Our Comprehensive Guide to RPG Modernization

Quick summary

RPG modernization helps enterprises update legacy RPG systems for modern platforms without disrupting critical operations. This guide explains what RPG modernization involves, why it matters, and how to approach it step by step. It also covers common challenges and best practices. Explore our blog for more insights on modernizing complex legacy systems.

Is your RPG codebase slowing down modernization efforts?

RPG code is still deeply embedded in many enterprise applications today. Since many of these systems were written years, or even decades, ago, working with them becomes harder over time.

Simple changes take longer, integrations become fragile, and improving performance requires more effort as complexity grows. RPG modernization helps address these challenges. Updating legacy RPG applications makes systems easier to scale, improves performance, and supports cleaner integration with modern platforms.

In this Kodesage guide, we’ll walk you through the RPG modernization process, its benefits, and the key steps for a successful migration.

Why listen to us

At Kodesage, we work directly with teams modernizing long-standing RPG systems. Our AI-driven platform supports code refactoring, migration planning, and system optimization. This guide reflects our experience helping teams automate complex analysis, reduce manual work, lower risk, and make clearer modernization decisions.

What is RPG modernization?

RPG modernization is the process of updating legacy RPG applications to work with modern technologies and platforms. It often includes: 

• Converting fixed-format RPG to free-form RPG to align code with modern RPG standards.
• Modernizing databases to support current schemas, access patterns, and technologies.
• Migrating RPG code to languages like Java to enable broader tooling and integration.

The process often happens in stages and may involve changes to code structure, data models, and deployment approaches. Regardless of scope, the goal is to place older RPG systems into environments that support modern tooling, architectures, and integration patterns.

Why modernize your RPG applications?

Legacy RPG systems often limit change, increase maintenance effort, and slow integration with newer platforms. Modernization ensures these systems stay reliable while supporting current business and technical needs.

Other common reasons to modernize legacy RPG systems include:

• Improved scalability: Modernized RPG systems handle higher workloads more effectively and support growth without increasing system complexity.
• Lower maintenance costs: Cleaner code and modern platforms reduce reliance on specialized skills and simplify long-term system upkeep.
• Better performance: Updated architectures and optimized code improve processing speed and system responsiveness.
• Easier system integration: Modernized RPG applications connect more easily with APIs, services, and external platforms.
• Stronger security and compliance: Modern environments support current security standards, access controls, and audit requirements.
• Better support for development teams: Clearer code structures and modern tooling make systems easier to understand, test, and change.

Next, let us see how teams can go about RPG applications modernization step by step. 

How to modernize RPG applications in 7 steps 

Step 1: Assess the current RPG environment 

RPG modernization starts with a clear view of the current environment. At this stage, teams review existing RPG code, databases, and integrations to understand how the system works today. This includes mapping data flows, identifying component dependencies, and locating where business rules live in the code.

Early findings often reveal problem areas, including those that are not included in the legacy documentation. These may include tightly coupled logic, outdated database structures, or undocumented links between programs and data. Identifying these issues upfront makes later modernization steps safer and more predictable.

At Kodesage, we support this step through a deep RPG specific concept miner. This ensures that we can extract key business concepts from complex RPG code and map dependencies across programs and databases.

After the system has been thoroughly mapped, it is time for knowledge extraction. In simple terms, this means generating comprehensive documentation that encapsulates every important details about the system.

Although every RPG project is unique in their own way, we recommend generating the following documents, in case they are not yet available or are outdated:

• Logical system design: in very simple terms, this document captures what the system actually does, including business rules, data flows and general system behavior
• Physical system design: simply put, this document covers how the system is implemented. It specifies the actual technology and infrastructure behind it
• API documentation: such documents describe how the system interacts with an API. It is an important puzzle piece, helping to capture how the system communicates with other systems
• RPG Module descriptions: detailed documentation of specific modules. These documents ensure that every module is captured in detail. Having every module well documented will also serve as a solid foundation for future migration planning
• RPG Workflow descriptions: going beyond modules, workflow documents capture specific workflows that are responsible for important business related tasks. Such documents can reveal important relationships across modules, or can even help with identifying inactive modules.

