diff --git a/toolchain/check/BUILD b/toolchain/check/BUILD
index 7b50435c9280..92f03d41c523 100644
--- a/toolchain/check/BUILD
+++ b/toolchain/check/BUILD
@@ -59,6 +59,7 @@ cc_library(
         "inst_block_stack.cpp",
         "merge.cpp",
         "modifiers.cpp",
+        "name_component.cpp",
         "return.cpp",
         "subst.cpp",
     ],
@@ -75,6 +76,7 @@ cc_library(
         "keyword_modifier_set.h",
         "merge.h",
         "modifiers.h",
+        "name_component.h",
         "param_and_arg_refs_stack.h",
         "pending_block.h",
         "return.h",
diff --git a/toolchain/check/context.cpp b/toolchain/check/context.cpp
index 58fa95fc97f8..29a774d52fd1 100644
--- a/toolchain/check/context.cpp
+++ b/toolchain/check/context.cpp
@@ -626,7 +626,7 @@ auto Context::FinalizeGlobalInit() -> void {
         {.name_id = SemIR::NameId::ForIdentifier(name_id),
          .enclosing_scope_id = SemIR::NameScopeId::Package,
          .decl_id = SemIR::InstId::Invalid,
-         .implicit_param_refs_id = SemIR::InstBlockId::Empty,
+         .implicit_param_refs_id = SemIR::InstBlockId::Invalid,
          .param_refs_id = SemIR::InstBlockId::Empty,
          .return_type_id = SemIR::TypeId::Invalid,
          .return_storage_id = SemIR::InstId::Invalid,
diff --git a/toolchain/check/decl_name_stack.cpp b/toolchain/check/decl_name_stack.cpp
index 4ddf3d9bfa26..aa101613aa21 100644
--- a/toolchain/check/decl_name_stack.cpp
+++ b/toolchain/check/decl_name_stack.cpp
@@ -55,28 +55,12 @@ auto DeclNameStack::PushScopeAndStartName() -> void {
   context_->scope_stack().Push();
 }
 
-auto DeclNameStack::FinishName() -> NameContext {
+auto DeclNameStack::FinishName(const NameComponent& name) -> NameContext {
   CARBON_CHECK(decl_name_stack_.back().state != NameContext::State::Finished)
       << "Finished name twice";
-  auto [params_loc_id, params_id] =
-      context_->node_stack().PopWithNodeIdIf<Parse::NodeKind::TuplePattern>();
-  auto [implicit_params_loc_id, implicit_params_id] =
-      context_->node_stack()
-          .PopWithNodeIdIf<Parse::NodeKind::ImplicitParamList>();
-  auto [loc_id, name_id] = context_->node_stack().PopNameWithNodeId();
 
-  ApplyNameQualifier(loc_id, name_id);
-
-  if (params_id || implicit_params_id) {
-    // TODO: Say which kind of declaration we're parsing.
-    CARBON_DIAGNOSTIC(UnexpectedDeclNameParams, Error,
-                      "Declaration cannot have parameters.");
-    // Point to the lexically first parameter list in the diagnostic.
-    context_->emitter().Emit(implicit_params_id
-                                 ? static_cast<SemIRLoc>(implicit_params_loc_id)
-                                 : params_loc_id,
-                             UnexpectedDeclNameParams);
-  }
+  ApplyNameQualifierTo(decl_name_stack_.back(), name.name_loc_id, name.name_id,
+                       /*is_unqualified=*/false);
 
   NameContext result = decl_name_stack_.back();
   decl_name_stack_.back().state = NameContext::State::Finished;
@@ -194,9 +178,11 @@ auto DeclNameStack::LookupOrAddName(NameContext name_context,
   return SemIR::InstId::Invalid;
 }
 
-auto DeclNameStack::ApplyNameQualifier(SemIR::LocId loc_id,
-                                       SemIR::NameId name_id) -> void {
-  ApplyNameQualifierTo(decl_name_stack_.back(), loc_id, name_id,
+auto DeclNameStack::ApplyNameQualifier(const NameComponent& name) -> void {
+  if (name.implicit_params_id.is_valid() || name.params_id.is_valid()) {
+    context_->TODO(name.params_loc_id, "name qualifier with parameters");
+  }
+  ApplyNameQualifierTo(decl_name_stack_.back(), name.name_loc_id, name.name_id,
                        /*is_unqualified=*/false);
 }
 
diff --git a/toolchain/check/decl_name_stack.h b/toolchain/check/decl_name_stack.h
index d087f08b1b35..1b4d445351bb 100644
--- a/toolchain/check/decl_name_stack.h
+++ b/toolchain/check/decl_name_stack.h
@@ -6,6 +6,7 @@
 #define CARBON_TOOLCHAIN_CHECK_DECL_NAME_STACK_H_
 
 #include "llvm/ADT/SmallVector.h"
+#include "toolchain/check/name_component.h"
 #include "toolchain/check/scope_index.h"
 #include "toolchain/check/scope_stack.h"
 #include "toolchain/sem_ir/ids.h"
@@ -157,26 +158,23 @@ class DeclNameStack {
   // state, `FinishName` and `PopScope` must be called, in that order.
   auto PushScopeAndStartName() -> void;
 
-  // Peeks the current enclosing scope of the name on top of the stack. Note
-  // that if we're still processing the name qualifiers, this can change before
-  // the name is completed. Also, if the name up to this point was already
-  // declared and is a scope, this will be that scope, rather than the scope
-  // enclosing it.
-  auto PeekEnclosingScopeId() const -> SemIR::NameScopeId {
-    return decl_name_stack_.back().enclosing_scope_id;
-  }
+  // Creates and returns a name context corresponding to declaring an
+  // unqualified name in the current context. This is suitable for adding to
+  // name lookup in situations where a qualified name is not permitted, such as
+  // a pattern binding.
+  auto MakeUnqualifiedName(SemIR::LocId loc_id, SemIR::NameId name_id)
+      -> NameContext;
 
