diff --git a/.checkstyle/checkstyle.xml b/.checkstyle/checkstyle.xml
index bf884a0..245d331 100644
--- a/.checkstyle/checkstyle.xml
+++ b/.checkstyle/checkstyle.xml
@@ -101,6 +101,7 @@
 
     <!-- https://checkstyle.org/config_imports.html#IllegalImport -->
     <module name="IllegalImport">
+      <property name="illegalClasses" value="org.jetbrains.annotations.Nullable, org.jetbrains.annotations.NotNull"/>
       <property name="illegalPkgs" value="sun, jdk, com.sun"/>
     </module>
 
diff --git a/build.gradle.kts b/build.gradle.kts
index d8da954..d938bc3 100644
--- a/build.gradle.kts
+++ b/build.gradle.kts
@@ -10,6 +10,7 @@ plugins {
 
 dependencies {
   compileOnlyApi(libs.jetbrainsAnnotations)
+  compileOnlyApi(libs.jspecify)
   testImplementation(platform(libs.junit.bom))
   testImplementation(libs.junit.api)
   testRuntimeOnly(libs.junit.engine)
diff --git a/gradle/libs.versions.toml b/gradle/libs.versions.toml
index e744a54..2ca06e0 100644
--- a/gradle/libs.versions.toml
+++ b/gradle/libs.versions.toml
@@ -8,6 +8,7 @@ junit = "5.11.4"
 
 [libraries]
 jetbrainsAnnotations = "org.jetbrains:annotations:26.0.2"
+jspecify = { module = "org.jspecify:jspecify", version = "1.0.0"}
 junit-bom = { module = "org.junit:junit-bom", version.ref = "junit" }
 junit-api = { module = "org.junit.jupiter:junit-jupiter-api" }
 junit-engine = { module = "org.junit.jupiter:junit-jupiter-engine" }
@@ -24,4 +25,4 @@ indra-crossdoc = { id = "net.kyori.indra.crossdoc", version.ref = "indra" }
 indra-licenser-spotless = { id = "net.kyori.indra.licenser.spotless", version.ref = "indra" }
 indra-publishing-sonatype = { id = "net.kyori.indra.publishing.sonatype", version.ref = "indra" }
 nexusPublish = { id = "io.github.gradle-nexus.publish-plugin", version = "2.0.0" }
-spotless = "com.diffplug.spotless:7.0.2"
\ No newline at end of file
+spotless = "com.diffplug.spotless:7.0.2"
diff --git a/src/main/java/net/kyori/option/Option.java b/src/main/java/net/kyori/option/Option.java
index 6e4c52e..c289c2e 100644
--- a/src/main/java/net/kyori/option/Option.java
+++ b/src/main/java/net/kyori/option/Option.java
@@ -25,8 +25,7 @@
 
 import net.kyori.option.value.ValueType;
 import org.jetbrains.annotations.ApiStatus;
-import org.jetbrains.annotations.NotNull;
-import org.jetbrains.annotations.Nullable;
+import org.jspecify.annotations.Nullable;
 
 /**
  * A representation of a configurable option.
@@ -80,7 +79,7 @@ static <E extends Enum<E>> Option<E> enumOption(final String id, final Class<E>
    * @return the flag id
    * @since 1.0.0
    */
-  @NotNull String id();
+  String id();
 
   /**
    * Get the type of the option value.
@@ -90,7 +89,7 @@ static <E extends Enum<E>> Option<E> enumOption(final String id, final Class<E>
    * @deprecated for removal since 1.1.0, use {@link #valueType()} instead
    */
   @Deprecated
-  default @NotNull Class<V> type() {
+  default Class<V> type() {
     return this.valueType().type();
   }
 
@@ -100,7 +99,7 @@ static <E extends Enum<E>> Option<E> enumOption(final String id, final Class<E>
    * @return the value type
    * @since 1.0.0
    */
-  @NotNull ValueType<V> valueType();
+  ValueType<V> valueType();
 
   /**
    * Get a default value for the option, if any is present.
diff --git a/src/main/java/net/kyori/option/OptionImpl.java b/src/main/java/net/kyori/option/OptionImpl.java
index 0e61017..de5bf7f 100644
--- a/src/main/java/net/kyori/option/OptionImpl.java
+++ b/src/main/java/net/kyori/option/OptionImpl.java
@@ -25,8 +25,7 @@
 
 import java.util.Objects;
 import net.kyori.option.value.ValueType;
-import org.jetbrains.annotations.NotNull;
-import org.jetbrains.annotations.Nullable;
+import org.jspecify.annotations.Nullable;
 
 final class OptionImpl<V> implements Option<V> {
 
@@ -34,19 +33,19 @@ final class OptionImpl<V> implements Option<V> {
   private final ValueType<V> type;
   private final @Nullable V defaultValue; // excluded from equality comparisons, it does not form part of the option identity
 
