diff --git a/tools/aapt/ApkBuilder.h b/tools/aapt/ApkBuilder.h
index 0d7f06b1f3239..5d3abc63519f2 100644
--- a/tools/aapt/ApkBuilder.h
+++ b/tools/aapt/ApkBuilder.h
@@ -32,7 +32,7 @@ class AaptFile;
 
 class ApkBuilder : public android::RefBase {
 public:
-    ApkBuilder(const sp<WeakResourceFilter>& configFilter);
+    explicit ApkBuilder(const sp<WeakResourceFilter>& configFilter);
 
     /**
      * Tells the builder to generate a separate APK for resources that
diff --git a/tools/aapt/CacheUpdater.h b/tools/aapt/CacheUpdater.h
index 10a1bbc2f4aaa..6fa96d67e6a3c 100644
--- a/tools/aapt/CacheUpdater.h
+++ b/tools/aapt/CacheUpdater.h
@@ -51,7 +51,7 @@ private:
 class SystemCacheUpdater : public CacheUpdater {
 public:
     // Constructor to set bundle to pass to preProcessImage
-    SystemCacheUpdater (Bundle* b)
+    explicit SystemCacheUpdater (Bundle* b)
         : bundle(b) { };
 
     // Make sure all the directories along this path exist
diff --git a/tools/aapt/Command.cpp b/tools/aapt/Command.cpp
index 59da467a1cc3a..42b752d98baa9 100644
--- a/tools/aapt/Command.cpp
+++ b/tools/aapt/Command.cpp
@@ -248,7 +248,7 @@ bail:
 }
 
 static void printResolvedResourceAttribute(const ResTable& resTable, const ResXMLTree& tree,
-        uint32_t attrRes, String8 attrLabel, String8* outError)
+        uint32_t attrRes, const String8& attrLabel, String8* outError)
 {
     Res_value value;
     AaptXml::getResolvedResourceAttribute(resTable, tree, attrRes, &value, outError);
@@ -399,7 +399,7 @@ static void printUsesImpliedPermission(const String8& name, const String8& reaso
             ResTable::normalizeForOutput(reason.string()).string());
 }
 
-Vector<String8> getNfcAidCategories(AssetManager& assets, String8 xmlPath, bool offHost,
+Vector<String8> getNfcAidCategories(AssetManager& assets, const String8& xmlPath, bool offHost,
         String8 *outError = NULL)
 {
     Asset* aidAsset = assets.openNonAsset(xmlPath, Asset::ACCESS_BUFFER);
diff --git a/tools/aapt/ConfigDescription.h b/tools/aapt/ConfigDescription.h
index 4f999a2ff0c60..09430f2532faa 100644
--- a/tools/aapt/ConfigDescription.h
+++ b/tools/aapt/ConfigDescription.h
@@ -29,7 +29,7 @@ struct ConfigDescription : public android::ResTable_config {
         size = sizeof(android::ResTable_config);
     }
 
-    ConfigDescription(const android::ResTable_config&o) {
+    ConfigDescription(const android::ResTable_config&o) {  // NOLINT(implicit)
         *static_cast<android::ResTable_config*>(this) = o;
         size = sizeof(android::ResTable_config);
     }
diff --git a/tools/aapt/CrunchCache.cpp b/tools/aapt/CrunchCache.cpp
index 0d574cf127ddc..7b8a576b88d36 100644
--- a/tools/aapt/CrunchCache.cpp
+++ b/tools/aapt/CrunchCache.cpp
@@ -94,7 +94,7 @@ void CrunchCache::loadFiles()
     delete dw;
 }
 
-bool CrunchCache::needsUpdating(String8 relativePath) const
+bool CrunchCache::needsUpdating(const String8& relativePath) const
 {
     // Retrieve modification dates for this file entry under the source and
     // cache directory trees. The vectors will return a modification date of 0
diff --git a/tools/aapt/CrunchCache.h b/tools/aapt/CrunchCache.h
index be3da5c40b255..4d6a16922f259 100644
--- a/tools/aapt/CrunchCache.h
+++ b/tools/aapt/CrunchCache.h
@@ -81,7 +81,7 @@ private:
      *          // Recrunch sourceFile out to destFile.
      *
      */
-    bool needsUpdating(String8 relativePath) const;
+    bool needsUpdating(const String8& relativePath) const;
 