-  // Peeks the resolution scope index of the name on top of the stack.
-  auto PeekInitialScopeIndex() const -> ScopeIndex {
-    return decl_name_stack_.back().initial_scope_index;
-  }
+  // Applies a name component as a qualifier for the current name. This will
+  // enter the scope corresponding to the name if the name describes an existing
+  // scope, such as a namespace or a defined class.
+  auto ApplyNameQualifier(const NameComponent& name) -> void;
 
   // Finishes the current declaration name processing, returning the final
-  // context for adding the name to lookup.
-  //
-  // This also pops the final name instruction from the instruction stack,
-  // which will be applied to the declaration name if appropriate.
-  auto FinishName() -> NameContext;
+  // context for adding the name to lookup. The final name component should be
+  // popped and passed to this function, and will be added to the declaration
+  // name.
+  auto FinishName(const NameComponent& name) -> NameContext;
 
   // Finishes the current declaration name processing for an `impl`, returning
   // the final context for adding the name to lookup.
@@ -193,6 +191,20 @@ class DeclNameStack {
   // This should be called at the end of the declaration.
   auto PopScope() -> void;
 
+  // Peeks the current enclosing scope of the name on top of the stack. Note
+  // that if we're still processing the name qualifiers, this can change before
+  // the name is completed. Also, if the name up to this point was already
+  // declared and is a scope, this will be that scope, rather than the scope
+  // enclosing it.
+  auto PeekEnclosingScopeId() const -> SemIR::NameScopeId {
+    return decl_name_stack_.back().enclosing_scope_id;
+  }
+
+  // Peeks the resolution scope index of the name on top of the stack.
+  auto PeekInitialScopeIndex() const -> ScopeIndex {
+    return decl_name_stack_.back().initial_scope_index;
+  }
+
   // Temporarily remove the current declaration name and its associated scopes
   // from the stack. Can only be called once the name is finished.
   auto Suspend() -> SuspendedName;
@@ -200,18 +212,6 @@ class DeclNameStack {
   // Restore a previously suspended name.
   auto Restore(SuspendedName sus) -> void;
 
-  // Creates and returns a name context corresponding to declaring an
-  // unqualified name in the current context. This is suitable for adding to
-  // name lookup in situations where a qualified name is not permitted, such as
-  // a pattern binding.
-  auto MakeUnqualifiedName(SemIR::LocId loc_id, SemIR::NameId name_id)
-      -> NameContext;
-
-  // Applies a Name from the name stack to the top of the declaration name
-  // stack. This will enter the scope corresponding to the name if the name
-  // describes an existing scope, such as a namespace or a defined class.
-  auto ApplyNameQualifier(SemIR::LocId loc_id, SemIR::NameId name_id) -> void;
-
   // Adds a name to name lookup. Assumes duplicates are already handled.
   auto AddName(NameContext name_context, SemIR::InstId target_id) -> void;
 
diff --git a/toolchain/check/handle_alias.cpp b/toolchain/check/handle_alias.cpp
index 864dc3135a6b..9e402f3e3840 100644
--- a/toolchain/check/handle_alias.cpp
+++ b/toolchain/check/handle_alias.cpp
@@ -4,6 +4,7 @@
 
 #include "toolchain/check/context.h"
 #include "toolchain/check/modifiers.h"
+#include "toolchain/check/name_component.h"
 #include "toolchain/parse/node_ids.h"
 #include "toolchain/sem_ir/ids.h"
 #include "toolchain/sem_ir/typed_insts.h"
@@ -25,7 +26,8 @@ auto HandleAliasInitializer(Context& /*context*/,
 auto HandleAlias(Context& context, Parse::AliasId /*node_id*/) -> bool {
   auto [expr_node, expr_id] = context.node_stack().PopExprWithNodeId();
 
-  auto name_context = context.decl_name_stack().FinishName();
+  auto name_context = context.decl_name_stack().FinishName(
+      PopNameComponentWithoutParams(context, Lex::TokenKind::Alias));
 
   LimitModifiersOnDecl(context, KeywordModifierSet::Access,
                        Lex::TokenKind::Alias);
diff --git a/toolchain/check/handle_class.cpp b/toolchain/check/handle_class.cpp
index 9aaa3b623065..74afd4d3ba52 100644
--- a/toolchain/check/handle_class.cpp
+++ b/toolchain/check/handle_class.cpp
@@ -9,6 +9,7 @@
 #include "toolchain/check/eval.h"
 #include "toolchain/check/merge.h"
 #include "toolchain/check/modifiers.h"
+#include "toolchain/check/name_component.h"
 #include "toolchain/sem_ir/ids.h"
 #include "toolchain/sem_ir/typed_insts.h"
 
@@ -176,14 +177,8 @@ static auto MergeOrAddName(Context& context, Parse::AnyClassDeclId node_id,
 static auto BuildClassDecl(Context& context, Parse::AnyClassDeclId node_id,
                            bool is_definition)
     -> std::tuple<SemIR::ClassId, SemIR::InstId> {
-  auto param_refs_id =
-      context.node_stack().PopIf<Parse::NodeKind::TuplePattern>().value_or(
-          SemIR::InstBlockId::Invalid);
-  auto implicit_param_refs_id =
-      context.node_stack().PopIf<Parse::NodeKind::ImplicitParamList>().value_or(
-          SemIR::InstBlockId::Invalid);
-
-  auto name_context = context.decl_name_stack().FinishName();
+  auto name = PopNameComponent(context);
+  auto name_context = context.decl_name_stack().FinishName(name);
   context.node_stack()
       .PopAndDiscardSoloNodeId<Parse::NodeKind::ClassIntroducer>();
 