-  OptionImpl(final @NotNull String id, final @NotNull ValueType<V> type, final @Nullable V defaultValue) {
+  OptionImpl(final String id, final ValueType<V> type, final @Nullable V defaultValue) {
     this.id = id;
     this.type = type;
     this.defaultValue = defaultValue;
   }
 
   @Override
-  public @NotNull String id() {
+  public String id() {
     return this.id;
   }
 
   @Override
-  public @NotNull ValueType<V> valueType() {
+  public ValueType<V> valueType() {
     return this.type;
   }
 
diff --git a/src/main/java/net/kyori/option/OptionSchema.java b/src/main/java/net/kyori/option/OptionSchema.java
index a2fc186..0fc48ee 100644
--- a/src/main/java/net/kyori/option/OptionSchema.java
+++ b/src/main/java/net/kyori/option/OptionSchema.java
@@ -25,8 +25,7 @@
 
 import java.util.Set;
 import org.jetbrains.annotations.ApiStatus;
-import org.jetbrains.annotations.NotNull;
-import org.jetbrains.annotations.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import static java.util.Objects.requireNonNull;
 
@@ -45,7 +44,7 @@ public interface OptionSchema {
    * @return the global schema
    * @since 1.1.0
    */
-  static OptionSchema.@NotNull Mutable globalSchema() {
+  static OptionSchema.Mutable globalSchema() {
     return OptionSchemaImpl.Instances.GLOBAL;
   }
 
@@ -58,7 +57,7 @@ public interface OptionSchema {
    * @return the mutable child schema
    * @since 1.1.0
    */
-  static OptionSchema.@NotNull Mutable childSchema(final @NotNull OptionSchema schema) {
+  static OptionSchema.Mutable childSchema(final OptionSchema schema) {
     final OptionSchemaImpl impl;
     if (schema instanceof OptionSchemaImpl.MutableImpl) {
       impl = (OptionSchemaImpl) ((Mutable) schema).frozenView();
@@ -76,7 +75,7 @@ public interface OptionSchema {
    * @return a mutable schema
    * @since 1.1.0
    */
-  static OptionSchema.@NotNull Mutable emptySchema() {
+  static OptionSchema.Mutable emptySchema() {
     return new OptionSchemaImpl(null).new MutableImpl();
   }
 
@@ -86,7 +85,7 @@ public interface OptionSchema {
    * @return known options
    * @since 1.1.0
    */
-  @NotNull Set<Option<?>> knownOptions();
+  Set<Option<?>> knownOptions();
 
   /**
    * Return whether the provided option is known within this scheam.
@@ -95,7 +94,7 @@ public interface OptionSchema {
    * @return whether the option is known
    * @since 1.1.0
    */
-  boolean has(final @NotNull Option<?> option);
+  boolean has(final Option<?> option);
 
   /**
    * Create a builder for an unversioned option state containing only options within this schema.
@@ -103,7 +102,7 @@ public interface OptionSchema {
    * @return the builder
    * @since 1.1.0
    */
-  OptionState.@NotNull Builder stateBuilder();
+  OptionState.Builder stateBuilder();
 
   /**
    * Create a builder for a versioned option state containing only values for options within this schema.
@@ -111,7 +110,7 @@ public interface OptionSchema {
    * @return the builder
    * @since 1.1.0
    */
-  OptionState.@NotNull VersionedBuilder versionedStateBuilder();
+  OptionState.VersionedBuilder versionedStateBuilder();
 
   /**
    * Create an empty option state within this schema.
@@ -138,7 +137,7 @@ interface Mutable extends OptionSchema {
      * @return the flag instance
      * @since 1.1.0
      */
-    @NotNull Option<String> stringOption(final @NotNull String id, final @Nullable String defaultValue);
+    Option<String> stringOption(final String id, final @Nullable String defaultValue);
 
     /**
      * Create an option with a boolean value type.
@@ -150,7 +149,7 @@ interface Mutable extends OptionSchema {
      * @return the flag instance
      * @since 1.1.0
      */
-    @NotNull Option<Boolean> booleanOption(final @NotNull String id, final boolean defaultValue);
+    Option<Boolean> booleanOption(final String id, final boolean defaultValue);
 