     // DATA MEMBERS ====================================================
 
diff --git a/tools/aapt/FileFinder.cpp b/tools/aapt/FileFinder.cpp
index 18775c06863f3..c9d0744a44637 100644
--- a/tools/aapt/FileFinder.cpp
+++ b/tools/aapt/FileFinder.cpp
@@ -77,7 +77,7 @@ bool SystemFileFinder::findFiles(String8 basePath, Vector<String8>& extensions,
     return true;
 }
 
-void SystemFileFinder::checkAndAddFile(String8 path, const struct stat* stats,
+void SystemFileFinder::checkAndAddFile(const String8& path, const struct stat* stats,
                                        Vector<String8>& extensions,
                                        KeyedVector<String8,time_t>& fileStore)
 {
diff --git a/tools/aapt/FileFinder.h b/tools/aapt/FileFinder.h
index 6974aee033a87..f405381ee275d 100644
--- a/tools/aapt/FileFinder.h
+++ b/tools/aapt/FileFinder.h
@@ -72,7 +72,7 @@ private:
      *    time as the value.
      *
      */
-    static void checkAndAddFile(String8 path, const struct stat* stats,
+    static void checkAndAddFile(const String8& path, const struct stat* stats,
                                 Vector<String8>& extensions,
                                 KeyedVector<String8,time_t>& fileStore);
 
diff --git a/tools/aapt/IndentPrinter.h b/tools/aapt/IndentPrinter.h
index 6fc94bc927b8e..bd0edcbed8ada 100644
--- a/tools/aapt/IndentPrinter.h
+++ b/tools/aapt/IndentPrinter.h
@@ -3,7 +3,7 @@
 
 class IndentPrinter {
 public:
-    IndentPrinter(FILE* stream, int indentSize=2)
+    explicit IndentPrinter(FILE* stream, int indentSize=2)
         : mStream(stream)
         , mIndentSize(indentSize)
         , mIndent(0)
diff --git a/tools/aapt/Resource.cpp b/tools/aapt/Resource.cpp
index a7878d196c158..fa59621ef26d0 100644
--- a/tools/aapt/Resource.cpp
+++ b/tools/aapt/Resource.cpp
@@ -399,7 +399,7 @@ static void collect_files(const sp<AaptDir>& dir,
     const DefaultKeyedVector<String8, sp<AaptGroup> >& groups = dir->getFiles();
     int N = groups.size();
     for (int i=0; i<N; i++) {
-        String8 leafName = groups.keyAt(i);
+        const String8& leafName = groups.keyAt(i);
         const sp<AaptGroup>& group = groups.valueAt(i);
 
         const DefaultKeyedVector<AaptGroupEntry, sp<AaptFile> >& files
@@ -422,7 +422,7 @@ static void collect_files(const sp<AaptDir>& dir,
             set->add(leafName, group);
             resources->add(resType, set);
         } else {
-            sp<ResourceTypeSet> set = resources->valueAt(index);
+            const sp<ResourceTypeSet>& set = resources->valueAt(index);
             index = set->indexOfKey(leafName);
             if (index < 0) {
                 if (kIsDebug) {
@@ -457,7 +457,7 @@ static void collect_files(const sp<AaptAssets>& ass,
     int N = dirs.size();
 
     for (int i=0; i<N; i++) {
-        sp<AaptDir> d = dirs.itemAt(i);
+        const sp<AaptDir>& d = dirs.itemAt(i);
         if (kIsDebug) {
             printf("Collecting dir #%d %p: %s, leaf %s\n", i, d.get(), d->getPath().string(),
                     d->getLeaf().string());
@@ -615,7 +615,7 @@ static bool applyFileOverlay(Bundle *bundle,
         // get the overlay resources of the requested type
         ssize_t index = overlayRes->indexOfKey(resTypeString);
         if (index >= 0) {
-            sp<ResourceTypeSet> overlaySet = overlayRes->valueAt(index);
+            const sp<ResourceTypeSet>& overlaySet = overlayRes->valueAt(index);
 