@@ -222,8 +217,8 @@ static auto BuildClassDecl(Context& context, Parse::AnyClassDeclId node_id,
   SemIR::Class class_info = {
       .name_id = name_context.name_id_for_new_inst(),
       .enclosing_scope_id = name_context.enclosing_scope_id_for_new_inst(),
-      .implicit_param_refs_id = implicit_param_refs_id,
-      .param_refs_id = param_refs_id,
+      .implicit_param_refs_id = name.implicit_params_id,
+      .param_refs_id = name.params_id,
       // `.self_type_id` depends on the ClassType, so is set below.
       .self_type_id = SemIR::TypeId::Invalid,
       .decl_id = class_decl_id,
diff --git a/toolchain/check/handle_export.cpp b/toolchain/check/handle_export.cpp
index 6d3697e9e1fa..db2c589ce208 100644
--- a/toolchain/check/handle_export.cpp
+++ b/toolchain/check/handle_export.cpp
@@ -5,6 +5,7 @@
 #include "toolchain/check/context.h"
 #include "toolchain/check/decl_name_stack.h"
 #include "toolchain/check/modifiers.h"
+#include "toolchain/check/name_component.h"
 #include "toolchain/parse/typed_nodes.h"
 #include "toolchain/sem_ir/ids.h"
 #include "toolchain/sem_ir/typed_insts.h"
@@ -20,7 +21,8 @@ auto HandleExportIntroducer(Context& context,
 }
 
 auto HandleExportDecl(Context& context, Parse::ExportDeclId node_id) -> bool {
-  auto name_context = context.decl_name_stack().FinishName();
+  auto name_context = context.decl_name_stack().FinishName(
+      PopNameComponentWithoutParams(context, Lex::TokenKind::Export));
   context.decl_name_stack().PopScope();
 
   LimitModifiersOnDecl(context, KeywordModifierSet::None,
diff --git a/toolchain/check/handle_function.cpp b/toolchain/check/handle_function.cpp
index 2012929457be..1c8521397cab 100644
--- a/toolchain/check/handle_function.cpp
+++ b/toolchain/check/handle_function.cpp
@@ -11,6 +11,7 @@
 #include "toolchain/check/interface.h"
 #include "toolchain/check/merge.h"
 #include "toolchain/check/modifiers.h"
+#include "toolchain/check/name_component.h"
 #include "toolchain/parse/tree_node_diagnostic_converter.h"
 #include "toolchain/sem_ir/builtin_function_kind.h"
 #include "toolchain/sem_ir/entry_point.h"
@@ -211,18 +212,12 @@ static auto BuildFunctionDecl(Context& context,
     return_slot = SemIR::Function::ReturnSlot::Absent;
   }
 
-  auto param_refs_id =
-      context.node_stack().PopIf<Parse::NodeKind::TuplePattern>();
-  if (!param_refs_id) {
+  auto name = PopNameComponent(context);
+  if (!name.params_id.is_valid()) {
     context.TODO(node_id, "function with positional parameters");
-    param_refs_id = SemIR::InstBlockId::Empty;
+    name.params_id = SemIR::InstBlockId::Empty;
   }
-  // TODO: Use Invalid rather than Empty if there was no implicit parameter
-  // list.
-  SemIR::InstBlockId implicit_param_refs_id =
-      context.node_stack().PopIf<Parse::NodeKind::ImplicitParamList>().value_or(
-          SemIR::InstBlockId::Empty);
-  auto name_context = context.decl_name_stack().FinishName();
+  auto name_context = context.decl_name_stack().FinishName(name);
   context.node_stack()
       .PopAndDiscardSoloNodeId<Parse::NodeKind::FunctionIntroducer>();
 
@@ -256,8 +251,8 @@ static auto BuildFunctionDecl(Context& context,
       .name_id = name_context.name_id_for_new_inst(),
       .enclosing_scope_id = name_context.enclosing_scope_id_for_new_inst(),
       .decl_id = context.AddPlaceholderInst({node_id, function_decl}),
-      .implicit_param_refs_id = implicit_param_refs_id,
-      .param_refs_id = *param_refs_id,
+      .implicit_param_refs_id = name.implicit_params_id,
+      .param_refs_id = name.params_id,
       .return_type_id = return_type_id,
       .return_storage_id = return_storage_id,
       .is_extern = is_extern,
@@ -301,9 +296,8 @@ static auto BuildFunctionDecl(Context& context,
 
   if (SemIR::IsEntryPoint(context.sem_ir(), function_decl.function_id)) {
     // TODO: Update this once valid signatures for the entry point are decided.
-    if (!context.inst_blocks()
-             .Get(function_info.implicit_param_refs_id)
-             .empty() ||
+    if (function_info.implicit_param_refs_id.is_valid() ||
+        !function_info.param_refs_id.is_valid() ||
         !context.inst_blocks().Get(function_info.param_refs_id).empty() ||
         (function_info.return_type_id.is_valid() &&
          function_info.return_type_id !=
@@ -344,9 +338,9 @@ static auto HandleFunctionDefinitionAfterSignature(
   CheckFunctionReturnType(context, function.return_storage_id, function);
 
   // Check the parameter types are complete.
-  for (auto param_id : llvm::concat<SemIR::InstId>(
-           context.inst_blocks().Get(function.implicit_param_refs_id),
-           context.inst_blocks().Get(function.param_refs_id))) {
+  for (auto param_id : llvm::concat<const SemIR::InstId>(
+           context.inst_blocks().GetOrEmpty(function.implicit_param_refs_id),
+           context.inst_blocks().GetOrEmpty(function.param_refs_id))) {
     auto param = context.insts().Get(param_id);
 