     /**
      * Create an option with an integer value type.
@@ -162,7 +161,7 @@ interface Mutable extends OptionSchema {
      * @return the flag instance
      * @since 1.1.0
      */
-    @NotNull Option<Integer> intOption(final @NotNull String id, final int defaultValue);
+    Option<Integer> intOption(final String id, final int defaultValue);
 
     /**
      * Create an option with a double value type.
@@ -174,7 +173,7 @@ interface Mutable extends OptionSchema {
      * @return the flag instance
      * @since 1.1.0
      */
-    @NotNull Option<Double> doubleOption(final @NotNull String id, final double defaultValue);
+    Option<Double> doubleOption(final String id, final double defaultValue);
 
     /**
      * Create an option with an enum value type.
@@ -188,7 +187,7 @@ interface Mutable extends OptionSchema {
      * @return the flag instance
      * @since 1.1.0
      */
-    <E extends Enum<E>> @NotNull Option<E> enumOption(final @NotNull String id, final @NotNull Class<E> enumClazz, final @Nullable E defaultValue);
+    <E extends Enum<E>> Option<E> enumOption(final String id, final Class<E> enumClazz, final @Nullable E defaultValue);
 
     /**
      * Return a view of this schema which does not allow consumers to register new options.
@@ -198,6 +197,6 @@ interface Mutable extends OptionSchema {
      * @return the frozen view of this schema
      * @since 1.1.0
      */
-    @NotNull OptionSchema frozenView();
+    OptionSchema frozenView();
   }
 }
diff --git a/src/main/java/net/kyori/option/OptionSchemaImpl.java b/src/main/java/net/kyori/option/OptionSchemaImpl.java
index 9f82f8b..f0fbe04 100644
--- a/src/main/java/net/kyori/option/OptionSchemaImpl.java
+++ b/src/main/java/net/kyori/option/OptionSchemaImpl.java
@@ -30,8 +30,7 @@
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.ConcurrentMap;
 import net.kyori.option.value.ValueType;
-import org.jetbrains.annotations.NotNull;
-import org.jetbrains.annotations.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import static java.util.Objects.requireNonNull;
 
@@ -47,23 +46,23 @@ final class OptionSchemaImpl implements OptionSchema {
   }
 
   @Override
-  public @NotNull Set<Option<?>> knownOptions() {
+  public Set<Option<?>> knownOptions() {
     return Collections.unmodifiableSet(new HashSet<>(this.options.values()));
   }
 
   @Override
-  public boolean has(final @NotNull Option<?> option) {
+  public boolean has(final Option<?> option) {
     final Option<?> own = this.options.get(option.id());
     return own != null && own.equals(option);
   }
 
   @Override
-  public OptionState.@NotNull Builder stateBuilder() {
+  public OptionState.Builder stateBuilder() {
     return new OptionStateImpl.BuilderImpl(this);
   }
 
   @Override
-  public OptionState.@NotNull VersionedBuilder versionedStateBuilder() {
+  public OptionState.VersionedBuilder versionedStateBuilder() {
     return new OptionStateImpl.VersionedBuilderImpl(this);
   }
 
@@ -99,54 +98,54 @@ <T> Option<T> register(final String id, final ValueType<T> type, final @Nullable
     }
 
     @Override
-    public @NotNull Option<String> stringOption(final @NotNull String id, final @Nullable String defaultValue) {
+    public Option<String> stringOption(final String id, final @Nullable String defaultValue) {
       return this.register(id, ValueType.stringType(), defaultValue);
     }
 
     @Override
-    public @NotNull Option<Boolean> booleanOption(final @NotNull String id, final boolean defaultValue) {
+    public Option<Boolean> booleanOption(final String id, final boolean defaultValue) {
       return this.register(id, ValueType.booleanType(), defaultValue);
     }
 
     @Override
-    public @NotNull Option<Integer> intOption(final @NotNull String id, final int defaultValue) {
+    public Option<Integer> intOption(final String id, final int defaultValue) {
       return this.register(id, ValueType.integerType(), defaultValue);
     }
 
     @Override
-    public @NotNull Option<Double> doubleOption(final @NotNull String id, final double defaultValue) {
+    public Option<Double> doubleOption(final String id, final double defaultValue) {
       return this.register(id, ValueType.doubleType(), defaultValue);
     }
 
     @Override
-    public @NotNull <E extends Enum<E>> Option<E> enumOption(final @NotNull String id, final @NotNull Class<E> enumClazz, final @Nullable E defaultValue) {
+    public <E extends Enum<E>> Option<E> enumOption(final String id, final Class<E> enumClazz, final @Nullable E defaultValue) {
       return this.register(id, ValueType.enumType(enumClazz), defaultValue);
     }
 
