Hono's onError hides exceptions from outer wrappers: keeping the stack trace

[virajrakholiya]

If you wrap app.fetch with a tracing or logging wrapper, one Hono detail matters: Hono catches every exception thrown in a handler and passes it to app.onError. The default handler logs it and returns a plain 500. So the outer wrapper never sees a thrown error, only a Response with status 500 and no stack.

To get the real exception, capture it where Hono hands it to you:

import { Hono } from "hono"
import { HTTPException } from "hono/http-exception"

const app = new Hono()

app.onError((err, c) => {
  if (err instanceof HTTPException) return err.getResponse() // expected 4xx, not a bug
  console.error(c.req.method, c.req.path, err.stack)
  return c.json({ error: "Internal error" }, 500)
})

Keep the HTTPException branch, or every throw new HTTPException(401) shows up as a crash in your error tracker.

I'm building Relia, an AI monitoring agent for small teams without an SRE. On Workers or Deno you wrap the app with export default { fetch: withRelia(app.fetch) }: each request becomes a span with path, status and duration, 5xx responses are flagged, and outgoing fetch and LLM calls are recorded. Because of the behaviour above, a 500 handled by onError arrives as a failed request without the original stack. On Node, the setup CLI detects Hono; requests are covered at the HTTP server level, with no Hono-specific spans. Relia suggests fixes but never touches code. Free plan and demo: https://app.tryrelia.com/demo?utm_source=github&utm_campaign=lead-agent

Where do you put error reporting in a Hono app: in onError, in a middleware, or outside app.fetch?