How we make this list: we compare pricing pages, product documentation and public user reviews. Ratings come from G2, Capterra or Trustpilot, with the date we checked them.
Key takeaways
- AWS Transform and Azure Migrate are the hyperscaler workhorses, largely free as tools because you pay for the destination cloud.
- CAST is the portfolio assessment standard: it images a whole estate before anyone commits to a migration path.
- vFunction owns Java and .NET monolith decomposition, producing the refactoring plan AI assistants then help execute.
- IBM watsonx Code Assistant for Z is the purpose built route for COBOL estates that are staying near the mainframe.
Quick comparison
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Starting priceFree for core migrations
Free planYes
AWS Transform is Amazon's agent powered workbench for getting estates onto AWS: VMware fleets, mainframe applications (mostly COBOL) and .NET Framework apps ported to modern .NET on Linux. It reached general availability in May 2025 and runs agent workflows behind human approval gates, which matters when an agent is rewriting code.
The pricing is unusual: as of the September 2026 pricing page, migration and modernization of Windows, VMware and mainframe systems is listed at no cost, while newer custom transformations meter at $0.035 per agent minute. Amazon can afford this because the real bill is the AWS estate you land on. Budget for the parallel run and the validation engineers, not the tool.
What we like- Agentic automation covers discovery, wave planning and code conversion for VMware, mainframe and .NET estates, core migrations carry no tool charge on the published pricing page, human approval gates keep engineers in control of generated changes, MGN replication is free for 90 days per server
Watch out for- Every road leads to AWS
- There is no multi cloud exit, custom and continuous modernization features are metered at $0.035 per agent minute, converted code still needs engineering validation before production, day two concerns like CI/CD and environments are out of scope
Starting priceFree for 180 days per server
Free planYes
Azure Migrate is Microsoft's front door for estates moving to Azure. It discovers what you run, maps dependencies, sizes the target, then moves servers with replication that is free for 180 days per machine before a modest per server charge applies. The GitHub Copilot modernization features layer AI assisted Java and .NET upgrades on top.
For estates already committed to Azure, this is the obvious first tool, and its assessment output is genuinely useful even before any move. The honest limit is scope: rehosting is the core strength. Replatforming and code level modernization lean on companion tools and your own team, and the total project cost still dwarfs the tool cost.
What we like- One hub for discovery, assessment and migration of servers, databases and web apps, free for the first 180 days per migrated server, then around $25 per month, agentless discovery keeps source systems untouched during assessment, App Service migration tooling suits .NET and Java web estates heading to Azure
Watch out for- Azure is the only destination, so the choice follows a cloud decision made earlier, assessment quality depends on observation period and CMDB hygiene, deeper modernization beyond rehosting needs the Copilot features and your own engineers
Starting priceSee website
Free planNo
CAST sells certainty before commitment. Its platform images an application portfolio at structural level: hidden dependencies, security flaws, cloud blockers, open source risk. Modernization programmes most often fail at the decision stage, by moving the wrong applications first, and CAST exists to make that decision on evidence.
It is an assessment tool, priced for enterprises with hundreds of applications, and it does not convert a line of code. Pair it with a conversion tool below, and treat its reports as the business case: which systems to rehost, which to refactor, which to leave on the mainframe and which to switch off entirely.
What we like- Scans 450 plus languages and frameworks for structural quality, security and cloud readiness, imaging shows cross tier dependencies that manual audits miss, portfolio view ranks which applications deserve investment and which should be retired, used by large enterprises and consultancies as the pre migration evidence base
Watch out for- Enterprise pricing by quote, aimed at portfolios rather than single applications, assessment is analysis only
- CAST tells you what to do, not does it, scan setup and interpretation need skilled hands
Starting priceSee website
Free planNo
Breaking a monolith is an architecture problem before it is a coding problem, and vFunction is built for that planning layer. It observes a running application, maps how classes and transactions actually connect, and proposes domain boundaries with the refactoring work itemised. Newer workflows hand that plan to AI code assistants for execution.
