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Type-Safe API Error Handling SDK for TypeScript
A TypeScript library that automatically formats API errors as structured JSON while propagating error response types from server to client. Initially targeting Elysia/Bun developers with Eden Treaty integration, then expanding to Hono and Fastify. Eliminates boilerplate, preserves end-to-end type safety, and supports RFC 7807 Problem Details.
Why this matters
You are a TypeScript developer building APIs with modern frameworks like Elysia or Hono. You want to return validation errors as structured JSON so your client app can parse them cleanly. But the framework only gives you plain text errors by default, so you write manual onError handlers with switch statements and custom error classes. Then you discover your type-safe client library no longer recognizes your custom error shapes, forcing you to add type assertions everywhere. You end up with brittle boilerplate on both server and client just to get a basic error response flowing with types intact. You wish there was a drop-in solution that handled this automatically.
- · Built for TypeScript full-stack developers building APIs with Elysia, Hono, or Fastify who need structured JSON error responses with end-to-end type safety on the client side.
- · Most likely monetization: freemium.
The Pain · Narrative
You are a TypeScript developer building APIs with modern frameworks like Elysia or Hono. You want to return validation errors as structured JSON so your client app can parse them cleanly. But the framework only gives you plain text errors by default, so you write manual onError handlers with switch statements and custom error classes. Then you discover your type-safe client library no longer recognizes your custom error shapes, forcing you to add type assertions everywhere. You end up with brittle boilerplate on both server and client just to get a basic error response flowing with types intact. You wish there was a drop-in solution that handled this automatically.
Score Breakdown
Market Signal
Go-to-Market
TypeScript full-stack developers using Elysia with Eden Treaty who have already written custom error handling workarounds and experienced the type safety gap
Approximately 5K-10K active Elysia developers currently, growing with Bun adoption; broader TypeScript backend market is ~200K
Hacker News launch targeting TypeScript developers, supported by dev Twitter and Elysia community engagement
$12/month for pro features (custom error schemas, multi-framework support, team error catalog) with a free open-source core
500 GitHub stars and 15 paying users within 30 days of launch, validated through a HN launch and Elysia Discord outreach
MVP Scope · 1–2 weeks
- Build core library: structured JSON error formatter that accepts validation errors and outputs RFC 7807 compliant responses
- Create Elysia plugin adapter that hooks into onError and automatically formats validation errors as JSON
- Implement type inference layer that declares error response shapes compatible with Eden Treaty client types
- Write integration tests with a sample Elysia app covering validation, not-found, and custom thrown errors
- Publish alpha package to npm and create a GitHub repo with documentation showing before/after comparison
- Build CLI tool that scans route definitions and generates client-side error type declarations
- Add support for custom error catalogs so teams can define domain-specific error codes with types
- Create Hono adapter to demonstrate cross-framework potential and broaden appeal
- Write a comparison blog post showing the boilerplate reduction versus manual workarounds
- Launch on Hacker News and share in Elysia Discord, tracking stars, npm downloads, and sign-ups
Differentiation
Why This Might Fail
Self-rebuttal — the most important trust signal
- 1Framework maintainers add native JSON error formatting with type safety in a future release, making the library redundant — this is the strongest risk since the issue already has a bounty and community attention within the framework itself.
- 2Developers in the TypeScript backend space have strong expectations for free open-source tooling, and the pain point may not be severe enough to justify a paid tier when a copy-paste workaround exists.
- 3The initial addressable market within Elysia is small enough that even with strong adoption, revenue may not reach a sustainable threshold before the broader TypeScript ecosystem evolves past the need.
Evidence Summary
How AI synthesized this insight — no verbatim quotes
Approximately six commenters expressed frustration with the lack of automatic JSON error formatting in a TypeScript backend framework, with multiple developers sharing detailed workarounds involving custom error classes, switch-case handlers, and client-side type assertions. Three commenters specifically noted that these workarounds break type safety in the framework's official client library, requiring manual type casts that undermine the value of a type-safe stack. A $100 bounty was offered for a resolution, indicating real but modest monetary willingness to pay. The pain extends beyond a single framework since type-safe error propagation is a universal gap in TypeScript backend development.
Action Plan
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Recommended Next Step
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Headline
Type-Safe API Error Handling SDK for TypeScript
Sub-headline
A TypeScript library that automatically formats API errors as structured JSON while propagating error response types from server to client. Initially targeting Elysia/Bun developers with Eden Treaty integration, then expanding to Hono and Fastify. Eliminates boilerplate, preserves end-to-end type safety, and supports RFC 7807 Problem Details.
Who It's For
For TypeScript full-stack developers building APIs with Elysia, Hono, or Fastify who need structured JSON error responses with end-to-end type safety on the client side
Feature List
✓ Automatic JSON error formatting for validation and runtime errors with zero config ✓ End-to-end type propagation so client SDKs know exact error response shapes ✓ RFC 7807 Problem Details compliance with customizable error envelope schemas ✓ Framework adapters for Elysia, Hono, and Fastify with shared core ✓ CLI tool to generate client-side error type definitions from route definitions ✓ Static analysis of route handlers to detect thrown error types and validation error shapes ✓ Automatic generation of TypeScript error type declaration files for client consumption ✓ Watch mode that regenerates types on save during development
Where to Validate
Share your landing page in r/GitHub · elysiajs/elysia — that's exactly where these pain points were discovered.
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