             // for each of the resources, check for a match in the previously built
             // non-overlay "baseset".
@@ -765,7 +765,7 @@ bool addTagAttribute(const sp<XMLNode>& node, const char* ns8,
     return addTagAttribute(node, ns8, attr8, value, errorOnFailedInsert, false);
 }
 
-static void fullyQualifyClassName(const String8& package, sp<XMLNode> node,
+static void fullyQualifyClassName(const String8& package, const sp<XMLNode>& node,
         const String16& attrName) {
     XMLNode::attribute_entry* attr = node->editAttribute(
             String16("http://schemas.android.com/apk/res/android"), attrName);
@@ -1350,7 +1350,7 @@ status_t buildResources(Bundle* bundle, const sp<AaptAssets>& assets, sp<ApkBuil
             ResourceDirIterator it(resources->valueAt(index), String8("values"));
             ssize_t res;
             while ((res=it.next()) == NO_ERROR) {
-                sp<AaptFile> file = it.getFile();
+                const sp<AaptFile>& file = it.getFile();
                 res = compileResourceFile(bundle, assets, file, it.getParams(), 
                                           (current!=assets), &table);
                 if (res != NO_ERROR) {
@@ -2688,7 +2688,7 @@ status_t writeResourceSymbols(Bundle* bundle, const sp<AaptAssets>& assets,
         String8 dest(bundle->getRClassDir());
 
         if (bundle->getMakePackageDirs()) {
-            String8 pkg(package);
+            const String8& pkg(package);
             const char* last = pkg.string();
             const char* s = last-1;
             do {
diff --git a/tools/aapt/ResourceFilter.h b/tools/aapt/ResourceFilter.h
index d6430c0409ccf..40d5b752000ca 100644
--- a/tools/aapt/ResourceFilter.h
+++ b/tools/aapt/ResourceFilter.h
@@ -78,7 +78,7 @@ private:
 class StrongResourceFilter : public ResourceFilter {
 public:
     StrongResourceFilter() {}
-    StrongResourceFilter(const std::set<ConfigDescription>& configs)
+    explicit StrongResourceFilter(const std::set<ConfigDescription>& configs)
         : mConfigs(configs) {}
 
     android::status_t parse(const android::String8& str);
@@ -106,7 +106,7 @@ private:
  */
 class InverseResourceFilter : public ResourceFilter {
 public:
-    InverseResourceFilter(const android::sp<ResourceFilter>& filter)
+    explicit InverseResourceFilter(const android::sp<ResourceFilter>& filter)
         : mFilter(filter) {}
 
     bool match(const android::ResTable_config& config) const {
diff --git a/tools/aapt/ResourceTable.cpp b/tools/aapt/ResourceTable.cpp
index 4d5bb312aaf16..76c59dd570687 100644
--- a/tools/aapt/ResourceTable.cpp
+++ b/tools/aapt/ResourceTable.cpp
@@ -4081,7 +4081,7 @@ status_t ResourceTable::Type::applyPublicEntryOrder()
     
     j = 0;
     for (i=0; i<N; i++) {
-        sp<ConfigList> e = origOrder.itemAt(i);
+        const sp<ConfigList>& e = origOrder.itemAt(i);
         // There will always be enough room for the remaining entries.
         while (mOrderedConfigs.itemAt(j) != NULL) {
             j++;
@@ -4203,7 +4203,7 @@ status_t ResourceTable::Package::applyPublicTypeOrder()
 
