How do I install the Jspecify Nullness skill?

Run npx skillmds@latest add alexandru/jspecify-nullness in your terminal (requires Node.js), paste this page's agent-chat prompt into Claude, Cursor, or any MCP-connected agent, or download the SKILL.md file and copy it into your agent's skills directory.

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Is Jspecify Nullness free to use?

Yes. Installing skills from SkillMD is free, and the skill stays under its author's original license.

Who published Jspecify Nullness?

alexandru (@alexandru) published this skill. Their other Agent Skills are listed on their SkillMD profile.

Jspecify Nullness by alexandru — Agent Skill

Name: Jspecify Nullness
Author: alexandru

Jspecify Nullness

JSpecify nullness annotations for Java APIs and tooling. Use when adopting or migrating JSpecify annotations, designing null-safe Java signatures, fixing generic bounds and type-use placement, or interpreting Kotlin interop, annotation-processor, and tool-conformance behavior.

alexandru f2bffbd 3 files · 16.0 KB Updated Sep 17, 2026

File contents

JSpecify Nullness (Java)

Quick start

Add org.jspecify:jspecify:1.0.0 as a visible API dependency for Java libraries.
Prefer @NullMarked at package or class scope; add @Nullable only where null is allowed.
Treat unannotated types outside @NullMarked as unspecified nullness, not non-null.
Decide generic bounds deliberately: <T extends @Nullable Object> accepts nullable type arguments; <T> does not in a null-marked scope.
Keep @Nullable/@NonNull in JSpecify-recognized type-use locations, especially for arrays, nested types, type arguments, and bounds.
Read references/jspecify-nullness.md before substantial annotation, migration, or tooling advice.

Workflow

Confirm consumer constraints: nullness checker, Kotlin compiler behavior, and annotation processors.
Add the JSpecify dependency without hiding it from downstream users.
Annotate nullable types first, then add @NullMarked at class or package scope.
Fix generics: choose nullable/non-null bounds and annotate type-variable uses only when the use differs from the type argument.
Compile examples for syntax, then run a JSpecify-aware nullness analyzer and fix findings before expanding scope.

Rules of thumb

Do not annotate local-variable root types or casts; annotate only nested type arguments/components there.
For fields, parameters, and returns, @Nullable String[] means nullable elements; String @Nullable [] means the array reference is nullable.
For nested types, annotate the nested type as Map.@Nullable Entry, not the outer type.
Use @NonNull T only to force a type-variable use non-null when the type argument may be nullable.
Use @NullUnmarked only as an incremental escape hatch inside a null-marked scope.

Output expectations

Provide annotated signatures and call-site implications.
Explain generic bound choices and type-use placement.
Call out tool-conformance limits instead of promising specific diagnostics.
For skill edits, run jbang skills/jspecify-nullness/scripts/verify-examples.java.

References

Load references/jspecify-nullness.md for source-backed guidance, examples, and representative prompts.

---name: jspecify-nullnessdescription: JSpecify nullness annotations for Java APIs and tooling. Use when adopting or migrating JSpecify annotations, designing null-safe Java signatures, fixing generic bounds and type-use placement, or interpreting Kotlin interop, annotation-processor, and tool-conformance behavior.---# JSpecify Nullness (Java)## Quick start- Add `org.jspecify:jspecify:1.0.0` as a visible API dependency for Java libraries.- Prefer `@NullMarked` at package or class scope; add `@Nullable` only where `null` is allowed.- Treat unannotated types outside `@NullMarked` as unspecified nullness, not non-null.- Decide generic bounds deliberately: `<T extends @Nullable Object>` accepts nullable type arguments; `<T>` does not in a null-marked scope.- Keep `@Nullable`/`@NonNull` in JSpecify-recognized type-use locations, especially for arrays, nested types, type arguments, and bounds.- Read `references/jspecify-nullness.md` before substantial annotation, migration, or tooling advice.## Workflow1. Confirm consumer constraints: nullness checker, Kotlin compiler behavior, and annotation processors.2. Add the JSpecify dependency without hiding it from downstream users.3. Annotate nullable types first, then add `@NullMarked` at class or package scope.4. Fix generics: choose nullable/non-null bounds and annotate type-variable uses only when the use differs from the type argument.5. Compile examples for syntax, then run a JSpecify-aware nullness analyzer and fix findings before expanding scope.## Rules of thumb- Do not annotate local-variable root types or casts; annotate only nested type arguments/components there.- For fields, parameters, and returns, `@Nullable String[]` means nullable elements; `String @Nullable []` means the array reference is nullable.- For nested types, annotate the nested type as `Map.@Nullable Entry`, not the outer type.- Use `@NonNull T` only to force a type-variable use non-null when the type argument may be nullable.- Use `@NullUnmarked` only as an incremental escape hatch inside a null-marked scope.## Output expectations- Provide annotated signatures and call-site implications.- Explain generic bound choices and type-use placement.- Call out tool-conformance limits instead of promising specific diagnostics.- For skill edits, run `jbang skills/jspecify-nullness/scripts/verify-examples.java`.## References- Load `references/jspecify-nullness.md` for source-backed guidance, examples, and representative prompts.

Frequently asked questions