python-to-java

A guide for rewriting Python scripts as command-line programs in Java 25, using only Java's built-in libraries.

In plain words
What is it for?
Use it when moving Python scripts or a Python codebase to Java, including argument handling, files, processes, concurrency, and standard-library features.
Why use it?
It provides a way to decide whether each script should become one Java file or a small multi-file project, while accounting for shared code between scripts.

Skill for Claude CodeCodex

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/adambien/airails/python-to-java
Any agent
npx skills add AdamBien/airails --skill python-to-java
Clone the repo
git clone --depth 1 https://github.com/AdamBien/airails

Made for: Claude Code, Codex.

Per session 118 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 423 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00118 $0.00423
Opus 5 $0.00059 $0.00211
Sonnet 5 $0.00024 $0.00085
Haiku 4.5 $0.00012 $0.00042

Measured yesterday against content hash 7ec30f86be5c, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

python-to-java scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured yesterday.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

java/python-to-java/SKILL.md · 41 lines

What it actually says

Python to Java Migration

Convert Python scripts to idiomatic Java 25 CLI programs with zero external dependencies.

Decision: Single-File vs Multi-File

Evaluate before writing any code:

  1. Start with /java-cli-script — one Java file per Python script, no build tool
  2. Switch to /java-cli-app when any of these apply:
    • Multiple scripts share >100 lines of identical code (e.g. domain records)
    • A single script exceeds ~500 lines
    • Scripts import from each other in Python (from module import func)

When switching to /java-cli-app, extract shared code into common source files within the multi-file project.

Migration Process

  1. Read all Python scripts — understand dependencies between them (import graph)
  2. Identify shared codeutils.py, common helpers, shared data classes
  3. Decide single-file vs multi-file per the rules above
  4. Translate each script using the idiom mapping below
  5. Verify — run each script with -version to confirm compilation

Python to Java 25 Idiom Mapping

See references/idiom-mapping.md for the complete translation table covering argument parsing, file I/O, subprocess management, concurrency, and standard library equivalents.

Files

What ships with it

1 file beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. yesterday First seen · 41 lines · 118 tokens per session scan A 7ec30f86be5c

Subscribe to this mod's changes

python-to-java is a skill published in the GitHub repository AdamBien/airails (47 stars, last pushed 11d ago), licensed MIT. It adds 118 tokens to every session and 423 once invoked, about $0.0006 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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