     // Find the parameter in the pattern.
@@ -464,11 +458,11 @@ static auto IsValidBuiltinDeclaration(Context& context,
   // Form the list of parameter types for the declaration.
   llvm::SmallVector<SemIR::TypeId> param_type_ids;
   auto implicit_param_refs =
-      context.inst_blocks().Get(function.implicit_param_refs_id);
-  auto param_refs = context.inst_blocks().Get(function.param_refs_id);
+      context.inst_blocks().GetOrEmpty(function.implicit_param_refs_id);
+  auto param_refs = context.inst_blocks().GetOrEmpty(function.param_refs_id);
   param_type_ids.reserve(implicit_param_refs.size() + param_refs.size());
   for (auto param_id :
-       llvm::concat<SemIR::InstId>(implicit_param_refs, param_refs)) {
+       llvm::concat<const SemIR::InstId>(implicit_param_refs, param_refs)) {
     // TODO: We also need to track whether the parameter is declared with
     // `var`.
     param_type_ids.push_back(context.insts().Get(param_id).type_id());
diff --git a/toolchain/check/handle_interface.cpp b/toolchain/check/handle_interface.cpp
index 034106b92fb7..39b780786b62 100644
--- a/toolchain/check/handle_interface.cpp
+++ b/toolchain/check/handle_interface.cpp
@@ -5,6 +5,7 @@
 #include "toolchain/check/context.h"
 #include "toolchain/check/interface.h"
 #include "toolchain/check/modifiers.h"
+#include "toolchain/check/name_component.h"
 #include "toolchain/sem_ir/typed_insts.h"
 
 namespace Carbon::Check {
@@ -25,14 +26,12 @@ auto HandleInterfaceIntroducer(Context& context,
 static auto BuildInterfaceDecl(Context& context,
                                Parse::AnyInterfaceDeclId node_id)
     -> std::tuple<SemIR::InterfaceId, SemIR::InstId> {
-  if (context.node_stack().PopIf<Parse::NodeKind::TuplePattern>()) {
-    context.TODO(node_id, "generic interface");
-  }
-  if (context.node_stack().PopIf<Parse::NodeKind::ImplicitParamList>()) {
+  auto name = PopNameComponent(context);
+  if (name.params_id.is_valid() || name.implicit_params_id.is_valid()) {
     context.TODO(node_id, "generic interface");
   }
 
-  auto name_context = context.decl_name_stack().FinishName();
+  auto name_context = context.decl_name_stack().FinishName(name);
   context.node_stack()
       .PopAndDiscardSoloNodeId<Parse::NodeKind::InterfaceIntroducer>();
 
diff --git a/toolchain/check/handle_name.cpp b/toolchain/check/handle_name.cpp
index c092506c6611..cbe801d8eed6 100644
--- a/toolchain/check/handle_name.cpp
+++ b/toolchain/check/handle_name.cpp
@@ -4,6 +4,7 @@
 
 #include "toolchain/check/context.h"
 #include "toolchain/check/member_access.h"
+#include "toolchain/check/name_component.h"
 #include "toolchain/check/pointer_dereference.h"
 #include "toolchain/lex/token_kind.h"
 #include "toolchain/sem_ir/inst.h"
@@ -125,19 +126,9 @@ auto HandleSelfValueNameExpr(Context& context,
   return HandleNameAsExpr(context, node_id, SemIR::NameId::SelfValue);
 }
 
-auto HandleNameQualifier(Context& context, Parse::NameQualifierId node_id)
+auto HandleNameQualifier(Context& context, Parse::NameQualifierId /*node_id*/)
     -> bool {
-  auto params_id = context.node_stack().PopIf<Parse::NodeKind::TuplePattern>();
-  auto implicit_params_id =
-      context.node_stack().PopIf<Parse::NodeKind::ImplicitParamList>();
-  if (params_id || implicit_params_id) {
-    // TODO: Pass the parameters into decl_name_stack.
-    context.TODO(node_id, "name qualifier with parameters");
-    return false;
-  }
-
-  auto [name_node_id, name_id] = context.node_stack().PopNameWithNodeId();
-  context.decl_name_stack().ApplyNameQualifier(name_node_id, name_id);
+  context.decl_name_stack().ApplyNameQualifier(PopNameComponent(context));
   return true;
 }
 
diff --git a/toolchain/check/handle_namespace.cpp b/toolchain/check/handle_namespace.cpp
index c21ea6967fd3..7d6d4e1218cd 100644
--- a/toolchain/check/handle_namespace.cpp
+++ b/toolchain/check/handle_namespace.cpp
@@ -5,6 +5,7 @@
 #include "toolchain/check/context.h"
 #include "toolchain/check/decl_state.h"
 #include "toolchain/check/modifiers.h"
+#include "toolchain/check/name_component.h"
 #include "toolchain/sem_ir/ids.h"
 
 namespace Carbon::Check {
@@ -18,7 +19,8 @@ auto HandleNamespaceStart(Context& context, Parse::NamespaceStartId /*node_id*/)
 }
 
