diff --git a/android/guava-tests/test/com/google/common/net/HostSpecifierTest.java b/android/guava-tests/test/com/google/common/net/HostSpecifierTest.java
index fadeff7aadf4..8112879a86d9 100644
--- a/android/guava-tests/test/com/google/common/net/HostSpecifierTest.java
+++ b/android/guava-tests/test/com/google/common/net/HostSpecifierTest.java
@@ -92,8 +92,9 @@ public void testNulls() {
   }
 
   private void assertGood(String spec) throws ParseException {
-    HostSpecifier.fromValid(spec); // Throws exception if not working correctly
-    HostSpecifier.from(spec);
+    // Throws exception if not working correctly
+    HostSpecifier unused = HostSpecifier.fromValid(spec);
+    unused = HostSpecifier.from(spec);
     assertTrue(HostSpecifier.isValid(spec));
   }
 
diff --git a/android/guava-tests/test/com/google/common/net/InternetDomainNameTest.java b/android/guava-tests/test/com/google/common/net/InternetDomainNameTest.java
index 7113fb45741a..c440ee53f509 100644
--- a/android/guava-tests/test/com/google/common/net/InternetDomainNameTest.java
+++ b/android/guava-tests/test/com/google/common/net/InternetDomainNameTest.java
@@ -232,7 +232,7 @@ public final class InternetDomainNameTest extends TestCase {
 
   public void testValid() {
     for (String name : VALID_NAME) {
-      InternetDomainName.from(name);
+      InternetDomainName unused = InternetDomainName.from(name);
     }
   }
 
@@ -392,7 +392,7 @@ public void testParentChild() {
     // These would throw an exception if leniency were not preserved during parent() and child()
     // calls.
     InternetDomainName child = parent.child(LOTS_OF_DELTAS);
-    child.child(LOTS_OF_DELTAS);
+    InternetDomainName unused = child.child(LOTS_OF_DELTAS);
   }
 
   public void testValidTopPrivateDomain() {
diff --git a/android/guava-tests/test/com/google/common/net/PercentEscaperTest.java b/android/guava-tests/test/com/google/common/net/PercentEscaperTest.java
index 8443680e7f11..e600e4c7c1af 100644
--- a/android/guava-tests/test/com/google/common/net/PercentEscaperTest.java
+++ b/android/guava-tests/test/com/google/common/net/PercentEscaperTest.java
@@ -120,16 +120,11 @@ public void testBadArguments_badchars() {
     }
   }
 
-  /**
-   * Tests that if space is a safe character you cannot also specify 'plusForSpace' (throws {@link
-   * IllegalArgumentException}).
-   */
   public void testBadArguments_plusforspace() {
-    try {
-      new PercentEscaper(" ", false);
-    } catch (IllegalArgumentException e) {
-      fail("Space can be a 'safe' character if plusForSpace is false");
-    }
+    // space can be a safe char if plusForSpace is false
+    PercentEscaper unused = new PercentEscaper(" ", false);
+
+    // space cannot be a safe char is plusForSpace is true
     String msg = "plusForSpace cannot be specified when space is a 'safe' character";
     try {
       new PercentEscaper(" ", true);
diff --git a/android/guava/src/com/google/common/net/HostAndPort.java b/android/guava/src/com/google/common/net/HostAndPort.java
index 10eea27f81a9..a27eb65ff3ba 100644
--- a/android/guava/src/com/google/common/net/HostAndPort.java
+++ b/android/guava/src/com/google/common/net/HostAndPort.java
@@ -22,6 +22,7 @@
 import com.google.common.base.CharMatcher;
 import com.google.common.base.Objects;
 import com.google.common.base.Strings;
+import com.google.errorprone.annotations.CanIgnoreReturnValue;
 import com.google.errorprone.annotations.Immutable;
 import java.io.Serializable;
 import javax.annotation.CheckForNull;
@@ -162,6 +163,7 @@ public static HostAndPort fromHost(String host) {
    * @return if parsing was successful, a populated HostAndPort object.
    * @throws IllegalArgumentException if nothing meaningful could be parsed.
    */
+  @CanIgnoreReturnValue // TODO(b/219820829): consider removing
   public static HostAndPort fromString(String hostPortString) {
     checkNotNull(hostPortString);
     String host;
@@ -272,6 +274,7 @@ public HostAndPort withDefaultPort(int defaultPort) {
    * @return {@code this}, to enable chaining of calls.
    * @throws IllegalArgumentException if bracketless IPv6 is detected.
    */
+  @CanIgnoreReturnValue
   public HostAndPort requireBracketsForIPv6() {
     checkArgument(!hasBracketlessColons, "Possible bracketless IPv6 literal: %s", host);
     return this;
diff --git a/android/guava/src/com/google/common/net/HostSpecifier.java b/android/guava/src/com/google/common/net/HostSpecifier.java
index 55e74a7a1975..c57f3d97593c 100644
--- a/android/guava/src/com/google/common/net/HostSpecifier.java
+++ b/android/guava/src/com/google/common/net/HostSpecifier.java
@@ -16,6 +16,7 @@
 
