree.has_errors());
 
   EXPECT_THAT(
       tree,
@@ -478,7 +478,7 @@ TEST_F(ParseTreeTest, OperatorsPostfixUnary) {
       "  n++++;\n"
       "}");
   ParseTree tree = ParseTree::Parse(tokens, consumer);
-  EXPECT_FALSE(tree.HasErrors());
+  EXPECT_FALSE(tree.has_errors());
 
   EXPECT_THAT(
       tree,
@@ -494,7 +494,7 @@ TEST_F(ParseTreeTest, OperatorsAssociative) {
       "  a and b and c;\n"
       "}");
   ParseTree tree = ParseTree::Parse(tokens, consumer);
-  EXPECT_FALSE(tree.HasErrors());
+  EXPECT_FALSE(tree.has_errors());
 
   EXPECT_THAT(
       tree,
@@ -512,7 +512,7 @@ TEST_F(ParseTreeTest, OperatorsMissingPrecedence1) {
       "  a and b or c;\n"
       "}");
   ParseTree tree = ParseTree::Parse(tokens, consumer);
-  EXPECT_TRUE(tree.HasErrors());
+  EXPECT_TRUE(tree.has_errors());
 
   EXPECT_THAT(
       tree,
@@ -531,7 +531,7 @@ TEST_F(ParseTreeTest, OperatorsMissingPrecedence2) {
       "  a or b and c;\n"
       "}");
   ParseTree tree = ParseTree::Parse(tokens, consumer);
-  EXPECT_TRUE(tree.HasErrors());
+  EXPECT_TRUE(tree.has_errors());
 
   EXPECT_THAT(
       tree,
@@ -550,7 +550,7 @@ TEST_F(ParseTreeTest, OperatorsMissingPrecedenceForNot) {
       "  not a and not b and not c;\n"
       "}");
   ParseTree tree = ParseTree::Parse(tokens, consumer);
-  EXPECT_FALSE(tree.HasErrors());
+  EXPECT_FALSE(tree.has_errors());
 
   EXPECT_THAT(
       tree,
@@ -575,7 +575,7 @@ TEST_F(ParseTreeTest, OperatorFixity) {
       "  G(i32*, n * n);\n"
       "}");
   ParseTree tree = ParseTree::Parse(tokens, consumer);
-  EXPECT_FALSE(tree.HasErrors());
+  EXPECT_FALSE(tree.has_errors());
 
   EXPECT_THAT(
       tree,
@@ -671,7 +671,7 @@ TEST_F(ParseTreeTest, OperatorWhitespaceErrors) {
     TokenizedBuffer tokens = GetTokenizedBuffer(input);
     ErrorTrackingDiagnosticConsumer error_tracker(consumer);
     ParseTree tree = ParseTree::Parse(tokens, error_tracker);
-    EXPECT_THAT(tree.HasErrors(), Eq(kind == Failed)) << input;
+    EXPECT_THAT(tree.has_errors(), Eq(kind == Failed)) << input;
     EXPECT_THAT(error_tracker.SeenError(), Eq(kind != Valid)) << input;
   }
 }
@@ -684,7 +684,7 @@ TEST_F(ParseTreeTest, VariableDeclarations) {
       "  var s: String = \"hello\";\n"
       "}");
   ParseTree tree = ParseTree::Parse(tokens, consumer);
-  EXPECT_FALSE(tree.HasErrors());
+  EXPECT_FALSE(tree.has_errors());
 
   EXPECT_THAT(tree,
               MatchParseTreeNodes(
@@ -718,7 +718,7 @@ TEST_F(ParseTreeTest, IfNoElse) {
       "}");
   ErrorTrackingDiagnosticConsumer error_tracker(consumer);
   ParseTree tree = ParseTree::Parse(tokens, error_tracker);
-  EXPECT_FALSE(tree.HasErrors());
+  EXPECT_FALSE(tree.has_errors());
   EXPECT_FALSE(error_tracker.SeenError());
 