     size_t j=0;
     for (i=0; i<N; i++) {
-        sp<Type> t = origOrder.itemAt(i);
+        const sp<Type>& t = origOrder.itemAt(i);
         // There will always be enough room for the remaining types.
         while (mOrderedTypes.itemAt(j) != NULL) {
             j++;
@@ -4636,7 +4636,7 @@ status_t ResourceTable::modifyForCompat(const Bundle* bundle) {
                         c->getEntries();
                 const size_t entryCount = entries.size();
                 for (size_t ei = 0; ei < entryCount; ei++) {
-                    sp<Entry> e = entries.valueAt(ei);
+                    const sp<Entry>& e = entries.valueAt(ei);
                     if (e == NULL || e->getType() != Entry::TYPE_BAG) {
                         continue;
                     }
diff --git a/tools/aapt/StringPool.h b/tools/aapt/StringPool.h
index 4b0d920c32745..625b0bfb38323 100644
--- a/tools/aapt/StringPool.h
+++ b/tools/aapt/StringPool.h
@@ -41,7 +41,7 @@ class StringPool
 public:
     struct entry {
         entry() : offset(0) { }
-        entry(const String16& _value) : value(_value), offset(0), hasStyles(false) { }
+        explicit entry(const String16& _value) : value(_value), offset(0), hasStyles(false) { }
         entry(const entry& o) : value(o.value), offset(o.offset),
                 hasStyles(o.hasStyles), indices(o.indices),
                 configTypeName(o.configTypeName), configs(o.configs) { }
diff --git a/tools/aapt/WorkQueue.h b/tools/aapt/WorkQueue.h
index d38f05d034e9a..ab5f9691c21db 100644
--- a/tools/aapt/WorkQueue.h
+++ b/tools/aapt/WorkQueue.h
@@ -47,7 +47,7 @@ public:
     };
 
     /* Creates a work queue with the specified maximum number of work threads. */
-    WorkQueue(size_t maxThreads, bool canCallJava = true);
+    explicit WorkQueue(size_t maxThreads, bool canCallJava = true);
 
     /* Destroys the work queue.
      * Cancels pending work and waits for all remaining threads to complete.
diff --git a/tools/aapt/XMLNode.cpp b/tools/aapt/XMLNode.cpp
index 5b215daeb4945..15ec4afa52dd4 100644
--- a/tools/aapt/XMLNode.cpp
+++ b/tools/aapt/XMLNode.cpp
@@ -67,7 +67,7 @@ static const String16 RESOURCES_PREFIX_AUTO_PACKAGE(RESOURCES_AUTO_PACKAGE_NAMES
 static const String16 RESOURCES_PRV_PREFIX(RESOURCES_ROOT_PRV_NAMESPACE);
 static const String16 RESOURCES_TOOLS_NAMESPACE("http://schemas.android.com/tools");
 
-String16 getNamespaceResourcePackage(String16 appPackage, String16 namespaceUri, bool* outIsPublic)
+String16 getNamespaceResourcePackage(const String16& appPackage, const String16& namespaceUri, bool* outIsPublic)
 {
     //printf("%s starts with %s?\n", String8(namespaceUri).string(),
     //       String8(RESOURCES_PREFIX).string());
@@ -98,7 +98,7 @@ String16 getNamespaceResourcePackage(String16 appPackage, String16 namespaceUri,
 
 status_t hasSubstitutionErrors(const char* fileName,
                                ResXMLTree* inXml,
-                               String16 str16)
+                               const String16& str16)
 {
     const char16_t* str = str16.string();
     const char16_t* p = str;
diff --git a/tools/aapt/XMLNode.h b/tools/aapt/XMLNode.h
index 749bf9f59bf73..ac920186fe631 100644
--- a/tools/aapt/XMLNode.h
+++ b/tools/aapt/XMLNode.h
@@ -178,7 +178,7 @@ private:
     XMLNode(const String8& filename, const String16& s1, const String16& s2, bool isNamespace);
     