 import com.google.common.annotations.GwtIncompatible;
 import com.google.common.base.Preconditions;
+import com.google.errorprone.annotations.CanIgnoreReturnValue;
 import java.net.InetAddress;
 import java.text.ParseException;
 import javax.annotation.CheckForNull;
@@ -108,6 +109,7 @@ public static HostSpecifier fromValid(String specifier) {
    *
    * @throws ParseException if the specifier is not valid.
    */
+  @CanIgnoreReturnValue // TODO(b/219820829): consider removing
   public static HostSpecifier from(String specifier) throws ParseException {
     try {
       return fromValid(specifier);
@@ -128,7 +130,7 @@ public static HostSpecifier from(String specifier) throws ParseException {
    */
   public static boolean isValid(String specifier) {
     try {
-      fromValid(specifier);
+      HostSpecifier unused = fromValid(specifier);
       return true;
     } catch (IllegalArgumentException e) {
       return false;
diff --git a/android/guava/src/com/google/common/net/InetAddresses.java b/android/guava/src/com/google/common/net/InetAddresses.java
index aa9cda44ff02..d3e68db8ac6f 100644
--- a/android/guava/src/com/google/common/net/InetAddresses.java
+++ b/android/guava/src/com/google/common/net/InetAddresses.java
@@ -23,6 +23,7 @@
 import com.google.common.hash.Hashing;
 import com.google.common.io.ByteStreams;
 import com.google.common.primitives.Ints;
+import com.google.errorprone.annotations.CanIgnoreReturnValue;
 import java.math.BigInteger;
 import java.net.Inet4Address;
 import java.net.Inet6Address;
@@ -142,6 +143,7 @@ private static Inet4Address getInet4Address(byte[] bytes) {
    * @return {@link InetAddress} representing the argument
    * @throws IllegalArgumentException if the argument is not a valid IP string literal
    */
+  @CanIgnoreReturnValue // TODO(b/219820829): consider removing
   public static InetAddress forString(String ipString) {
     byte[] addr = ipStringToBytes(ipString);
 
diff --git a/android/guava/src/com/google/common/net/InternetDomainName.java b/android/guava/src/com/google/common/net/InternetDomainName.java
index 902683cebf58..d71a9d5c3c6c 100644
--- a/android/guava/src/com/google/common/net/InternetDomainName.java
+++ b/android/guava/src/com/google/common/net/InternetDomainName.java
@@ -25,6 +25,7 @@
 import com.google.common.base.Optional;
 import com.google.common.base.Splitter;
 import com.google.common.collect.ImmutableList;
+import com.google.errorprone.annotations.CanIgnoreReturnValue;
 import com.google.errorprone.annotations.Immutable;
 import com.google.thirdparty.publicsuffix.PublicSuffixPatterns;
 import com.google.thirdparty.publicsuffix.PublicSuffixType;
@@ -204,6 +205,7 @@ private int findSuffixOfType(Optional<PublicSuffixType> desiredType) {
    *     {@link #isValid}
    * @since 10.0 (previously named {@code fromLenient})
    */
+  @CanIgnoreReturnValue // TODO(b/219820829): consider removing
   public static InternetDomainName from(String domain) {
     return new InternetDomainName(checkNotNull(domain));
   }
@@ -582,7 +584,7 @@ public InternetDomainName child(String leftParts) {
    */
   public static boolean isValid(String name) {
     try {
-      from(name);
+      InternetDomainName unused = from(name);
       return true;
     } catch (IllegalArgumentException e) {
       return false;
diff --git a/android/guava/src/com/google/common/net/MediaType.java b/android/guava/src/com/google/common/net/MediaType.java
index 65540228bb40..a713d0b17ae5 100644
--- a/android/guava/src/com/google/common/net/MediaType.java
+++ b/android/guava/src/com/google/common/net/MediaType.java
@@ -35,6 +35,7 @@
 import com.google.common.collect.Maps;
 import com.google.common.collect.Multimap;
 import com.google.common.collect.Multimaps;
+import com.google.errorprone.annotations.CanIgnoreReturnValue;
 import com.google.errorprone.annotations.Immutable;
 import com.google.errorprone.annotations.concurrent.LazyInit;
 import java.nio.charset.Charset;
@@ -1038,6 +1039,7 @@ private static String normalizeParameterValue(String attribute, String value) {
    *
    * @throws IllegalArgumentException if the input is not parsable
    */
+  @CanIgnoreReturnValue // TODO(b/219820829): consider removing
   public static MediaType parse(String input) {
     checkNotNull(input);
     Tokenizer tokenizer = new Tokenizer(input);
@@ -1085,6 +1087,7 @@ private static final class Tokenizer {
       this.input = input;
     }
 