Buy it when the monolith is big enough that nobody fully knows its internal structure, which describes most decade old enterprise Java. Skip it for estates whose applications are small and understood; a whiteboard and two senior engineers beat a platform licence at that scale.
What we like- Combines static and runtime analysis to find real service boundaries inside Java and .NET monoliths, produces refactoring guidance that AI coding assistants can then execute against, measures architectural drift after the move, so the monolith does not quietly regrow, focused product rather than a cloud bundle
Watch out for- Decomposition planning only
- Execution still belongs to your engineers and other tools, quote only enterprise pricing, value depends on having monoliths complex enough to need analysis, which small estates do not
#5
IBM watsonx Code Assistant for Z
Best for: COBOL to Java translation
Visit ibm.com
Starting priceSee website
Free planNo
For mainframe estates, the honest options are convert, rehost on a mainframe runtime, or stay. IBM's assistant serves the first option and the stay-and-extend model: it translates COBOL to Java with awareness of the transaction and data layers the code depends on, and it lets you convert application by application rather than betting the estate on one cutover.
Pricing is by enterprise engagement; published figures for the base assistant start small, but real Z programmes are multi million efforts where tooling is a minor cost. IBM's advantage is accountability: one vendor owns the platform, the tool and the consulting bench. The risk is the mirror image: you are deepening an IBM relationship, so negotiate the long term shape before the first conversion.
What we like- Purpose built for COBOL to Java conversion on IBM Z, trained on COBOL and Java pairs, handles CICS, IMS and Db2 interop rather than pretending they do not exist, supports selective conversion, so parts of an estate can stay COBOL by design, backed by IBM consulting for programmes that need people as well as tooling
Watch out for- Enterprise engagement pricing, firmly inside the IBM ecosystem, converted Java still needs deep testing
- Translation is not verification, total programme costs for large estates run to millions regardless of tool
Starting priceFree
Free planYes
Konveyor is the open source member of this list, grown from the Migration Toolkit for Applications. It analyses codebases against migration rule sets, chiefly for moves onto Kubernetes, and reports what must change. Because it is open, your architects can read the rules, contest them and add your own.
It will not rewrite your application; it tells your engineers what rewriting is needed, which for many teams is the honest bottleneck anyway. Enterprises that want a throat to choke can buy supported distributions from vendors built on Konveyor, while the upstream project stays free for evaluation and internal use.
What we like- Open source under the CNCF umbrella, with no licence cost at any scale, analyses applications for migration to Kubernetes and flags the code changes required, rule based reports are inspectable and extendable by your own team, the commercial Tackle heritage means the rules carry real migration experience
Watch out for- Analysis and guidance rather than automated conversion, community support model
- Enterprise support comes via vendor distributions, Kubernetes is the assumed target, narrower than the hyperscaler toolkits
Starting priceSee website
Free planYes
Moderne handles the mechanical 80 percent of code modernization: version upgrades, API migrations, framework changes, security fixes, applied as reviewed pull requests across a whole estate at once. Its transformations are deterministic recipes rather than generated guesses, so the diffs are auditable and repeatable, which regulated industries care about.
Pair it with an assessment tool to decide what to change, and with engineers for the 20 percent of code where the recipe cannot decide. For a Java estate facing repeated framework upgrades across hundreds of services, it is often the highest return tool on this list.
What we like- Built on OpenRewrite, the deterministic recipe based refactoring engine, runs the same transformation across hundreds of repositories with auditable diffs, framework upgrades (Spring Boot, Jakarta, Java versions) are the home ground, free for open source projects
Watch out for- Deterministic recipes cover mechanical change
- Ambiguous code still needs humans or LLM tooling, enterprise pricing by quote for private estates, JVM ecosystem is the centre of gravity, other languages are thinner
#8
GitHub Copilot App Modernization
Best for: In IDE Java and .NET upgrades
Visit github.com
Starting priceIncluded with Copilot plans
Free planNo
Microsoft folded modernization into GitHub Copilot as agent driven upgrade workflows: point it at a Java or .NET project, pick the target version, and it works through the upgrade, explaining changes as it goes. For teams already on Copilot, the marginal cost of trying it is near zero, which makes it the easiest pilot on this list.
