---
package: superjson
version: "^2.2.1"
tier: core
decision: approved
date: 2026-05-14
deciders: [Danijel Martinek]
adr: null
lastRevalidated: null
is-sub-processor: false
processes-pii: false
filter-results:
  license: MIT
  types: native
  maintenance: active
  boundary-fit: pass
  shadow-check: pass
  eu-residency: n/a
  cve-scan: clean
  named-consumer: pass
verification-commands:
  - npm view superjson license
  - npm view superjson version
  - pnpm audit --audit-level=moderate
accepted-cves: []
---

## Filter: license

<!-- Result: MIT -->

`npm view superjson license` returns `MIT`. MIT is on the allowlist.

## Filter: types

<!-- Result: native -->

superjson is authored in TypeScript and ships its own `.d.ts` declaration files. No separate `@types/superjson` package is needed.

## Filter: maintenance

<!-- Result: active -->

Actively maintained. Last release < 18 months. Used widely in the tRPC and Next.js ecosystem.

## Filter: boundary-fit

<!-- Result: pass -->

superjson is the serialization transformer used by the tRPC layer (`@repo/core-shared`) to handle non-JSON-serializable types (Dates, Maps, Sets) over the wire. `core-testing` uses it for mock tRPC client setup. No boundary rules restrict superjson to a specific tier.

## Filter: shadow-check

<!-- Result: pass -->

superjson is the sole tRPC-compatible serialization transformer in the workspace. No competing serializer (devalue, msgpackr, etc.) is present.

## Filter: eu-residency

<!-- Result: n/a -->

superjson is a pure serialization library with no network communication, telemetry, or data transmission. EU residency does not apply.

## Filter: cve-scan

<!-- Result: clean -->

`pnpm audit --audit-level=moderate` reports no advisories against `superjson` at the time of this trace.

## Filter: named-consumer

<!-- Result: pass -->

`@repo/core-shared` uses superjson as the tRPC transformer. `@repo/core-testing` uses superjson for mock tRPC client configuration. Named, non-hypothetical consumers exist today.

## Prompt: replaces

superjson replaces the default JSON-only serialization in tRPC, which would fail silently when Date objects or other non-JSON types are passed through procedure calls.

## Prompt: migration-cost-out

Low. superjson is used as the `transformer` option in the tRPC router and client configuration — two call sites in `core-shared`. Replacing it requires swapping the transformer and ensuring the replacement handles the same non-JSON types. No feature package references superjson directly.

## Prompt: alternatives-considered

1. **devalue** — Supports more types but is less mature in the tRPC ecosystem; superjson is the de-facto tRPC transformer standard.
2. **JSON-only (no transformer)** — Rejected because it silently loses type fidelity for Dates and breaks any use case that returns or receives a `Date` value.