+    @CanIgnoreReturnValue
     String consumeTokenIfPresent(CharMatcher matcher) {
       checkState(hasMore());
       int startPosition = position;
@@ -1107,6 +1110,7 @@ char consumeCharacter(CharMatcher matcher) {
       return c;
     }
 
+    @CanIgnoreReturnValue
     char consumeCharacter(char c) {
       checkState(hasMore());
       checkState(previewChar() == c);
diff --git a/android/guava/src/com/google/common/net/package-info.java b/android/guava/src/com/google/common/net/package-info.java
index d9db26637974..d55642d9431b 100644
--- a/android/guava/src/com/google/common/net/package-info.java
+++ b/android/guava/src/com/google/common/net/package-info.java
@@ -21,7 +21,9 @@
  *
  * @author Craig Berry
  */
+@CheckReturnValue
 @ParametersAreNonnullByDefault
 package com.google.common.net;
 
+import com.google.errorprone.annotations.CheckReturnValue;
 import javax.annotation.ParametersAreNonnullByDefault;
diff --git a/guava-tests/test/com/google/common/net/HostSpecifierTest.java b/guava-tests/test/com/google/common/net/HostSpecifierTest.java
index fadeff7aadf4..8112879a86d9 100644
--- a/guava-tests/test/com/google/common/net/HostSpecifierTest.java
+++ b/guava-tests/test/com/google/common/net/HostSpecifierTest.java
@@ -92,8 +92,9 @@ public void testNulls() {
   }
 
   private void assertGood(String spec) throws ParseException {
-    HostSpecifier.fromValid(spec); // Throws exception if not working correctly
-    HostSpecifier.from(spec);
+    // Throws exception if not working correctly
+    HostSpecifier unused = HostSpecifier.fromValid(spec);
+    unused = HostSpecifier.from(spec);
     assertTrue(HostSpecifier.isValid(spec));
   }
 
diff --git a/guava-tests/test/com/google/common/net/InternetDomainNameTest.java b/guava-tests/test/com/google/common/net/InternetDomainNameTest.java
index 7113fb45741a..c440ee53f509 100644
--- a/guava-tests/test/com/google/common/net/InternetDomainNameTest.java
+++ b/guava-tests/test/com/google/common/net/InternetDomainNameTest.java
@@ -232,7 +232,7 @@ public final class InternetDomainNameTest extends TestCase {
 
   public void testValid() {
     for (String name : VALID_NAME) {
-      InternetDomainName.from(name);
+      InternetDomainName unused = InternetDomainName.from(name);
     }
   }
 
@@ -392,7 +392,7 @@ public void testParentChild() {
     // These would throw an exception if leniency were not preserved during parent() and child()
     // calls.
     InternetDomainName child = parent.child(LOTS_OF_DELTAS);
-    child.child(LOTS_OF_DELTAS);
+    InternetDomainName unused = child.child(LOTS_OF_DELTAS);
   }
 
   public void testValidTopPrivateDomain() {
diff --git a/guava-tests/test/com/google/common/net/PercentEscaperTest.java b/guava-tests/test/com/google/common/net/PercentEscaperTest.java
index 8443680e7f11..e600e4c7c1af 100644
--- a/guava-tests/test/com/google/common/net/PercentEscaperTest.java
+++ b/guava-tests/test/com/google/common/net/PercentEscaperTest.java
@@ -120,16 +120,11 @@ public void testBadArguments_badchars() {
     }
   }
 