 auto HandleNamespace(Context& context, Parse::NamespaceId node_id) -> bool {
-  auto name_context = context.decl_name_stack().FinishName();
+  auto name_context = context.decl_name_stack().FinishName(
+      PopNameComponentWithoutParams(context, Lex::TokenKind::Namespace));
   LimitModifiersOnDecl(context, KeywordModifierSet::None,
                        Lex::TokenKind::Namespace);
   auto namespace_inst = SemIR::Namespace{
diff --git a/toolchain/check/member_access.cpp b/toolchain/check/member_access.cpp
index d73369aac779..dec4f451fdae 100644
--- a/toolchain/check/member_access.cpp
+++ b/toolchain/check/member_access.cpp
@@ -82,7 +82,7 @@ static auto IsInstanceMethod(const SemIR::File& sem_ir,
                              SemIR::FunctionId function_id) -> bool {
   const auto& function = sem_ir.functions().Get(function_id);
   for (auto param_id :
-       sem_ir.inst_blocks().Get(function.implicit_param_refs_id)) {
+       sem_ir.inst_blocks().GetOrEmpty(function.implicit_param_refs_id)) {
     auto param =
         SemIR::Function::GetParamFromParamRefId(sem_ir, param_id).second;
     if (param.name_id == SemIR::NameId::SelfValue) {
diff --git a/toolchain/check/name_component.cpp b/toolchain/check/name_component.cpp
new file mode 100644
index 000000000000..b5c785132af8
--- /dev/null
+++ b/toolchain/check/name_component.cpp
@@ -0,0 +1,50 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+#include "toolchain/check/name_component.h"
+
+#include "toolchain/check/context.h"
+
+namespace Carbon::Check {
+
+auto PopNameComponent(Context& context) -> NameComponent {
+  auto [params_loc_id, params_id] =
+      context.node_stack().PopWithNodeIdIf<Parse::NodeKind::TuplePattern>();
+  auto [implicit_params_loc_id, implicit_params_id] =
+      context.node_stack()
+          .PopWithNodeIdIf<Parse::NodeKind::ImplicitParamList>();
+  auto [name_loc_id, name_id] = context.node_stack().PopNameWithNodeId();
+  return {
+      .name_loc_id = name_loc_id,
+      .name_id = name_id,
+      .implicit_params_loc_id = implicit_params_loc_id,
+      .implicit_params_id =
+          implicit_params_id.value_or(SemIR::InstBlockId::Invalid),
+      .params_loc_id = params_loc_id,
+      .params_id = params_id.value_or(SemIR::InstBlockId::Invalid),
+  };
+}
+
+// Pop the name of a declaration from the node stack, and diagnose if it has
+// parameters.
+auto PopNameComponentWithoutParams(Context& context, Lex::TokenKind introducer)
+    -> NameComponent {
+  NameComponent name = PopNameComponent(context);
+  if (name.implicit_params_id.is_valid() || name.params_id.is_valid()) {
+    CARBON_DIAGNOSTIC(UnexpectedDeclNameParams, Error,
+                      "`{0}` declaration cannot have parameters.",
+                      Lex::TokenKind);
+    // Point to the lexically first parameter list in the diagnostic.
+    context.emitter().Emit(name.implicit_params_id.is_valid()
+                               ? name.implicit_params_loc_id
+                               : name.params_loc_id,
+                           UnexpectedDeclNameParams, introducer);
+
+    name.implicit_params_id = SemIR::InstBlockId::Invalid;
+    name.params_id = SemIR::InstBlockId::Invalid;
+  }
+  return name;
+}
+
+}  // namespace Carbon::Check
diff --git a/toolchain/check/name_component.h b/toolchain/check/name_component.h
new file mode 100644
index 000000000000..4adecac7ce82
--- /dev/null
+++ b/toolchain/check/name_component.h
@@ -0,0 +1,42 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+#ifndef CARBON_TOOLCHAIN_CHECK_NAME_COMPONENT_H_
+#define CARBON_TOOLCHAIN_CHECK_NAME_COMPONENT_H_
+
+#include "toolchain/check/node_stack.h"
+#include "toolchain/parse/node_ids.h"
+#include "toolchain/sem_ir/ids.h"
+
+namespace Carbon::Check {
+
+class Context;
+
+// A component in a declaration name, such as `C[T:! type](N:! T)` in
+// `fn C[T:! type](N:! T).F() {}`.
+struct NameComponent {
+  // The name of the declaration.
+  Parse::NodeId name_loc_id;
+  SemIR::NameId name_id;
+
+  // The implicit parameter list.
+  Parse::NodeId implicit_params_loc_id;
+  SemIR::InstBlockId implicit_params_id;
+
+  // The explicit parameter list.
+  Parse::NodeId params_loc_id;
+  SemIR::InstBlockId params_id;
+};
+
+// Pop a name component from the node stack.
+auto PopNameComponent(Context& context) -> NameComponent;
+
+// Pop the name of a declaration from the node stack, and diagnose if it has
+// parameters.
+auto PopNameComponentWithoutParams(Context& context, Lex::TokenKind introducer)
+    -> NameComponent;
+
+}  // namespace Carbon::Check
+
+#endif  // CARBON_TOOLCHAIN_CHECK_NAME_COMPONENT_H_
diff --git a/toolchain/check/testdata/alias/no_prelude/fail_params.carbon b/toolchain/check/testdata/alias/no_prelude/fail_params.carbon
index 1cadc96aa6b8..cdc0e240aa41 100644
--- a/toolchain/check/testdata/alias/no_prelude/fail_params.carbon
+++ b/toolchain/check/testdata/alias/no_prelude/fail_params.carbon
@@ -4,7 +4,7 @@
 //
 // AUTOUPDATE
 
-// CHECK:STDERR: fail_params.carbon:[[@LINE+7]]:8: ERROR: Declaration cannot have parameters.
+// CHECK:STDERR: fail_params.carbon:[[@LINE+7]]:8: ERROR: `alias` declaration cannot have parameters.
 // CHECK:STDERR: alias A(T:! type) = T*;
 // CHECK:STDERR:        ^~~~~~~~~~
 // CHECK:STDERR:
diff --git a/toolchain/check/testdata/class/fail_todo_generic_method.carbon b/toolchain/check/testdata/class/fail_todo_generic_method.carbon
index 0a4f9e628f71..812e313fb6df 100644
--- a/toolchain/check/testdata/class/fail_todo_generic_method.carbon
+++ b/toolchain/check/testdata/class/fail_todo_generic_method.carbon
@@ -9,9 +9,9 @@ class Class(T:! type) {
   fn F[self: Self](n: T);
 }
 
-// CHECK:STDERR: fail_todo_generic_method.carbon:[[@LINE+3]]:4: ERROR: Semantics TODO: `name qualifier with parameters`.
+// CHECK:STDERR: fail_todo_generic_method.carbon:[[@LINE+3]]:9: ERROR: Semantics TODO: `name qualifier with parameters`.
 // CHECK:STDERR: fn Class(T:! type).F[self: Self](n: T) {}
-// CHECK:STDERR:    ^~~~~~~~~~~~~~~~
+// CHECK:STDERR:         ^~~~~~~~~~
 fn Class(T:! type).F[self: Self](n: T) {}
 