     @Override
-    public @NotNull OptionSchema frozenView() {
+    public OptionSchema frozenView() {
       return OptionSchemaImpl.this;
     }
 
     // base scheam methods
 
     @Override
-    public @NotNull Set<Option<?>> knownOptions() {
+    public Set<Option<?>> knownOptions() {
       return OptionSchemaImpl.this.knownOptions();
     }
 
     @Override
-    public boolean has(final @NotNull Option<?> option) {
+    public boolean has(final Option<?> option) {
       return OptionSchemaImpl.this.has(option);
     }
 
     @Override
-    public OptionState.@NotNull Builder stateBuilder() {
+    public OptionState.Builder stateBuilder() {
       return OptionSchemaImpl.this.stateBuilder();
     }
 
     @Override
-    public OptionState.@NotNull VersionedBuilder versionedStateBuilder() {
+    public OptionState.VersionedBuilder versionedStateBuilder() {
       return OptionSchemaImpl.this.versionedStateBuilder();
     }
 
diff --git a/src/main/java/net/kyori/option/OptionState.java b/src/main/java/net/kyori/option/OptionState.java
index e0d4859..2a1cc3b 100644
--- a/src/main/java/net/kyori/option/OptionState.java
+++ b/src/main/java/net/kyori/option/OptionState.java
@@ -27,7 +27,7 @@
 import java.util.function.Consumer;
 import net.kyori.option.value.ValueSource;
 import org.jetbrains.annotations.ApiStatus;
-import org.jetbrains.annotations.NotNull;
+import org.jspecify.annotations.Nullable;
 
 /**
  * Collection of feature flags.
@@ -56,7 +56,7 @@ static OptionState emptyOptionState() {
    * @deprecated for removal since 1.1.0, create states via {@link OptionSchema#stateBuilder()} instead
    */
   @Deprecated
-  static @NotNull Builder optionState() {
+  static Builder optionState() {
     return OptionSchema.globalSchema().stateBuilder();
   }
 
@@ -68,7 +68,7 @@ static OptionState emptyOptionState() {
    * @deprecated for removal since 1.1.0, create states via {@link OptionSchema#versionedStateBuilder()} instead
    */
   @Deprecated
-  static @NotNull VersionedBuilder versionedOptionState() {
+  static VersionedBuilder versionedOptionState() {
     return OptionSchema.globalSchema().versionedStateBuilder();
   }
 
@@ -78,7 +78,7 @@ static OptionState emptyOptionState() {
    * @return the option schema
    * @since 1.1.0
    */
-  @NotNull OptionSchema schema();
+  OptionSchema schema();
 
   /**
    * Get whether this state contains a certain option at all.
@@ -87,7 +87,7 @@ static OptionState emptyOptionState() {
    * @return whether the option has been touched.
    * @since 1.0.0
    */
-  boolean has(final @NotNull Option<?> option);
+  boolean has(final Option<?> option);
 
   /**
    * Get the value set for a certain option.
@@ -97,7 +97,7 @@ static OptionState emptyOptionState() {
    * @param <V> the value type
    * @since 1.0.0
    */
-  <V> V value(final @NotNull Option<V> option);
+  <V> @Nullable V value(final Option<V> option);
 
   /**
    * A composite option set.
@@ -114,7 +114,7 @@ interface Versioned extends OptionState {
      * @return the child sets that exist
      * @since 1.0.0
      */
-    @NotNull Map<Integer, OptionState> childStates();
+    Map<Integer, OptionState> childStates();
 
     /**
      * Request a view of this option state showing only option values available at versions up to and including {@code version}.
@@ -123,7 +123,7 @@ interface Versioned extends OptionState {
      * @return a limited view of this set
      * @since 1.0.0
      */
-    @NotNull Versioned at(final int version);
+    Versioned at(final int version);
   }
 
   /**
@@ -142,7 +142,7 @@ interface Builder {
      * @param <V> the value type
      * @since 1.0.0
      */
-    <V> @NotNull Builder value(final @NotNull Option<V> option, final @NotNull V value);
+    <V> Builder value(final Option<V> option, final V value);
 
     /**
      * Apply all values from the existing option state.
@@ -151,7 +151,7 @@ interface Builder {
      * @return this builder
      * @since 1.0.0
      */
-    @NotNull Builder values(final @NotNull OptionState existing);
+    Builder values(final OptionState existing);
 
     /**
      * Set a value for all options within the {@link #schema()} where a value is provided by the {@code source}.
@@ -160,7 +160,7 @@ interface Builder {
      * @return this builder
      * @since 1.1.0
      */
-    @NotNull Builder values(final @NotNull ValueSource source);
+    Builder values(final ValueSource source);
 