Kodesage is built for large legacy environments. Unlike regular documentation tools, we bring decades of legacy documentation experience via our rich template library. The Kodesage docs studio offers a wide range of pre configured but customizable templates, that cover most software documentation use cases. We rely on LLMs to write technical documents, which raises the question of consistency. Large Language Models are non deterministic, which means re-generating the same document can yield different results every time. We solve this problem by dividing each document template into sub sections, while sub sections are further divided into paragraphs. There are detailed prompts behind the scenes on a paragraph level that ensure high document quality.

Furthermore, Kodesage creates a dynamic knowledge base that is fed by multiple data sources, including:

• The entire codebase from source management systems
• Database schemas
• Issue ticketing systems including ticket history
• Internal knowledge bases
• Uploaded offline documents (e.g. administrator guides, or notes of senior architects)

This knowledge base captures every change in the connected data sources, which ensures that it is always up-to-date. Upon it's creation, the Kodesage engine performs intelligent chunking, language-agnostic parsing, and specialized embedding that improve the overall conceptual understanding for LLMs. This, coupled with the previously mentioned RPG specific concept miner ensures that there is no hallucination by models when writing documentation.

Step 2: Define a migration strategy

After assessing the current RPG environment, the next step is defining a clear migration strategy. This strategy sets direction and keeps modernization work focused.

A strong migration strategy outlines goals, timelines, and resource needs. Teams should decide what success looks like, which systems or modules to modernize first, and how progress will be measured.

However, not all RPG applications need the same approach. Some modules may require refactoring, others a full rewrite, and some can remain unchanged for now. The adopted migration strategy must factor this in to reduce risk and prevent issues. 

Timelines should also reflect system complexity and team capacity. Phased plans often work best, allowing teams to deliver value while limiting disruption.

Kodesage’s full system visibility can be a huge advantage here. Our platform ingests the entire codebase along with related sources such as ticketing systems, database schemas, wikis, and existing documentation.

This information is unified into a shared system view and visualized through a concept map. The map shows how modules, data, and business concepts connect across the environment. With this visibility, teams can decide what to modernize, when to do it, and how changes may affect the wider system.

Step 3: Choose the right tools and platforms

Choosing the right modernization tools and platforms shapes how smoothly RPG modernization moves forward. There is no single best option for every organization. The right choice depends on several factors, including:

• Technical constraints: Existing architectures, platform dependencies, and integration requirements shape which tools are viable.
• Team readiness: Available skills, experience with modern languages, and capacity for change influence tool selection.
• Long-term goals: Modernization tools should support where the system needs to be in the future, not just short-term fixes.
• Security requirements: Many enterprises require on-premise deployment and strict data controls to meet internal and regulatory standards.
• Level of system understanding: Limited documentation or loss of system experts increases the need for tools that expose business logic and dependencies.
• Future modernization needs: Tools should support ongoing change, not just a one-time migration.

Despite working with LLMs, Kodesage has been designed to deliver maximum data privacy. Our platform is on-premise first, which means it has been designed to work on on-premise servers. This means the platform has to work on smaller scale machines as well. This is achieved by working with open-weight LLM models that are strong enough to deliver solid performance, but small enough to work on medium range servers. Our research team is constantly testing and benchmarking LLMs, ensuring that Kodesage always comes with the optimum model. But in case a different model is preferred, it can easily be changed. But we are aware that not every team wants to to operate their own machines, therefore Virtual Private Cloud options on AWS, Azure and GCP are also an option.

Using open-weight LLMs ensures that costs do not have to be token based. The Kodesage pricing is tied to the number of distinct software systems, and not usage.

Overall, the high security - which enables even privacy sensitive organizations to connect entire codebases - along with the RPG specific concept mapping and configurability makes Kodesage a strong choice for complex projects.

