cobol-modernization

A guided process for converting COBOL programs, often used on mainframes, into Java. It includes build setup, removal of mainframe-specific dependencies, migration, and test validation.

In plain words
What is it for?
Use it to prepare a COBOL project, replace CICS or VSAM dependencies, translate the resulting COBOL into Java, and validate the migration with tests.
Why use it?
It breaks a large legacy-code migration into stages and keeps both COBOL and Java builds available while changes are checked.

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/openhands/extensions/cobol-modernization
Any agent
npx skills add OpenHands/extensions --skill cobol-modernization
Clone the repo
git clone --depth 1 https://github.com/OpenHands/extensions

Made for: Claude Code, Codex.

Per session 32 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 879 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 $0.00032 $0.00879
Opus 5 $0.00016 $0.00439
Sonnet 5 $0.00006 $0.00176
Haiku 4.5 $0.00003 $0.00088

Measured 2d ago against content hash 551452a76770, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

cobol-modernization 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 2d ago.

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.

plugins/cobol-modernization/skills/cobol-modernization/SKILL.md · 123 lines

How it starts

The opening of the file, as written. The whole thing — 123 lines — stays where its author put it; the contents beside it link to each section on GitHub.

End-to-end workflow for migrating COBOL codebases to Java.

Overview

This plugin orchestrates a multi-phase COBOL modernization project:

  1. Build Setup — Configure compilation for both COBOL and Java, create test fixtures
  2. Mainframe Planning — Document transformations needed to remove mainframe dependencies
  3. Mainframe Removal — Convert CICS/VSAM code to standard COBOL
  4. Java Migration — Translate standardized COBOL to idiomatic Java

Prerequisites

  • GnuCOBOL compiler (cobc)
  • Java 11+ with Maven or Gradle
  • Python 3.13 with uv
  • LLM API key (Anthropic or OpenAI)

Quick Start

export LLM_API_KEY="your-api-key"
export LLM_MODEL="anthropic/claude-3-5-sonnet-20241022"

uv run python -m lc_sdk_examples.cobol_modernization --src-path /path/to/cobol/project

PowerShell equivalent for the environment setup:

$env:LLM_API_KEY = "your-api-key"
$env:LLM_MODEL = "anthropic/claude-3-5-sonnet-20241022"

uv run python -m lc_sdk_examples.cobol_modernization --src-path C:\path\to\cobol\project

Workflow Phases

Phase 1: Build Setup

See ../build-setup/SKILL.md

Creates the foundation for the migration:

  • COBOL compilation environment (GnuCOBOL)
  • Java project structure (Maven/Gradle + JUnit 5)
  • Test fixtures with golden outputs from COBOL execution

Outputs:

  • build_notes.md — Build instructions
  • test-fixtures/ — Input/output test data
  • test_manifest.json — Test case mapping

Phase 2: Mainframe Planning

See ../mainframe-planning/SKILL.md

Creates a transformation guide without modifying code:

  • Maps CICS/VSAM constructs to standard COBOL equivalents
  • Documents error handling replacements
  • Identifies UI operations to stub

Output:

  • mainframe_dependency_removal_plan.md

Phase 3: Mainframe Removal

See ../mainframe-removal/SKILL.md

Applies the transformation guide:

  • Replaces EXEC CICS commands with file I/O
  • Adds FILE STATUS checking
  • Stubs BMS/screen operations

Read the full file on GitHub · 123 lines

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. 2d ago First seen · 123 lines · 32 tokens per session scan A 551452a76770

Subscribe to this mod's changes

cobol-modernization is a skill published in the GitHub repository OpenHands/extensions (137 stars, last pushed 4d ago), licensed MIT. It adds 32 tokens to every session and 879 once invoked, about $0.0002 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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