     /**
      * Create a completed option state.
@@ -168,7 +168,7 @@ interface Builder {
      * @return the built state
      * @since 1.0.0
      */
-    @NotNull OptionState build();
+    OptionState build();
   }
 
   /**
@@ -186,7 +186,7 @@ interface VersionedBuilder {
      * @return this builder
      * @since 1.0.0
      */
-    @NotNull VersionedBuilder version(final int version, final @NotNull Consumer<Builder> versionBuilder);
+    VersionedBuilder version(final int version, final Consumer<Builder> versionBuilder);
 
     /**
      * Create a completed versioned option state.
@@ -194,6 +194,6 @@ interface VersionedBuilder {
      * @return the built versioned state
      * @since 1.0.0
      */
-    @NotNull Versioned build();
+    Versioned build();
   }
 }
diff --git a/src/main/java/net/kyori/option/OptionStateImpl.java b/src/main/java/net/kyori/option/OptionStateImpl.java
index 3258a31..804c6c3 100644
--- a/src/main/java/net/kyori/option/OptionStateImpl.java
+++ b/src/main/java/net/kyori/option/OptionStateImpl.java
@@ -31,8 +31,7 @@
 import java.util.TreeMap;
 import java.util.function.Consumer;
 import net.kyori.option.value.ValueSource;
-import org.jetbrains.annotations.NotNull;
-import org.jetbrains.annotations.Nullable;
+import org.jspecify.annotations.Nullable;
 
 import static java.util.Objects.requireNonNull;
 
@@ -46,17 +45,17 @@ final class OptionStateImpl implements OptionState {
   }
 
   @Override
-  public @NotNull OptionSchema schema() {
+  public OptionSchema schema() {
     return this.schema;
   }
 
   @Override
-  public boolean has(final @NotNull Option<?> option) {
+  public boolean has(final Option<?> option) {
     return this.values.containsKey(requireNonNull(option, "flag"));
   }
 
   @Override
-  public <V> V value(final @NotNull Option<V> option) {
+  public <V> @Nullable V value(final Option<V> option) {
     final V value = option.valueType().type().cast(this.values.get(requireNonNull(option, "flag")));
     return value == null ? option.defaultValue() : value;
   }
@@ -95,27 +94,27 @@ static final class VersionedImpl implements Versioned {
     }
 
     @Override
-    public @NotNull OptionSchema schema() {
+    public OptionSchema schema() {
       return this.schema;
     }
 
     @Override
-    public boolean has(final @NotNull Option<?> option) {
+    public boolean has(final Option<?> option) {
       return this.filtered.has(option);
     }
 
     @Override
-    public <V> V value(final @NotNull Option<V> option) {
+    public <V> @Nullable V value(final Option<V> option) {
       return this.filtered.value(option);
     }
 
     @Override
-    public @NotNull Map<Integer, OptionState> childStates() {
+    public Map<Integer, OptionState> childStates() {
       return Collections.unmodifiableSortedMap(this.sets.headMap(this.targetVersion + 1));
     }
 
     @Override
-    public @NotNull Versioned at(final int version) {
+    public Versioned at(final int version) {
       return new VersionedImpl(this.schema, this.sets, version, flattened(this.schema, this.sets, version));
     }
 
@@ -170,14 +169,14 @@ static final class BuilderImpl implements OptionState.Builder {
     }
 
     @Override
-    public @NotNull OptionState build() {
+    public OptionState build() {
       if (this.values.isEmpty()) return this.schema.emptyState();
 
       return new OptionStateImpl(this.schema, this.values);
     }
 
     @Override
-    public <V> @NotNull Builder value(final @NotNull Option<V> option, final @NotNull V value) {
+    public <V> Builder value(final Option<V> option, final V value) {
       if (!this.schema.has(option)) {
         throw new IllegalStateException("Option '" + option.id() + "' was not present in active schema");
       }
@@ -200,7 +199,7 @@ private void putAll(final Map<Option<?>, Object> values) {
     }
 
     @Override
-    public @NotNull Builder values(final @NotNull OptionState existing) {
+    public Builder values(final OptionState existing) {
       if (existing instanceof OptionStateImpl) {
         this.putAll(((OptionStateImpl) existing).values);
       } else if (existing instanceof VersionedImpl) {
@@ -212,7 +211,7 @@ private void putAll(final Map<Option<?>, Object> values) {
     }
 