Step 4: Plan and prepare data migration

Data migration planning starts well before any data is moved. Teams need a clear picture of how data is used, where it flows, and which RPG modules depend on it.

This step focuses on cleaning and validating data so it works correctly in the target system. Inconsistent formats, unused fields, and hidden dependencies can create problems later if they are not addressed early.

Planning should cover data ownership, validation rules, and migration order. Teams also need to decide which data moves first and which systems must stay in sync during the transition.

Kodesage simplifies this phase through system understanding rather than direct data movement. Our platform documents each key RPG module and component, along with its data dependencies and relationships.

Once this foundation is in place, we generate migration guides tailored to each module. These guides explain how data and logic should move, taking real dependencies and usage patterns into account.

Migration guides also provide step-by-step instructions for each module. They explain what to migrate, in which order, and what needs validation at each stage. When needed, guides can also include target-language examples. For example, teams can review Java equivalents of RPG modules to see how logic and data structures translate.

Clear preparation reduces migration risk. With accurate documentation and detailed guidance, teams can approach data migration with confidence and fewer surprises.

Step 5: Migrate the RPG code

Once the migration path is defined, teams can begin migrating RPG code to the target platform. This step focuses on moving business logic while preserving behavior and data integrity. 

Migration can take different forms: 

• Some teams convert RPG code to free-form RPG first. 
• Others move directly to a new language, such as Java, based on long-term goals and platform strategy.

Either way, code migration should follow the plan created earlier. Modules are migrated in sequence, with dependencies and integration points handled carefully. This reduces risk and avoids unexpected side effects.

Validation is also critical during this phase. Migrated code must be reviewed, tested, and compared against the original system to confirm functional consistency. This way, modernization can move forward without disrupting existing operations.

Kodesage supports this step through automated code conversion. Once the approach is defined, our platform converts RPG modules according to the migration plan. It applies system context during conversion, ensuring business rules, dependencies, and usage patterns are taken into account, rather than converting code in isolation. We also have an IDE integration, helping engineers to work directly in developer environments as they working on migrating various modules to the new programming language.

This approach reduces manual effort and limits errors. Teams can focus on review and validation instead of rewriting large portions of code by hand.

Step 6: Test the new system

Testing confirms the modernized system works as expected before it goes live. It also helps teams catch issues early, when fixes are easier and less disruptive.

Testing should cover core business workflows, edge cases, and integrations with surrounding systems. Performance testing is equally important, since modernized code must handle realistic transaction volumes and usage patterns.

A solid testing approach usually includes:

• Unit testing to validate individual components
• Integration testing to confirm systems work together correctly
• Regression testing to ensure new changes do not break existing behavior

Regression testing becomes especially important during phased migrations, where legacy and modernized components may run in parallel.

With Kodesage, teams can test with real system context. Our platform can simulate real-world scenarios based on actual workflows and dependencies. It can also generate tests automatically, including unit and regression tests. 

This reduces manual testing effort and helps QA teams focus on validation rather than test creation. Teams can also move forward knowing the new system meets functional and performance expectations.

Step 7: Post-migration support and optimization

RPG modernization does not end with testing. Post-migration support and optimization are equally important. Post-migration work focuses on keeping the system stable and easy to support over time. Once migration is complete, teams need strong visibility into both the old and new systems.

While Kodesage does not monitor errors or review code automatically, our platform supports teams after migration by:

• Helping production teams understand issues faster using shared system context
• Improving issue ticket analysis through documented business logic and dependencies
• Supporting QA teams with existing tests as the system continues to change
• Speeding up onboarding for new engineers through Ask Kodesage
• Keeping technical documentation current as systems evolve for long-term system health

Post-migration support is about maintaining clarity as systems evolve. With shared system knowledge, teams can respond faster, onboard more easily, and keep documentation current. 

This helps ensure RPG modernization continues to deliver value long after the migration work is complete. 