-  /**
-   * Tests that if space is a safe character you cannot also specify 'plusForSpace' (throws {@link
-   * IllegalArgumentException}).
-   */
   public void testBadArguments_plusforspace() {
-    try {
-      new PercentEscaper(" ", false);
-    } catch (IllegalArgumentException e) {
-      fail("Space can be a 'safe' character if plusForSpace is false");
-    }
+    // space can be a safe char if plusForSpace is false
+    PercentEscaper unused = new PercentEscaper(" ", false);
+
+    // space cannot be a safe char is plusForSpace is true
     String msg = "plusForSpace cannot be specified when space is a 'safe' character";
     try {
       new PercentEscaper(" ", true);
diff --git a/guava/src/com/google/common/net/HostAndPort.java b/guava/src/com/google/common/net/HostAndPort.java
index 10eea27f81a9..a27eb65ff3ba 100644
--- a/guava/src/com/google/common/net/HostAndPort.java
+++ b/guava/src/com/google/common/net/HostAndPort.java
@@ -22,6 +22,7 @@
 import com.google.common.base.CharMatcher;
 import com.google.common.base.Objects;
 import com.google.common.base.Strings;
+import com.google.errorprone.annotations.CanIgnoreReturnValue;
 import com.google.errorprone.annotations.Immutable;
 import java.io.Serializable;
 import javax.annotation.CheckForNull;
@@ -162,6 +163,7 @@ public static HostAndPort fromHost(String host) {
    * @return if parsing was successful, a populated HostAndPort object.
    * @throws IllegalArgumentException if nothing meaningful could be parsed.
    */
+  @CanIgnoreReturnValue // TODO(b/219820829): consider removing
   public static HostAndPort fromString(String hostPortString) {
     checkNotNull(hostPortString);
     String host;
@@ -272,6 +274,7 @@ public HostAndPort withDefaultPort(int defaultPort) {
    * @return {@code this}, to enable chaining of calls.
    * @throws IllegalArgumentException if bracketless IPv6 is detected.
    */
+  @CanIgnoreReturnValue
   public HostAndPort requireBracketsForIPv6() {
     checkArgument(!hasBracketlessColons, "Possible bracketless IPv6 literal: %s", host);
     return this;
diff --git a/guava/src/com/google/common/net/HostSpecifier.java b/guava/src/com/google/common/net/HostSpecifier.java
index 55e74a7a1975..c57f3d97593c 100644
--- a/guava/src/com/google/common/net/HostSpecifier.java
+++ b/guava/src/com/google/common/net/HostSpecifier.java
@@ -16,6 +16,7 @@
 
 import com.google.common.annotations.GwtIncompatible;
 import com.google.common.base.Preconditions;
+import com.google.errorprone.annotations.CanIgnoreReturnValue;
 import java.net.InetAddress;
 import java.text.ParseException;
 import javax.annotation.CheckForNull;
@@ -108,6 +109,7 @@ public static HostSpecifier fromValid(String specifier) {
    *
    * @throws ParseException if the specifier is not valid.
    */
+  @CanIgnoreReturnValue // TODO(b/219820829): consider removing
   public static HostSpecifier from(String specifier) throws ParseException {
     try {
       return fromValid(specifier);
@@ -128,7 +130,7 @@ public static HostSpecifier from(String specifier) throws ParseException {
    */
   public static boolean isValid(String specifier) {
     try {
-      fromValid(specifier);
+      HostSpecifier unused = fromValid(specifier);
       return true;
     } catch (IllegalArgumentException e) {
       return false;
diff --git a/guava/src/com/google/common/net/InetAddresses.java b/guava/src/com/google/common/net/InetAddresses.java
index aa9cda44ff02..d3e68db8ac6f 100644
--- a/guava/src/com/google/common/net/InetAddresses.java
+++ b/guava/src/com/google/common/net/InetAddresses.java
@@ -23,6 +23,7 @@
 import com.google.common.hash.Hashing;
 import com.google.common.io.ByteStreams;
 import com.google.common.primitives.Ints;
+import com.google.errorprone.annotations.CanIgnoreReturnValue;
 import java.math.BigInteger;
 import java.net.Inet4Address;
 import java.net.Inet6Address;
@@ -142,6 +143,7 @@ private static Inet4Address getInet4Address(byte[] bytes) {
    * @return {@link InetAddress} representing the argument
    * @throws IllegalArgumentException if the argument is not a valid IP string literal
    */
+  @CanIgnoreReturnValue // TODO(b/219820829): consider removing
   public static InetAddress forString(String ipString) {
     byte[] addr = ipStringToBytes(ipString);
 
