A mainframe hall: rows of tape and disk cabinets, operators working at a shared console.

Modernise mission-critical software, safely.

Streamline the modernisation process. Enhance control, visibility and verification. Reduce risk and cost in complex migrations.

Get a demo See how it works
8x

faster legacy migration or more

4x faster than standard agentic coding tools.

10+

languages: 4GL family, C, C++, C#/.NET, COBOL, Go, Java, JavaScript, TypeScript, Perl, PHP, Python, Rust

If it builds on Linux, we can port it.

93%

of tests still pass after rewriting 21 codebases in another language. Best published result: 48%.

Half of the differences our proofs caught would have slipped past the tests.

Measured on RepoMod-Bench, a public benchmark of 21 codebases. See the results

Streamlining modernisation in practice

A network rack: patch panels and managed switches, with ranks of teal ethernet cables looped between them.
Technical case
Perl to Rust migration

Modernisation becomes safer and faster when every slice has an explicit scope, rollbacks and evidence.
An Amsterdam canal at sunset, tour boats moored along the quay in front of the Munttoren.
Customer case
Frontend modernisation

Tackling a frontend migration 15 years past due in bite-size pieces.
Someone in a suit reading the business pages of a newspaper, market tables in view.
Customer case
Legacy PHP upgrades

Maintenance can continue without making senior engineers responsible for every repetitive detail again.
Explore the features of the platform
// legacy modernisation

Migrations are risky and costly.

Every company must keep systems secure, current, and compliant. Software platforms are aging out, and extended security contracts further pile on to maintenance costs. High risk projects require strict and slow management.

Bosun mitigates risk and increases velocity.

Streamline the modernisation process
Every production behavior is inventoried up front and ordered by dependency. Missing building blocks become their own slices, before the first behavior that needs them.
Enhance control, visibility and verification
One test across two implementations. Equal results are the default, and only explicitly declared differences are allowed.
Reduce risk and cost in complex migrations
A router chooses per action which way it goes. Every migrated behavior rolls back on its own, and what has not been migrated keeps running untouched on the existing system.

Modernising critical software infrastructure.

Bosun analyses your codebase, assesses your migration path and architectural options. Your engineers approve the migration path and work items. The Bosun process is structured, repeatable and AI-supported, with accurate, comprehensible and traceable evidence, on-premise and with sovereign AI models.

  1. Assess Find the seam
  2. Strategize Choose both architectures
  3. Map patterns Make translation consistent
  4. Bootstrap Prepare coexistence and rollback
  5. Choose slices Pick the next small behavior
  6. Migrate one slice Prove, route, and observe
Learn more about modernisation with Bosun
// from the blog
All posts
11 NOV 2026

93% on RepoMod-Bench: porting 200K-line codebases with a proof in the loop

Bosun's Parity workflow on all 21 cases of RepoMod-Bench, three runs each. Taking the best run per case, 93% of hidden tests passed, against 74% for the paper's Codex setup on the same model and 48% for the best published agent; a 211K-line C++ port passes every hidden test. Half of the differences the proofs found are behaviour the tests never check. Method, limits and the full dataset.

Read the post
6 NOV 2026

Swiftide 0.33 and 0.34 - Agent contrib tools, typed task graphs, rustdoc tools, and more

Swiftide 0.33 and 0.34 ship file and planning tools for agents, typed task graphs with fan-out and joins, tool schemas read from rustdoc, streaming command output, and new docs at swiftide.rs.

Read the post

Get Bosun updates.
No noise.

New features, migration guides, and practical content on keeping your codebase healthy.

✓ Check your inbox to confirm your subscription.
! Oops! Something went wrong, please try again.
We respect your privacy. Unsubscribe any time.
Start with a proof of value.

One modernisation solution with demonstrable value. Bosun engineers work with your engineers to connect Bosun safely to your environment and set up the migration process.

Get a demo Take the legacy survey
You bring access to the codebase, impactful cases and reviewers. Bosun brings installation, workflow, guidance and measurement.
Supported by