     // Creating a CDATA node.
-    XMLNode(const String8& filename);
+    explicit XMLNode(const String8& filename);
     
     status_t collect_strings(StringPool* dest, Vector<uint32_t>* outResIds,
             bool stripComments, bool stripRawValues) const;
diff --git a/tools/aapt/pseudolocalize.h b/tools/aapt/pseudolocalize.h
index 1faecd14172d6..9bb1fd8312b07 100644
--- a/tools/aapt/pseudolocalize.h
+++ b/tools/aapt/pseudolocalize.h
@@ -43,7 +43,7 @@ class PseudoMethodAccent : public PseudoMethodImpl {
 
 class Pseudolocalizer {
  public:
-  Pseudolocalizer(PseudolocalizationMethod m);
+  explicit Pseudolocalizer(PseudolocalizationMethod m);
   ~Pseudolocalizer() { if (mImpl) delete mImpl; }
   void setMethod(PseudolocalizationMethod m);
   String16 start() { return mImpl->start(); }
diff --git a/tools/aapt2/ConfigDescription.h b/tools/aapt2/ConfigDescription.h
index 5749816f51242..b1397d2e28168 100644
--- a/tools/aapt2/ConfigDescription.h
+++ b/tools/aapt2/ConfigDescription.h
@@ -51,7 +51,7 @@ struct ConfigDescription : public android::ResTable_config {
     static void applyVersionForCompatibility(ConfigDescription* config);
 
     ConfigDescription();
-    ConfigDescription(const android::ResTable_config& o);
+    ConfigDescription(const android::ResTable_config& o);  // NOLINT(implicit)
     ConfigDescription(const ConfigDescription& o);
     ConfigDescription(ConfigDescription&& o);
 
diff --git a/tools/aapt2/Resource.h b/tools/aapt2/Resource.h
index 03ca42b286d69..9126b9592faa9 100644
--- a/tools/aapt2/Resource.h
+++ b/tools/aapt2/Resource.h
@@ -98,7 +98,7 @@ struct ResourceNameRef {
     ResourceNameRef() = default;
     ResourceNameRef(const ResourceNameRef&) = default;
     ResourceNameRef(ResourceNameRef&&) = default;
-    ResourceNameRef(const ResourceName& rhs);
+    ResourceNameRef(const ResourceName& rhs);  // NOLINT(implicit)
     ResourceNameRef(const StringPiece16& p, ResourceType t, const StringPiece16& e);
     ResourceNameRef& operator=(const ResourceNameRef& rhs) = default;
     ResourceNameRef& operator=(ResourceNameRef&& rhs) = default;
@@ -124,7 +124,7 @@ struct ResourceId {
 
     ResourceId();
     ResourceId(const ResourceId& rhs);
-    ResourceId(uint32_t resId);
+    ResourceId(uint32_t resId);  // NOLINT(implicit)
     ResourceId(uint8_t p, uint8_t t, uint16_t e);
 
     bool isValid() const;
diff --git a/tools/aapt2/ResourceTable.cpp b/tools/aapt2/ResourceTable.cpp
index e700ed98365a3..f9707e41bb3d6 100644
--- a/tools/aapt2/ResourceTable.cpp
+++ b/tools/aapt2/ResourceTable.cpp
@@ -274,7 +274,7 @@ bool ResourceTable::addResource(const ResourceNameRef& name,
 }
 
 bool ResourceTable::addResource(const ResourceNameRef& name,
-                                const ResourceId resId,
+                                const ResourceId& resId,
                                 const ConfigDescription& config,
                                 const StringPiece& product,
                                 std::unique_ptr<Value> value,
@@ -325,7 +325,7 @@ bool ResourceTable::addResourceAllowMangled(const ResourceNameRef& name,
 }
 
 bool ResourceTable::addResourceAllowMangled(const ResourceNameRef& name,
-                                            const ResourceId id,
+                                            const ResourceId& id,
                                             const ConfigDescription& config,
                                             const StringPiece& product,
                                             std::unique_ptr<Value> value,
@@ -335,7 +335,7 @@ bool ResourceTable::addResourceAllowMangled(const ResourceNameRef& name,
 }
 
 bool ResourceTable::addResourceImpl(const ResourceNameRef& name,
-                                    const ResourceId resId,
+                                    const ResourceId& resId,
                                     const ConfigDescription& config,
                                     const StringPiece& product,
                                     std::unique_ptr<Value> value,
@@ -426,18 +426,18 @@ bool ResourceTable::addResourceImpl(const ResourceNameRef& name,
     return true;
 }
 