diff --git a/guava/src/com/google/common/net/InternetDomainName.java b/guava/src/com/google/common/net/InternetDomainName.java
index 902683cebf58..d71a9d5c3c6c 100644
--- a/guava/src/com/google/common/net/InternetDomainName.java
+++ b/guava/src/com/google/common/net/InternetDomainName.java
@@ -25,6 +25,7 @@
 import com.google.common.base.Optional;
 import com.google.common.base.Splitter;
 import com.google.common.collect.ImmutableList;
+import com.google.errorprone.annotations.CanIgnoreReturnValue;
 import com.google.errorprone.annotations.Immutable;
 import com.google.thirdparty.publicsuffix.PublicSuffixPatterns;
 import com.google.thirdparty.publicsuffix.PublicSuffixType;
@@ -204,6 +205,7 @@ private int findSuffixOfType(Optional<PublicSuffixType> desiredType) {
    *     {@link #isValid}
    * @since 10.0 (previously named {@code fromLenient})
    */
+  @CanIgnoreReturnValue // TODO(b/219820829): consider removing
   public static InternetDomainName from(String domain) {
     return new InternetDomainName(checkNotNull(domain));
   }
@@ -582,7 +584,7 @@ public InternetDomainName child(String leftParts) {
    */
   public static boolean isValid(String name) {
     try {
-      from(name);
+      InternetDomainName unused = from(name);
       return true;
     } catch (IllegalArgumentException e) {
       return false;
diff --git a/guava/src/com/google/common/net/MediaType.java b/guava/src/com/google/common/net/MediaType.java
index 65540228bb40..a713d0b17ae5 100644
--- a/guava/src/com/google/common/net/MediaType.java
+++ b/guava/src/com/google/common/net/MediaType.java
@@ -35,6 +35,7 @@
 import com.google.common.collect.Maps;
 import com.google.common.collect.Multimap;
 import com.google.common.collect.Multimaps;
+import com.google.errorprone.annotations.CanIgnoreReturnValue;
 import com.google.errorprone.annotations.Immutable;
 import com.google.errorprone.annotations.concurrent.LazyInit;
 import java.nio.charset.Charset;
@@ -1038,6 +1039,7 @@ private static String normalizeParameterValue(String attribute, String value) {
    *
    * @throws IllegalArgumentException if the input is not parsable
    */
+  @CanIgnoreReturnValue // TODO(b/219820829): consider removing
   public static MediaType parse(String input) {
     checkNotNull(input);
     Tokenizer tokenizer = new Tokenizer(input);
@@ -1085,6 +1087,7 @@ private static final class Tokenizer {
       this.input = input;
     }
 
+    @CanIgnoreReturnValue
     String consumeTokenIfPresent(CharMatcher matcher) {
       checkState(hasMore());
       int startPosition = position;
@@ -1107,6 +1110,7 @@ char consumeCharacter(CharMatcher matcher) {
       return c;
     }
 
+    @CanIgnoreReturnValue
     char consumeCharacter(char c) {
       checkState(hasMore());
       checkState(previewChar() == c);
diff --git a/guava/src/com/google/common/net/package-info.java b/guava/src/com/google/common/net/package-info.java
index d9db26637974..d55642d9431b 100644
--- a/guava/src/com/google/common/net/package-info.java
+++ b/guava/src/com/google/common/net/package-info.java
@@ -21,7 +21,9 @@
  *
  * @author Craig Berry
  */
+@CheckReturnValue
 @ParametersAreNonnullByDefault
 package com.google.common.net;
 
+import com.google.errorprone.annotations.CheckReturnValue;
 import javax.annotation.ParametersAreNonnullByDefault;