     @Override
-    public @NotNull Builder values(final @NotNull ValueSource source) {
+    public Builder values(final ValueSource source) {
       for (final Option<?> opt : this.schema.knownOptions()) {
         final Object value = source.value(opt);
         if (value != null) {
@@ -228,12 +227,12 @@ static final class VersionedBuilderImpl implements OptionState.VersionedBuilder
     private final OptionSchema schema;
     private final Map<Integer, OptionStateImpl.BuilderImpl> builders = new TreeMap<>();
 
-    VersionedBuilderImpl(final @NotNull OptionSchema schema) {
+    VersionedBuilderImpl(final OptionSchema schema) {
       this.schema = schema;
     }
 
     @Override
-    public OptionState.@NotNull Versioned build() {
+    public OptionState.Versioned build() {
       if (this.builders.isEmpty()) {
         return new VersionedImpl(this.schema, Collections.emptySortedMap(), 0, this.schema.emptyState());
       }
@@ -247,7 +246,7 @@ static final class VersionedBuilderImpl implements OptionState.VersionedBuilder
     }
 
     @Override
-    public @NotNull VersionedBuilder version(final int version, final @NotNull Consumer<Builder> versionBuilder) {
+    public VersionedBuilder version(final int version, final Consumer<Builder> versionBuilder) {
       requireNonNull(versionBuilder, "versionBuilder")
         .accept(this.builders.computeIfAbsent(version, $ -> new OptionStateImpl.BuilderImpl(this.schema)));
       return this;
diff --git a/src/main/java/net/kyori/option/package-info.java b/src/main/java/net/kyori/option/package-info.java
index ed4360c..3ae4948 100644
--- a/src/main/java/net/kyori/option/package-info.java
+++ b/src/main/java/net/kyori/option/package-info.java
@@ -1,4 +1,5 @@
 /**
  * Runtime option system.
  */
+@org.jspecify.annotations.NullMarked
 package net.kyori.option;
diff --git a/src/main/java/net/kyori/option/value/ValueSource.java b/src/main/java/net/kyori/option/value/ValueSource.java
index 050f24c..44d5625 100644
--- a/src/main/java/net/kyori/option/value/ValueSource.java
+++ b/src/main/java/net/kyori/option/value/ValueSource.java
@@ -24,8 +24,7 @@
 package net.kyori.option.value;
 
 import net.kyori.option.Option;
-import org.jetbrains.annotations.NotNull;
-import org.jetbrains.annotations.Nullable;
+import org.jspecify.annotations.Nullable;
 
 /**
  * A source for external option values.
@@ -42,7 +41,7 @@ public interface ValueSource {
    * @return an environment variable-backed value source with no prefix
    * @since 1.1.0
    */
-  static @NotNull ValueSource environmentVariable() {
+  static ValueSource environmentVariable() {
     return environmentVariable("");
   }
 
@@ -56,7 +55,7 @@ public interface ValueSource {
    * @return an environment variable-backed value source
    * @since 1.1.0
    */
-  static @NotNull ValueSource environmentVariable(final @NotNull String prefix) {
+  static ValueSource environmentVariable(final String prefix) {
     return new ValueSources.EnvironmentVariable(prefix);
   }
 
@@ -68,7 +67,7 @@ public interface ValueSource {
    * @return a system property-backed value source with no prefix
    * @since 1.1.0
    */
-  static @NotNull ValueSource systemProperty() {
+  static ValueSource systemProperty() {
     return systemProperty("");
   }
 
@@ -82,7 +81,7 @@ public interface ValueSource {
    * @return a system property-backed value source
    * @since 1.1.0
    */
-  static @NotNull ValueSource systemProperty(final @NotNull String prefix) {
+  static ValueSource systemProperty(final String prefix) {
     return new ValueSources.SystemProperty(prefix);
   }
 
@@ -94,5 +93,5 @@ public interface ValueSource {
    * @param <T> the value type
    * @since 1.1.0
    */
-  <T> @Nullable T value(final @NotNull Option<T> option);
+  <T> @Nullable T value(final Option<T> option);
 }
diff --git a/src/main/java/net/kyori/option/value/ValueSources.java b/src/main/java/net/kyori/option/value/ValueSources.java
index 2643bbf..b05ada6 100644
--- a/src/main/java/net/kyori/option/value/ValueSources.java
+++ b/src/main/java/net/kyori/option/value/ValueSources.java
@@ -27,8 +27,7 @@
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 import net.kyori.option.Option;
-import org.jetbrains.annotations.NotNull;
-import org.jetbrains.annotations.Nullable;
+import org.jspecify.annotations.Nullable;
 
 final class ValueSources {
   static final ValueSource ENVIRONMENT = new EnvironmentVariable("");
@@ -48,7 +47,7 @@ static final class EnvironmentVariable implements ValueSource {
     }
 