 // CHECK:STDOUT: --- fail_todo_generic_method.carbon
@@ -26,18 +26,39 @@ fn Class(T:! type).F[self: Self](n: T) {}
 // CHECK:STDOUT:   %F: type = fn_type @F [template]
 // CHECK:STDOUT:   %struct.2: F = struct_value () [template]
 // CHECK:STDOUT:   %.3: type = struct_type {.a: T} [symbolic]
+// CHECK:STDOUT:   %.4: type = ptr_type {.a: T} [symbolic]
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
-// CHECK:STDOUT: file {}
+// CHECK:STDOUT: file {
+// CHECK:STDOUT:   package: <namespace> = namespace [template] {
+// CHECK:STDOUT:     .Core = %Core
+// CHECK:STDOUT:     .Class = %Class.decl
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %Core: <namespace> = namespace [template] {}
+// CHECK:STDOUT:   %Class.decl: Class = class_decl @Class [template = constants.%struct.1] {
+// CHECK:STDOUT:     %T.loc7_13.1: type = param T
+// CHECK:STDOUT:     %T.loc7_13.2: type = bind_symbolic_name T 0, %T.loc7_13.1 [symbolic = constants.%T]
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %F.decl: F = fn_decl @F [template = constants.%struct.2] {
+// CHECK:STDOUT:     %T.loc15_10.1: type = param T
+// CHECK:STDOUT:     %T.loc15_10.2: type = bind_symbolic_name T 0, %T.loc15_10.1 [symbolic = constants.%T]
+// CHECK:STDOUT:     %Self.ref: type = name_ref Self, constants.%Class.2 [template = constants.%Class.2]
+// CHECK:STDOUT:     %self.loc15_22.1: Class = param self
+// CHECK:STDOUT:     @F.%self: Class = bind_name self, %self.loc15_22.1
+// CHECK:STDOUT:     %T.ref: type = name_ref T, %T.loc15_10.2 [symbolic = constants.%T]
+// CHECK:STDOUT:     %n.loc15_34.1: T = param n
+// CHECK:STDOUT:     @F.%n: T = bind_name n, %n.loc15_34.1
+// CHECK:STDOUT:   }
+// CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: class @Class {
-// CHECK:STDOUT:   %T.ref.loc8: type = name_ref T, <unexpected instref inst+3> [symbolic = constants.%T]
+// CHECK:STDOUT:   %T.ref.loc8: type = name_ref T, file.%T.loc7_13.2 [symbolic = constants.%T]
 // CHECK:STDOUT:   %.loc8: <unbound element of class Class> = field_decl a, element0 [template]
 // CHECK:STDOUT:   %F.decl: F = fn_decl @F [template = constants.%struct.2] {
 // CHECK:STDOUT:     %Self.ref: type = name_ref Self, constants.%Class.2 [template = constants.%Class.2]
 // CHECK:STDOUT:     %self.loc9_8.1: Class = param self
 // CHECK:STDOUT:     %self.loc9_8.2: Class = bind_name self, %self.loc9_8.1
-// CHECK:STDOUT:     %T.ref.loc9: type = name_ref T, <unexpected instref inst+3> [symbolic = constants.%T]
+// CHECK:STDOUT:     %T.ref.loc9: type = name_ref T, file.%T.loc7_13.2 [symbolic = constants.%T]
 // CHECK:STDOUT:     %n.loc9_20.1: T = param n
 // CHECK:STDOUT:     %n.loc9_20.2: T = bind_name n, %n.loc9_20.1
 // CHECK:STDOUT:   }
@@ -48,5 +69,8 @@ fn Class(T:! type).F[self: Self](n: T) {}
 // CHECK:STDOUT:   .F = %F.decl
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
-// CHECK:STDOUT: fn @F[@Class.%self.loc9_8.2: Class](@Class.%n.loc9_20.2: T);
+// CHECK:STDOUT: fn @F[%self: Class](%n: T) {
+// CHECK:STDOUT: !entry:
+// CHECK:STDOUT:   return
+// CHECK:STDOUT: }
 // CHECK:STDOUT:
diff --git a/toolchain/check/testdata/class/generic/fail_todo_member_out_of_line.carbon b/toolchain/check/testdata/class/generic/fail_todo_member_out_of_line.carbon
index 5bbd9cc86b8f..f360eb3ff665 100644
--- a/toolchain/check/testdata/class/generic/fail_todo_member_out_of_line.carbon
+++ b/toolchain/check/testdata/class/generic/fail_todo_member_out_of_line.carbon
@@ -8,9 +8,9 @@ class Class(T:! type) {
   fn F(n: T) -> T;
 }
 
