A COBOL guide for mainframe and legacy business systems. COBOL is a long-established language still used for large-scale banking, insurance, and other business processing.

Use it when editing .cob files, working with mainframe transaction systems, handling decimal financial data, or moving COBOL applications to Linux or cloud environments.

It helps maintain or migrate older systems while preserving their precise business rules and fixed-point arithmetic, which is useful for currency.

cobol — Skill for Claude Code and Codex by G1Joshi

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.

Any agent

npx skills add G1Joshi/Agent-Skills --skill cobol

Clone the repo

git clone --depth 1 https://github.com/G1Joshi/Agent-Skills

Made for: Claude Code, Codex.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

README.md

[![agentmods](https://agentmods.dev/badge/skills/g1joshi/agent-skills/cobol/github.svg)](https://agentmods.dev/skills/g1joshi/agent-skills/cobol)

Your own site

<a href="https://agentmods.dev/skills/g1joshi/agent-skills/cobol"><img src="https://agentmods.dev/badge/skills/g1joshi/agent-skills/cobol/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

Your own site · 80×15

<a href="https://agentmods.dev/skills/g1joshi/agent-skills/cobol"><img src="https://agentmods.dev/badge/skills/g1joshi/agent-skills/cobol.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 22 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 308 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.

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.

Model	Per session	Once invoked
Fable 5.1	$0.00022	$0.00308
Opus 5	$0.00011	$0.00154
Sonnet 5	$0.00004	$0.00062
Haiku 4.5	$0.00002	$0.00031

Measured 9d ago against content hash 9bf56aa4e5e7, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-12, from the pricing page.

Security

Grade A, and why

cobol 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 9d 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.

skills/languages/cobol/SKILL.md · 45 lines

What it actually says

COBOL

COBOL runs 70% of the world's business transactions. Modern COBOL (GnuCOBOL 3.2 / IBM Enterprise COBOL) supports JSON, XML, and Object-Oriented features.

When to Use

Mainframes: The backbone of banking/insurance systems (CICS/IMS).
Legacy Migration: Moving logic to Linux/Cloud using GnuCOBOL.
Decimal Arithmetic: Native fixed-point math (PICTURE 9V99) is unmatched for currency.

Core Concepts

Divisions

IDENTIFICATION, ENVIRONMENT, DATA, PROCEDURE.

Picture Clause

01 SALARY PIC 9(5)V99. Defines data layout precisely.

PERFORM

The main control flow loop.

Best Practices (2025)

Do:

Use GnuCOBOL: For local development on Mac/Linux.
Use VS Code: With the bitlang.cobol extension.
Unit Test: Use COBOL Check or ZUnit.

Don't:

Don't use GO TO: Use PERFORM and structured programming.

References

GnuCOBOL FAQ

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.

9d ago First seen · 45 lines · 22 tokens per session scan A 9bf56aa4e5e7

Subscribe to this mod's changes

cobol is a skill published in the GitHub repository G1Joshi/Agent-Skills (12 stars, last pushed 7mo ago), licensed MIT. It adds 22 tokens to every session and 308 once invoked, about $0.0001 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 2026-09-03.

Backend and APIs agent-skills antigravity chatgpt claude cursor gemini

api-and-interface-design

Guides stable API and interface design. Use when designing APIs, module boundaries, or any public interface. Use when creating REST or GraphQL endpoints, defining type contracts between modules, or establishing boundaries between frontend and backend.

addyosmani/agent-skills · 49 tokens

cobol