     @Override
-    public <T> @Nullable T value(final @NotNull Option<T> option) {
+    public <T> @Nullable T value(final Option<T> option) {
       final StringBuffer buf = new StringBuffer(option.id().length() + this.prefix.length());
       buf.append(this.prefix);
       final Matcher match = ENVIRONMENT_SUBST_PATTERN.matcher(option.id());
@@ -77,7 +76,7 @@ static final class SystemProperty implements ValueSource {
     }
 
     @Override
-    public <T> @Nullable T value(final @NotNull Option<T> option) {
+    public <T> @Nullable T value(final Option<T> option) {
       final StringBuffer buf = new StringBuffer(option.id().length() + this.prefix.length());
       buf.append(this.prefix);
       final Matcher match = SYSTEM_PROP_SUBST_PATTERN.matcher(option.id());
diff --git a/src/main/java/net/kyori/option/value/ValueType.java b/src/main/java/net/kyori/option/value/ValueType.java
index ad1cf68..5a4a7ff 100644
--- a/src/main/java/net/kyori/option/value/ValueType.java
+++ b/src/main/java/net/kyori/option/value/ValueType.java
@@ -23,8 +23,6 @@
  */
 package net.kyori.option.value;
 
-import org.jetbrains.annotations.NotNull;
-
 import static java.util.Objects.requireNonNull;
 
 /**
@@ -40,7 +38,7 @@ public interface ValueType<T> {
    * @return a value type for string values
    * @since 1.1.0
    */
-  static @NotNull ValueType<String> stringType() {
+  static ValueType<String> stringType() {
     return ValueTypeImpl.Types.STRING;
   }
 
@@ -50,7 +48,7 @@ public interface ValueType<T> {
    * @return a value type for boolean values
    * @since 1.1.0
    */
-  static @NotNull ValueType<Boolean> booleanType() {
+  static ValueType<Boolean> booleanType() {
     return ValueTypeImpl.Types.BOOLEAN;
   }
 
@@ -60,7 +58,7 @@ public interface ValueType<T> {
    * @return a value type for integer values
    * @since 1.1.0
    */
-  static @NotNull ValueType<Integer> integerType() {
+  static ValueType<Integer> integerType() {
     return ValueTypeImpl.Types.INT;
   }
 
@@ -70,7 +68,7 @@ public interface ValueType<T> {
    * @return a value type for double values
    * @since 1.1.0
    */
-  static @NotNull ValueType<Double> doubleType() {
+  static ValueType<Double> doubleType() {
     return ValueTypeImpl.Types.DOUBLE;
   }
 
@@ -82,7 +80,7 @@ public interface ValueType<T> {
    * @return a value type for enum values
    * @since 1.1.0
    */
-  static <E extends Enum<E>> @NotNull ValueType<E> enumType(final @NotNull Class<E> enumClazz) {
+  static <E extends Enum<E>> ValueType<E> enumType(final Class<E> enumClazz) {
     return new ValueTypeImpl.EnumType<>(requireNonNull(enumClazz, "enumClazz"));
   }
 
@@ -92,7 +90,7 @@ public interface ValueType<T> {
    * @return the object type of the value
    * @since 1.1.0
    */
-  @NotNull Class<T> type();
+  Class<T> type();
 
   /**
    * Extract a value of this type from a plain string.
@@ -102,5 +100,5 @@ public interface ValueType<T> {
    * @throws IllegalArgumentException if the value is not of an appropriate type
    * @since 1.1.0
    */
-  @NotNull T parse(final @NotNull String plainValue) throws IllegalArgumentException;
+  T parse(final String plainValue) throws IllegalArgumentException;
 }
diff --git a/src/main/java/net/kyori/option/value/ValueTypeImpl.java b/src/main/java/net/kyori/option/value/ValueTypeImpl.java
index b82799f..f11e9de 100644
--- a/src/main/java/net/kyori/option/value/ValueTypeImpl.java
+++ b/src/main/java/net/kyori/option/value/ValueTypeImpl.java
@@ -26,18 +26,17 @@
 import java.util.HashMap;
 import java.util.Locale;
 import java.util.Map;
-import org.jetbrains.annotations.NotNull;
-import org.jetbrains.annotations.Nullable;
+import org.jspecify.annotations.Nullable;
 
 abstract class ValueTypeImpl<T> implements ValueType<T> {
   private final Class<T> type;
 
