The Rakuten team had hundreds of files to modernize. Legacy patterns, dependency migrations - the kind of work that grinds engineers down for months.

They set up three things: a detailed spec, automated validation, and checkpoint commits. Then let Claude Code run.

Seven hours of autonomous operation. 99.9% accuracy. A project estimated at 3 months - done in weeks.

The engineers spent that time writing specs and reviewing output. Not typing.

Here's the full infrastructure setup that made it work →

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P.S. What's the most tedious codebase task on your plate right now - the one you keep putting off? Hit reply.