-// CHECK:STDERR: fail_todo_member_out_of_line.carbon:[[@LINE+3]]:4: ERROR: Semantics TODO: `name qualifier with parameters`.
+// CHECK:STDERR: fail_todo_member_out_of_line.carbon:[[@LINE+3]]:9: ERROR: Semantics TODO: `name qualifier with parameters`.
 // CHECK:STDERR: fn Class(T:! type).F(n: T) -> T {
-// CHECK:STDERR:    ^~~~~~~~~~~~~~~~
+// CHECK:STDERR:         ^~~~~~~~~~
 fn Class(T:! type).F(n: T) -> T {
   return n;
 }
@@ -28,14 +28,33 @@ fn Class(T:! type).F(n: T) -> T {
 // CHECK:STDOUT:   %.2: type = struct_type {} [template]
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
-// CHECK:STDOUT: file {}
+// CHECK:STDOUT: file {
+// CHECK:STDOUT:   package: <namespace> = namespace [template] {
+// CHECK:STDOUT:     .Core = %Core
+// CHECK:STDOUT:     .Class = %Class.decl
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %Core: <namespace> = namespace [template] {}
+// CHECK:STDOUT:   %Class.decl: Class = class_decl @Class [template = constants.%struct.1] {
+// CHECK:STDOUT:     %T.loc7_13.1: type = param T
+// CHECK:STDOUT:     %T.loc7_13.2: type = bind_symbolic_name T 0, %T.loc7_13.1 [symbolic = constants.%T]
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %F.decl: F = fn_decl @F [template = constants.%struct.2] {
+// CHECK:STDOUT:     %T.loc14_10.1: type = param T
+// CHECK:STDOUT:     %T.loc14_10.2: type = bind_symbolic_name T 0, %T.loc14_10.1 [symbolic = constants.%T]
+// CHECK:STDOUT:     %T.ref.loc14_25: type = name_ref T, %T.loc14_10.2 [symbolic = constants.%T]
+// CHECK:STDOUT:     %n.loc14_22.1: T = param n
+// CHECK:STDOUT:     @F.%n: T = bind_name n, %n.loc14_22.1
+// CHECK:STDOUT:     %T.ref.loc14_31: type = name_ref T, %T.loc14_10.2 [symbolic = constants.%T]
+// CHECK:STDOUT:     @F.%return: ref T = var <return slot>
+// CHECK:STDOUT:   }
+// CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: class @Class {
 // CHECK:STDOUT:   %F.decl: F = fn_decl @F [template = constants.%struct.2] {
-// CHECK:STDOUT:     %T.ref.loc8_11: type = name_ref T, <unexpected instref inst+3> [symbolic = constants.%T]
+// CHECK:STDOUT:     %T.ref.loc8_11: type = name_ref T, file.%T.loc7_13.2 [symbolic = constants.%T]
 // CHECK:STDOUT:     %n.loc8_8.1: T = param n
 // CHECK:STDOUT:     %n.loc8_8.2: T = bind_name n, %n.loc8_8.1
-// CHECK:STDOUT:     %T.ref.loc8_17: type = name_ref T, <unexpected instref inst+3> [symbolic = constants.%T]
+// CHECK:STDOUT:     %T.ref.loc8_17: type = name_ref T, file.%T.loc7_13.2 [symbolic = constants.%T]
 // CHECK:STDOUT:     %return.var: ref T = var <return slot>
 // CHECK:STDOUT:   }
 // CHECK:STDOUT:
@@ -44,5 +63,9 @@ fn Class(T:! type).F(n: T) -> T {
 // CHECK:STDOUT:   .F = %F.decl
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
-// CHECK:STDOUT: fn @F(@Class.%n.loc8_8.2: T) -> T;
+// CHECK:STDOUT: fn @F(%n: T) -> T {
+// CHECK:STDOUT: !entry:
+// CHECK:STDOUT:   %n.ref: T = name_ref n, %n
+// CHECK:STDOUT:   return %n.ref
+// CHECK:STDOUT: }
 // CHECK:STDOUT:
diff --git a/toolchain/check/testdata/impl/fail_impl_bad_assoc_fn.carbon b/toolchain/check/testdata/impl/fail_impl_bad_assoc_fn.carbon
index eb2aab9beb7b..036a8f1718ae 100644
--- a/toolchain/check/testdata/impl/fail_impl_bad_assoc_fn.carbon
+++ b/toolchain/check/testdata/impl/fail_impl_bad_assoc_fn.carbon
@@ -61,10 +61,10 @@ class FExtraParam {
 
 class FExtraImplicitParam {
   impl as I {
-    // CHECK:STDERR: fail_impl_bad_assoc_fn.carbon:[[@LINE+7]]:5: ERROR: Redeclaration differs because of implicit parameter count of 1.
+    // CHECK:STDERR: fail_impl_bad_assoc_fn.carbon:[[@LINE+7]]:5: ERROR: Redeclaration differs because of implicit parameter list.
     // CHECK:STDERR:     fn F[self: Self]();
     // CHECK:STDERR:     ^~~~~~~~~~~~~~~~~~~
-    // CHECK:STDERR: fail_impl_bad_assoc_fn.carbon:[[@LINE-60]]:15: Previously declared with implicit parameter count of 0.
+    // CHECK:STDERR: fail_impl_bad_assoc_fn.carbon:[[@LINE-60]]:15: Previously declared without implicit parameter list.
     // CHECK:STDERR: interface I { fn F(); }
     // CHECK:STDERR:               ^~~~~~~
     // CHECK:STDERR:
@@ -103,10 +103,10 @@ class FMissingParam {
 
 class FMissingImplicitParam {
   impl as J {
-    // CHECK:STDERR: fail_impl_bad_assoc_fn.carbon:[[@LINE+7]]:5: ERROR: Redeclaration differs because of implicit parameter count of 0.
+    // CHECK:STDERR: fail_impl_bad_assoc_fn.carbon:[[@LINE+7]]:5: ERROR: Redeclaration differs because of missing implicit parameter list.
     // CHECK:STDERR:     fn F(b: bool) -> bool;
     // CHECK:STDERR:     ^~~~~~~~~~~~~~~~~~~~~~
-    // CHECK:STDERR: fail_impl_bad_assoc_fn.carbon:[[@LINE-20]]:15: Previously declared with implicit parameter count of 1.
+    // CHECK:STDERR: fail_impl_bad_assoc_fn.carbon:[[@LINE-20]]:15: Previously declared with implicit parameter list.
     // CHECK:STDERR: interface J { fn F[self: bool](b: bool) -> bool; }
     // CHECK:STDERR:               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     // CHECK:STDERR:
diff --git a/toolchain/check/testdata/interface/no_prelude/fail_todo_generic.carbon b/toolchain/check/testdata/interface/no_prelude/fail_todo_generic.carbon
index d27f11092277..3e835357735b 100644
--- a/toolchain/check/testdata/interface/no_prelude/fail_todo_generic.carbon
+++ b/toolchain/check/testdata/interface/no_prelude/fail_todo_generic.carbon
@@ -4,10 +4,6 @@
 //
 // AUTOUPDATE
 
-// CHECK:STDERR: fail_todo_generic.carbon:[[@LINE+7]]:1: ERROR: Semantics TODO: `generic interface`.
-// CHECK:STDERR: interface I[]();
-// CHECK:STDERR: ^~~~~~~~~~~~~~~~
-// CHECK:STDERR:
 // CHECK:STDERR: fail_todo_generic.carbon:[[@LINE+3]]:1: ERROR: Semantics TODO: `generic interface`.
 // CHECK:STDERR: interface I[]();
 // CHECK:STDERR: ^~~~~~~~~~~~~~~~
diff --git a/toolchain/check/testdata/namespace/fail_params.carbon b/toolchain/check/testdata/namespace/fail_params.carbon
index 9ff4406fd419..c6f9c2c8dbf8 100644
--- a/toolchain/check/testdata/namespace/fail_params.carbon
+++ b/toolchain/check/testdata/namespace/fail_params.carbon
@@ -4,7 +4,7 @@
 //
 // AUTOUPDATE
 