   EXPECT_THAT(
@@ -753,7 +753,7 @@ TEST_F(ParseTreeTest, IfNoElseUnbraced) {
   ErrorTrackingDiagnosticConsumer error_tracker(consumer);
   ParseTree tree = ParseTree::Parse(tokens, error_tracker);
   // The missing braces are invalid, but we should be able to recover.
-  EXPECT_FALSE(tree.HasErrors());
+  EXPECT_FALSE(tree.has_errors());
   EXPECT_TRUE(error_tracker.SeenError());
 
   EXPECT_THAT(
@@ -788,7 +788,7 @@ TEST_F(ParseTreeTest, IfElse) {
       "}");
   ErrorTrackingDiagnosticConsumer error_tracker(consumer);
   ParseTree tree = ParseTree::Parse(tokens, error_tracker);
-  EXPECT_FALSE(tree.HasErrors());
+  EXPECT_FALSE(tree.has_errors());
   EXPECT_FALSE(error_tracker.SeenError());
 
   EXPECT_THAT(
@@ -855,7 +855,7 @@ TEST_F(ParseTreeTest, IfElseUnbraced) {
   ErrorTrackingDiagnosticConsumer error_tracker(consumer);
   ParseTree tree = ParseTree::Parse(tokens, error_tracker);
   // The missing braces are invalid, but we should be able to recover.
-  EXPECT_FALSE(tree.HasErrors());
+  EXPECT_FALSE(tree.has_errors());
   EXPECT_TRUE(error_tracker.SeenError());
 
   EXPECT_THAT(
@@ -906,7 +906,7 @@ TEST_F(ParseTreeTest, IfError) {
       "  if (d)\n"
       "}");
   ParseTree tree = ParseTree::Parse(tokens, consumer);
-  EXPECT_TRUE(tree.HasErrors());
+  EXPECT_TRUE(tree.has_errors());
 
   EXPECT_THAT(
       tree,
@@ -939,7 +939,7 @@ TEST_F(ParseTreeTest, WhileBreakContinue) {
       "}");
   ErrorTrackingDiagnosticConsumer error_tracker(consumer);
   ParseTree tree = ParseTree::Parse(tokens, error_tracker);
-  EXPECT_FALSE(tree.HasErrors());
+  EXPECT_FALSE(tree.has_errors());
   EXPECT_FALSE(error_tracker.SeenError());
 
   EXPECT_THAT(
@@ -970,7 +970,7 @@ TEST_F(ParseTreeTest, WhileUnbraced) {
       "}");
   ErrorTrackingDiagnosticConsumer error_tracker(consumer);
   ParseTree tree = ParseTree::Parse(tokens, error_tracker);
-  EXPECT_FALSE(tree.HasErrors());
+  EXPECT_FALSE(tree.has_errors());
   EXPECT_TRUE(error_tracker.SeenError());
 
   EXPECT_THAT(
@@ -993,7 +993,7 @@ TEST_F(ParseTreeTest, Return) {
       "  return x;\n"
       "}");
   ParseTree tree = ParseTree::Parse(tokens, consumer);
-  EXPECT_FALSE(tree.HasErrors());
+  EXPECT_FALSE(tree.has_errors());
 
   EXPECT_THAT(
       tree,
@@ -1019,7 +1019,7 @@ TEST_F(ParseTreeTest, Tuples) {
     var y: ((), (), ());
   )");
   ParseTree tree = ParseTree::Parse(tokens, consumer);
-  EXPECT_FALSE(tree.HasErrors());
+  EXPECT_FALSE(tree.has_errors());
 
   auto empty_tuple = MatchTupleLiteral(MatchTupleLiteralEnd());
 
@@ -1053,7 +1053,7 @@ TEST_F(ParseTreeTest, Structs) {
     var z: {.n: i32,} = {.n = 4,};
   )");
   ParseTree tree = ParseTree::Parse(tokens, consumer);
-  EXPECT_FALSE(tree.HasErrors());
+  EXPECT_FALSE(tree.has_errors());
 