-bool ResourceTable::setSymbolState(const ResourceNameRef& name, const ResourceId resId,
+bool ResourceTable::setSymbolState(const ResourceNameRef& name, const ResourceId& resId,
                                    const Symbol& symbol, IDiagnostics* diag) {
     return setSymbolStateImpl(name, resId, symbol, kValidNameChars, diag);
 }
 
 bool ResourceTable::setSymbolStateAllowMangled(const ResourceNameRef& name,
-                                               const ResourceId resId,
+                                               const ResourceId& resId,
                                                const Symbol& symbol, IDiagnostics* diag) {
     return setSymbolStateImpl(name, resId, symbol, kValidNameMangledChars, diag);
 }
 
-bool ResourceTable::setSymbolStateImpl(const ResourceNameRef& name, const ResourceId resId,
+bool ResourceTable::setSymbolStateImpl(const ResourceNameRef& name, const ResourceId& resId,
                                        const Symbol& symbol, const char16_t* validChars,
                                        IDiagnostics* diag) {
     assert(diag && "diagnostics can't be nullptr");
diff --git a/tools/aapt2/ResourceTable.h b/tools/aapt2/ResourceTable.h
index 5690ea6fa614f..cf9e7b8bfc00d 100644
--- a/tools/aapt2/ResourceTable.h
+++ b/tools/aapt2/ResourceTable.h
@@ -103,7 +103,7 @@ public:
      */
     std::vector<std::unique_ptr<ResourceConfigValue>> values;
 
-    ResourceEntry(const StringPiece16& name) : name(name.toString()) { }
+    explicit ResourceEntry(const StringPiece16& name) : name(name.toString()) { }
 
     ResourceConfigValue* findValue(const ConfigDescription& config);
     ResourceConfigValue* findValue(const ConfigDescription& config, const StringPiece& product);
@@ -200,7 +200,7 @@ public:
                      IDiagnostics* diag);
 
     bool addResource(const ResourceNameRef& name,
-                     const ResourceId resId,
+                     const ResourceId& resId,
                      const ConfigDescription& config,
                      const StringPiece& product,
                      std::unique_ptr<Value> value,
@@ -231,19 +231,19 @@ public:
                                  IDiagnostics* diag);
 
     bool addResourceAllowMangled(const ResourceNameRef& name,
-                                 const ResourceId id,
+                                 const ResourceId& id,
                                  const ConfigDescription& config,
                                  const StringPiece& product,
                                  std::unique_ptr<Value> value,
                                  IDiagnostics* diag);
 
     bool setSymbolState(const ResourceNameRef& name,
-                        const ResourceId resId,
+                        const ResourceId& resId,
                         const Symbol& symbol,
                         IDiagnostics* diag);
 
     bool setSymbolStateAllowMangled(const ResourceNameRef& name,
-                                    const ResourceId resId,
+                                    const ResourceId& resId,
                                     const Symbol& symbol,
                                     IDiagnostics* diag);
 
@@ -294,7 +294,7 @@ private:
                               IDiagnostics* diag);
 
     bool addResourceImpl(const ResourceNameRef& name,
-                         ResourceId resId,
+                         const ResourceId& resId,
                          const ConfigDescription& config,
                          const StringPiece& product,
                          std::unique_ptr<Value> value,
@@ -303,7 +303,7 @@ private:
                          IDiagnostics* diag);
 
     bool setSymbolStateImpl(const ResourceNameRef& name,
-                            ResourceId resId,
+                            const ResourceId& resId,
                             const Symbol& symbol,
                             const char16_t* validChars,
                             IDiagnostics* diag);
diff --git a/tools/aapt2/ResourceValues.h b/tools/aapt2/ResourceValues.h
index aa1b550bdf092..9a6f1a1dff960 100644
--- a/tools/aapt2/ResourceValues.h
+++ b/tools/aapt2/ResourceValues.h
@@ -198,7 +198,7 @@ struct Id : public BaseItem<Id> {
 struct RawString : public BaseItem<RawString> {
     StringPool::Ref value;
 
