Notes from a 2 AM On-Call: Next.js Server Actions Silently Swallowing Zod Errors in Production

The Failure Symptom

[02:17:43] POST /api/actions/submit 200 OK 127ms [02:17:43] Client: formState.errors = {} [02:17:43] DB: 0 rows inserted [02:17:43] Sentry: 0 exceptions

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Our user-facing form returned success. The database wrote nothing. No errors surfaced client-side. SLA breach alerts fired 90 seconds later when the downstream ETL pipeline starved.

The actual payload that hit our Server Action:

{ "userId" : "usr_19xKlM" , "amount" : "not-a-number" , "currency" : null }

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Zod should have rejected this immediately. It didn't.

The Red Herring

Every Next.js 15 tutorial on Server Actions shows this pattern:

// actions/submit.ts ' use server '

import { z } from ' zod '

const schema = z . object ({ userId : z . string (), amount : z . number (). positive (), currency : z .…