Its boundary is ambition. It modernizes projects, not portfolios, and offers no view across an estate. Use it as the execution hand for upgrades your assessment already justified, and keep humans reviewing every generated change, especially around security configuration and dependency swaps.
What we like- Works inside the IDE where engineers already are, so adoption friction is lowest here, covers Java and .NET version and framework upgrades to Azure targets, bundled into Copilot Business and Enterprise plans many teams already pay for, produces changes as ordinary code the team reviews in pull requests
Watch out for- Upgrade scope rather than estate transformation
- No portfolio planning, Azure flavour to the guidance even when the code could run elsewhere, Copilot plan required, so it is not a standalone purchase, agent output varies and needs the same review as any generated code
How we chose
We picked tools across the four real jobs: hyperscaler migration (AWS Transform, Azure Migrate), portfolio assessment (CAST), architecture and decomposition (vFunction), code conversion and refactoring (IBM, Moderne, GitHub Copilot) and open source analysis (Konveyor). Pricing is taken from published vendor pages where they exist (AWS, Azure, Konveyor) and marked See website where vendors sell by enterprise quote. AWS marketing claims about developer years saved were not repeated as facts. We did not claim hands-on testing.
Assess before you convert. The common failure pattern is buying a conversion tool first, then discovering the estate contains applications nobody owns, systems that should be retired, and dependencies that cross every boundary. A portfolio pass with CAST, Konveyor or a hyperscaler discovery tool pays for itself by shrinking the programme: most estates find 10 to 20 percent of applications can be switched off outright.
Then order the work by risk and value. Rehost the stable and understood systems first, while licences are still funded. Refactor the applications whose change rate justifies it. Convert mainframe code only where the skills cliff or the business case is real, because conversion is the most expensive and riskiest route of the three. Retire aggressively throughout; every retired system is budget returned.
Finally, price the whole programme, not the tool. Include the parallel run period, data migration testing, licence true ups, retraining and the validation engineers who will review machine converted code line by line in the critical paths. Vendors quote the conversion; the business pays for everything around it. Programmes that budget honestly for that surrounding work are the ones still running in year two.
Frequently asked questions
Should we rewrite, rehost or convert our legacy application?
Rehost when the application works and the goal is leaving a data centre. Convert when the platform itself is the problem, such as COBOL skills retiring. Rewrite rarely, and only small, high value pieces: full rewrites carry the worst failure record in this industry. An assessment tool can put numbers on each option per application.
How much do these tools cost compared with the whole project?
Tools run from free (Konveyor, the hyperscaler migration cores) to enterprise contracts for CAST, vFunction and IBM. In every case the tool is a small share of programme cost; infrastructure, licences, parallel running and validation engineering dominate. Budget the programme, then fit the tool inside it.
Can AI convert COBOL to Java safely on its own?
Tools from IBM and AWS automate translation and produce working code, but every credible vendor and consultancy pairs conversion with structured testing, because translated code that compiles can still behave differently under load or edge cases. Treat conversion as a strong first draft with a testing programme attached.
What is the difference between CAST and vFunction?
CAST assesses a whole portfolio: structure, quality, security and cloud readiness across hundreds of applications and languages. vFunction goes deep on one kind of problem, decomposing a Java or .NET monolith into services. Many programmes use CAST to decide, then vFunction to plan the hard refactors.
Is open source Konveyor enough for an enterprise migration?
For analysis and planning, often yes, especially for Kubernetes targets. What it does not give you is a support contract or automated conversion. Large enterprises commonly run the commercial distributions built on Konveyor, or pair it with hyperscaler migration tools for execution.
Sources we checked (0)
Is your product missing or out of date?
We review this list regularly. Vendors can request a listing, send updated pricing or ask about featured placement.
Shihab Mia · Founder, Rankite
Shihab has 5+ years in B2B and SaaS SEO. He writes Rankite's software buying guides from pricing pages, documentation and public user reviews. More about Shihab.
AWS Transform
Azure Migrate
CAST Software
vFunction
Konveyor
Moderne