-    RawString(const StringPool::Ref& ref);
+    explicit RawString(const StringPool::Ref& ref);
 
     bool equals(const Value* value) const override;
     bool flatten(android::Res_value* outValue) const override;
@@ -209,7 +209,7 @@ struct RawString : public BaseItem<RawString> {
 struct String : public BaseItem<String> {
     StringPool::Ref value;
 
-    String(const StringPool::Ref& ref);
+    explicit String(const StringPool::Ref& ref);
 
     bool equals(const Value* value) const override;
     bool flatten(android::Res_value* outValue) const override;
@@ -220,7 +220,7 @@ struct String : public BaseItem<String> {
 struct StyledString : public BaseItem<StyledString> {
     StringPool::StyleRef value;
 
-    StyledString(const StringPool::StyleRef& ref);
+    explicit StyledString(const StringPool::StyleRef& ref);
 
     bool equals(const Value* value) const override;
     bool flatten(android::Res_value* outValue) const override;
@@ -237,7 +237,7 @@ struct FileReference : public BaseItem<FileReference> {
     io::IFile* file = nullptr;
 
     FileReference() = default;
-    FileReference(const StringPool::Ref& path);
+    explicit FileReference(const StringPool::Ref& path);
 
     bool equals(const Value* value) const override;
     bool flatten(android::Res_value* outValue) const override;
@@ -252,7 +252,7 @@ struct BinaryPrimitive : public BaseItem<BinaryPrimitive> {
     android::Res_value value;
 
     BinaryPrimitive() = default;
-    BinaryPrimitive(const android::Res_value& val);
+    explicit BinaryPrimitive(const android::Res_value& val);
     BinaryPrimitive(uint8_t dataType, uint32_t data);
 
     bool equals(const Value* value) const override;
@@ -272,7 +272,7 @@ struct Attribute : public BaseValue<Attribute> {
     int32_t maxInt;
     std::vector<Symbol> symbols;
 
-    Attribute(bool w, uint32_t t = 0u);
+    explicit Attribute(bool w, uint32_t t = 0u);
 
     bool equals(const Value* value) const override;
     Attribute* clone(StringPool* newPool) const override;
diff --git a/tools/aapt2/SdkConstants.cpp b/tools/aapt2/SdkConstants.cpp
index c2a22bf2a373e..00bac05fb3b47 100644
--- a/tools/aapt2/SdkConstants.cpp
+++ b/tools/aapt2/SdkConstants.cpp
@@ -49,7 +49,7 @@ static bool lessEntryId(const std::pair<uint16_t, size_t>& p, uint16_t entryId)
     return p.first < entryId;
 }
 
-size_t findAttributeSdkLevel(ResourceId id) {
+size_t findAttributeSdkLevel(const ResourceId& id) {
     if (id.packageId() != 0x01 && id.typeId() != 0x01) {
         return 0;
     }
diff --git a/tools/aapt2/SdkConstants.h b/tools/aapt2/SdkConstants.h
index 282ed9a56f5cb..8a7e3436ed6e1 100644
--- a/tools/aapt2/SdkConstants.h
+++ b/tools/aapt2/SdkConstants.h
@@ -45,7 +45,7 @@ enum {
     SDK_MARSHMALLOW = 23,
 };
 
-size_t findAttributeSdkLevel(ResourceId id);
+size_t findAttributeSdkLevel(const ResourceId& id);
 size_t findAttributeSdkLevel(const ResourceName& name);
 
 } // namespace aapt
diff --git a/tools/aapt2/StringPool.h b/tools/aapt2/StringPool.h
index 509e3041e0819..9e1ca912796a5 100644
--- a/tools/aapt2/StringPool.h
+++ b/tools/aapt2/StringPool.h
@@ -65,7 +65,7 @@ public:
     private:
         friend class StringPool;
 
-        Ref(Entry* entry);
+        explicit Ref(Entry* entry);
 
         Entry* mEntry;
     };
@@ -88,7 +88,7 @@ public:
     private:
         friend class StringPool;
 
-        StyleRef(StyleEntry* entry);
+        explicit StyleRef(StyleEntry* entry);
 
         StyleEntry* mEntry;
     };