   EXPECT_THAT(
       tree,
@@ -1146,7 +1146,7 @@ TEST_F(ParseTreeTest, StructErrors) {
     Testing::MockDiagnosticConsumer consumer;
     EXPECT_CALL(consumer, HandleDiagnostic(testcase.diag_matcher));
     ParseTree tree = ParseTree::Parse(tokens, consumer);
-    EXPECT_TRUE(tree.HasErrors());
+    EXPECT_TRUE(tree.has_errors());
   }
 }
 
@@ -1166,7 +1166,7 @@ auto GetAndDropLine(llvm::StringRef& s) -> std::string {
 TEST_F(ParseTreeTest, Printing) {
   TokenizedBuffer tokens = GetTokenizedBuffer("fn F();");
   ParseTree tree = ParseTree::Parse(tokens, consumer);
-  EXPECT_FALSE(tree.HasErrors());
+  EXPECT_FALSE(tree.has_errors());
   std::string print_storage;
   llvm::raw_string_ostream print_stream(print_storage);
   tree.Print(print_stream);
@@ -1194,7 +1194,7 @@ TEST_F(ParseTreeTest, Printing) {
 TEST_F(ParseTreeTest, PrintingAsYAML) {
   TokenizedBuffer tokens = GetTokenizedBuffer("fn F();");
   ParseTree tree = ParseTree::Parse(tokens, consumer);
-  EXPECT_FALSE(tree.HasErrors());
+  EXPECT_FALSE(tree.has_errors());
   std::string print_output;
   llvm::raw_string_ostream print_stream(print_output);
   tree.Print(print_stream);
@@ -1235,7 +1235,7 @@ TEST_F(ParseTreeTest, ParenMatchRegression) {
   // the closing `}` when it skips over the nested scope.
   TokenizedBuffer tokens = GetTokenizedBuffer("var = (foo {})");
   ParseTree tree = ParseTree::Parse(tokens, consumer);
-  EXPECT_TRUE(tree.HasErrors());
+  EXPECT_TRUE(tree.has_errors());
   EXPECT_THAT(
       tree, MatchParseTreeNodes(
                 {MatchVariableDeclaration(
@@ -1263,7 +1263,7 @@ TEST_F(ParseTreeTest, RecursionLimit) {
           "Exceeded recursion limit ({0})", ParseTree::StackDepthLimit))))
       .Times(AtLeast(1));
   ParseTree tree = ParseTree::Parse(tokens, consumer);
-  EXPECT_TRUE(tree.HasErrors());
+  EXPECT_TRUE(tree.has_errors());
 }
 
 TEST_F(ParseTreeTest, ParsePostfixExpressionRegression) {
@@ -1277,7 +1277,7 @@ TEST_F(ParseTreeTest, ParsePostfixExpressionRegression) {
     TokenizedBuffer tokens = GetTokenizedBuffer(code);
     ASSERT_FALSE(tokens.has_errors());
     ParseTree tree = ParseTree::Parse(tokens, consumer);
-    EXPECT_TRUE(tree.HasErrors());
+    EXPECT_TRUE(tree.has_errors());
   }
 }
 
diff --git a/toolchain/semantics/semantics_test.cpp b/toolchain/semantics/semantics_test.cpp
index ecae3b4ad01d..8e1f89cb514f 100644
--- a/toolchain/semantics/semantics_test.cpp
+++ b/toolchain/semantics/semantics_test.cpp
@@ -34,7 +34,7 @@ class ParseTreeTest : public ::testing::Test {
 TEST_F(ParseTreeTest, Empty) {
   // TODO: Validate the returned Semantics object.
   Analyze("");
-  ASSERT_FALSE(parse_tree->HasErrors());
+  ASSERT_FALSE(parse_tree->has_errors());
 }
 
 }  // namespace