Common challenges in RPG modernization

Legacy modernization comes with challenges, and RPG modernization projects are not an exception. Knowing these issues early helps teams plan more effectively and reduce risk.

• Legacy code complexity: Older RPG systems often contain tightly coupled logic and limited documentation. Breaking code into smaller components and using automated analysis tools helps simplify migration planning.
• Data integrity issues: Inconsistent data formats and hidden dependencies can cause problems during migration. Cleaning and validating data before migration reduces errors and supports smoother transitions.
• Integration challenges: Legacy RPG systems may not integrate easily with modern platforms. Using APIs and modern integration layers helps connect systems without disrupting existing workflows.
• Skill gaps: Many teams depend on a small number of RPG experts. Upskilling existing staff, working with experienced partners, and automating analysis reduces reliance on specialized knowledge.
• Downtime and disruption: Large changes increase operational risk. Phased migrations and hybrid approaches allow systems to remain available while modernization progresses.
• Cost and resource allocation: Modernization can strain budgets if poorly planned. A phased roadmap helps spread cost and effort while keeping projects manageable.

Addressing these challenges early helps teams modernize RPG systems with greater control and fewer surprises.

Best practices for successful RPG modernization

RPG modernization works best when technical changes support clear business outcomes. Here are proven practices that help teams reduce risk and keep projects on track:

• Align modernization with business goals: Modernization should support real business needs, such as system reliability, integration, or long-term maintainability, rather than technical change alone.
• Use automated tools for code conversion: Automation reduces manual effort and lowers the chance of errors during code migration and refactoring.
• Choose scalable, future-ready platforms: Target platforms should support ongoing change, modern tooling, and integration with other systems.
• Migrate in phases to limit disruption: Phased migration allows teams to validate changes gradually while keeping systems available.
• Provide ongoing user training and support: Teams need time and guidance to work with modernized systems and new tools.
• Document the process for future reference: Clear documentation helps teams support, extend, and further modernize systems over time.

At Kodesage, our tools support these practices throughout the process. We assist with automation, testing, and documentation, helping teams move through RPG modernization with clearer insight and fewer manual steps.

Bring clarity to RPG modernization with Kodesage

Successful RPG modernization depends on clear planning, strong system understanding, and steady execution. Teams need visibility into both legacy and modern environments to move forward with confidence.

At Kodesage, we support RPG modernization through system understanding, automation, testing support, and always-current documentation. This helps teams reduce risk and maintain clarity throughout the journey.

Ready to modernize your RPG applications? Request a demo today and see how Kodesage can help simplify your RPG modernization journey.

Frequently asked questions (FAQs)

What is the difference between RPG and COBOL?

RPG and COBOL are both legacy programming languages used in enterprise systems. RPG is closely associated with IBM i environments and business applications, while COBOL is more common in mainframe systems. Their ecosystems, tooling, and modernization paths differ.

How do I choose the right RPG modernization tools?

Tool selection depends on system complexity, security requirements, team skills, and long-term goals. Teams should assess how well tools support code analysis, migration planning, testing, and documentation before committing.

How can I handle legacy data when modernizing RPG systems?

Start by understanding data usage and dependencies. Clean and validate data before migration, define clear ownership, and move data in phases to reduce risk during transition.

What are the costs associated with modernizing RPG applications?

Costs vary based on system size, complexity, and approach. Phased modernization helps spread effort over time and reduces risk compared to large, one-time migrations.

How can I measure the success of an RPG modernization project?

Success can be measured through system stability, performance improvements, reduced maintenance effort, and easier onboarding. Meeting planned timelines and avoiding disruption are also key indicators.

What happens to old RPG code after modernization?

Old RPG code is often retained for reference or phased out gradually. In many cases, it remains available until teams confirm the modernized system fully replaces its functionality.

How do I prioritize which RPG applications to modernize first?

Prioritization should consider business impact, risk, and maintenance effort. Applications that block change or require frequent updates are often strong candidates.