-  ValueTypeImpl(final @NotNull Class<T> type) {
+  ValueTypeImpl(final Class<T> type) {
     this.type = type;
   }
 
   @Override
-  public @NotNull Class<T> type() {
+  public Class<T> type() {
     return this.type;
   }
 
@@ -51,13 +50,13 @@ private Types() {
 
     static ValueType<String> STRING = new ValueTypeImpl<String>(String.class) {
       @Override
-      public @NotNull String parse(final @NotNull String plainValue) throws IllegalArgumentException {
+      public String parse(final String plainValue) throws IllegalArgumentException {
         return plainValue;
       }
     };
     static ValueType<Boolean> BOOLEAN = new ValueTypeImpl<Boolean>(Boolean.class) {
       @Override
-      public @NotNull Boolean parse(final @NotNull String plainValue) throws IllegalArgumentException {
+      public Boolean parse(final String plainValue) throws IllegalArgumentException {
         if (plainValue.equalsIgnoreCase("true")) {
           return Boolean.TRUE;
         } else if (plainValue.equalsIgnoreCase("false")) {
@@ -69,7 +68,7 @@ private Types() {
     };
     static ValueType<Integer> INT = new ValueTypeImpl<Integer>(Integer.class) {
       @Override
-      public @NotNull Integer parse(final @NotNull String plainValue) throws IllegalArgumentException {
+      public Integer parse(final String plainValue) throws IllegalArgumentException {
         try {
           return Integer.decode(plainValue);
         } catch (final NumberFormatException ex) {
@@ -79,7 +78,7 @@ private Types() {
     };
     static ValueType<Double> DOUBLE = new ValueTypeImpl<Double>(Double.class) {
       @Override
-      public @NotNull Double parse(final @NotNull String plainValue) throws IllegalArgumentException {
+      public Double parse(final String plainValue) throws IllegalArgumentException {
         try {
           return Double.parseDouble(plainValue);
         } catch (final NumberFormatException ex) {
@@ -92,7 +91,7 @@ private Types() {
   static final class EnumType<E extends Enum<E>> extends ValueTypeImpl<E> {
     private final Map<String, E> values = new HashMap<>();
 
-    EnumType(final @NotNull Class<E> type) {
+    EnumType(final Class<E> type) {
       super(type);
       for (final E entry : type.getEnumConstants()) {
         this.values.put(entry.name().toLowerCase(Locale.ROOT), entry);
@@ -100,7 +99,7 @@ static final class EnumType<E extends Enum<E>> extends ValueTypeImpl<E> {
     }
 
     @Override
-    public @NotNull E parse(final @NotNull String plainValue) throws IllegalArgumentException {
+    public E parse(final String plainValue) throws IllegalArgumentException {
       final E result = this.values.get(plainValue.toLowerCase(Locale.ROOT));
       if (result == null) {
         throw doNotKnowHowToTurn(plainValue, this.type(), null);
diff --git a/src/main/java/net/kyori/option/value/package-info.java b/src/main/java/net/kyori/option/value/package-info.java
index c3d11d8..6069c57 100644
--- a/src/main/java/net/kyori/option/value/package-info.java
+++ b/src/main/java/net/kyori/option/value/package-info.java
@@ -3,4 +3,5 @@
  *
  * @since 1.1.0
  */
+@org.jspecify.annotations.NullMarked
 package net.kyori.option.value;
diff --git a/src/main/java9/module-info.java b/src/main/java9/module-info.java
index 73543f0..6d4da08 100644
--- a/src/main/java9/module-info.java
+++ b/src/main/java9/module-info.java
@@ -1,7 +1,9 @@
 /**
  * Feature flag system.
  */
+@org.jspecify.annotations.NullMarked
 module net.kyori.option {
+  requires static transitive org.jspecify;
   requires static transitive org.jetbrains.annotations;
 
   exports net.kyori.option;
diff --git a/src/test/java/net/kyori/option/OptionConfigTest.java b/src/test/java/net/kyori/option/OptionConfigTest.java
index 7ffec86..e6280a0 100644
--- a/src/test/java/net/kyori/option/OptionConfigTest.java
+++ b/src/test/java/net/kyori/option/OptionConfigTest.java
@@ -23,7 +23,6 @@
  */
 package net.kyori.option;
 
-import org.jetbrains.annotations.NotNull;
 import org.junit.jupiter.api.Test;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
@@ -173,7 +172,7 @@ void testVersionBetweenSteps() {
     assertEquals(true, versioned.value(TWO));
   }
 
-  private static @NotNull String key(final String path) {
+  private static String key(final String path) {
     return "option:test/" + path;
   }
 }