We Rewrote JSONata with AI in a Day, Saved $500K/Year | Reco

Reco's principal data engineer used AI to rewrite JSONata (a JavaScript-based JSON query language) as a pure-Go library called gnata in about 7 hours, spending $400 in AI tokens. The original setup ran jsonata-js pods on Kubernetes, costing ~$300K/year and adding ~150 microsecond RPC overhead per evaluation across billions of events. gnata uses a two-tier evaluation architecture: a fast path for simple expressions that operates directly on raw JSON bytes with zero heap allocations, and a full path with complete JSONata 2.x semantics. A streaming layer batches N expressions against each event, reading raw bytes only once. After a week of shadow-mode validation with 1,778 test cases and 2,107 integration tests, gnata replaced the RPC fleet entirely, delivering 25-1000x speedups. Combined with a rule engine refactor enabled by gnata's batch evaluation capabilities, the total savings reached $500K/year in under two weeks of work.