-// CHECK:STDERR: fail_params.carbon:[[@LINE+4]]:12: ERROR: Declaration cannot have parameters.
+// CHECK:STDERR: fail_params.carbon:[[@LINE+4]]:12: ERROR: `namespace` declaration cannot have parameters.
 // CHECK:STDERR: namespace A();
 // CHECK:STDERR:            ^~
 // CHECK:STDERR:
@@ -13,13 +13,13 @@ namespace A();
 // Parameters are ignored for error recovery.
 fn A.F() {}
 
-// CHECK:STDERR: fail_params.carbon:[[@LINE+4]]:12: ERROR: Declaration cannot have parameters.
+// CHECK:STDERR: fail_params.carbon:[[@LINE+4]]:12: ERROR: `namespace` declaration cannot have parameters.
 // CHECK:STDERR: namespace B(n: i32);
 // CHECK:STDERR:            ^~~~~~~~
 // CHECK:STDERR:
 namespace B(n: i32);
 
-// CHECK:STDERR: fail_params.carbon:[[@LINE+3]]:12: ERROR: Declaration cannot have parameters.
+// CHECK:STDERR: fail_params.carbon:[[@LINE+3]]:12: ERROR: `namespace` declaration cannot have parameters.
 // CHECK:STDERR: namespace C[T:! type](x: T);
 // CHECK:STDERR:            ^~~~~~~~~~
 namespace C[T:! type](x: T);
diff --git a/toolchain/check/testdata/packages/no_prelude/fail_export_name_params.carbon b/toolchain/check/testdata/packages/no_prelude/fail_export_name_params.carbon
index b370b1686e2c..89c31f1ce7ba 100644
--- a/toolchain/check/testdata/packages/no_prelude/fail_export_name_params.carbon
+++ b/toolchain/check/testdata/packages/no_prelude/fail_export_name_params.carbon
@@ -19,7 +19,7 @@ import library "a";
 
 export C1;
 
-// CHECK:STDERR: fail_b.carbon:[[@LINE+3]]:10: ERROR: Declaration cannot have parameters.
+// CHECK:STDERR: fail_b.carbon:[[@LINE+3]]:10: ERROR: `export` declaration cannot have parameters.
 // CHECK:STDERR: export C2(T:! type);
 // CHECK:STDERR:          ^~~~~~~~~~
 export C2(T:! type);
diff --git a/toolchain/lower/file_context.cpp b/toolchain/lower/file_context.cpp
index 865d23589826..7644b8a748ba 100644
--- a/toolchain/lower/file_context.cpp
+++ b/toolchain/lower/file_context.cpp
@@ -139,8 +139,9 @@ auto FileContext::BuildFunctionDecl(SemIR::FunctionId function_id)
 
   const bool has_return_slot = function.has_return_slot();
   auto implicit_param_refs =
-      sem_ir().inst_blocks().Get(function.implicit_param_refs_id);
-  auto param_refs = sem_ir().inst_blocks().Get(function.param_refs_id);
+      sem_ir().inst_blocks().GetOrEmpty(function.implicit_param_refs_id);
+  // TODO: Include parameters corresponding to positional parameters.
+  auto param_refs = sem_ir().inst_blocks().GetOrEmpty(function.param_refs_id);
 
   SemIR::InitRepr return_rep =
       function.return_type_id.is_valid()
@@ -245,8 +246,8 @@ auto FileContext::BuildFunctionDefinition(SemIR::FunctionId function_id)
   // function parameters that was already computed in BuildFunctionDecl.
   // We should only do that once.
   auto implicit_param_refs =
-      sem_ir().inst_blocks().Get(function.implicit_param_refs_id);
-  auto param_refs = sem_ir().inst_blocks().Get(function.param_refs_id);
+      sem_ir().inst_blocks().GetOrEmpty(function.implicit_param_refs_id);
+  auto param_refs = sem_ir().inst_blocks().GetOrEmpty(function.param_refs_id);
   int param_index = 0;
   if (has_return_slot) {
     function_lowering.SetLocal(function.return_storage_id,
diff --git a/toolchain/sem_ir/formatter.cpp b/toolchain/sem_ir/formatter.cpp
index 39be4f57fd82..8084bd1b750a 100644
--- a/toolchain/sem_ir/formatter.cpp
+++ b/toolchain/sem_ir/formatter.cpp
@@ -233,15 +233,17 @@ class Formatter {
 
     llvm::SaveAndRestore function_scope(scope_, inst_namer_.GetScopeFor(id));
 
-    if (fn.implicit_param_refs_id != InstBlockId::Empty) {
+    if (fn.implicit_param_refs_id.is_valid()) {
       out_ << "[";
       FormatParamList(fn.implicit_param_refs_id);
       out_ << "]";
     }
 
-    out_ << "(";
-    FormatParamList(fn.param_refs_id);
-    out_ << ")";
+    if (fn.param_refs_id.is_valid()) {
+      out_ << "(";
+      FormatParamList(fn.param_refs_id);
+      out_ << ")";
+    }
 
     if (fn.return_type_id.is_valid()) {
       out_ << " -> ";
diff --git a/toolchain/sem_ir/inst.h b/toolchain/sem_ir/inst.h
index a19f31d8d264..64b14ff75262 100644
--- a/toolchain/sem_ir/inst.h
+++ b/toolchain/sem_ir/inst.h
@@ -450,7 +450,7 @@ class InstBlockStore : public BlockValueStore<InstBlockId> {
 
   // Returns the contents of the specified block, or an empty array if the block
   // is empty.
-  auto GetOrEmpty(InstBlockId block_id) -> llvm::ArrayRef<InstId> {
+  auto GetOrEmpty(InstBlockId block_id) const -> llvm::ArrayRef<InstId> {
     return block_id.is_valid() ? Get(block_id) : llvm::ArrayRef<InstId>();
   }
 };