nostics

Errors and warnings your users (and their agents) can actually act on.

Every diagnostic is a typed, structured object with a stable code, a clear explanation, a suggested fix, and a docs link. No more grepping log output or guessing what an error means.

[NUXT_B2011] Invalid plugin `/plugins/bad.ts`. src option is required.
├▶ fix: Pass a string path or an object with a `src` property to `addPlugin()`.
├▶ sources: /Users/me/projects/my-nuxt-app/nuxt.config.ts:14:3
╰▶ see: https://nuxt.com/e/b2011

Why

Library errors today are strings. Users scan them, agents pattern-match them, and everyone loses context. nostics turns each diagnostic into a Diagnostic instance: stable code, human why, actionable fix, structured sources, and a per-code docs URL. Humans get a searchable code and a fix in the same glance. Agents get machine-readable fields to dispatch on, instead of regexing message text.

Quick start

import { defineDiagnostics, reporterLog } from 'nostics'

const diagnostics = defineDiagnostics({
  docsBase: 'https://nuxt.com/e',
  reporters: [reporterLog],
  codes: {
    NUXT_B2011: {
      why: (p: { src: string }) => `Invalid plugin \`${p.src}\`. src option is required.`,
      fix: 'Pass a string path or an object with a `src` property to `addPlugin()`.',
    },
  },
})

// Report (continues execution) or throw — both are fully typed.
diagnostics.NUXT_B2011({ src: pluginPath })
throw diagnostics.NUXT_B2011({ src: pluginPath })

That's it. diagnostics.NUXT_B2011 is cmd+clickable, TypeScript checks params at the call site, and the result extends Error, so it works anywhere an Error does.

Dev reporter: pipe browser diagnostics to a file

Browser diagnostics are invisible to terminal-bound agents. The dev reporter fixes that: it forwards each diagnostic over Vite's HMR channel to a server-side plugin, which appends them to a log file your agent can tail. The Claude Code plugin sets this up automatically.

// src/diagnostics.ts
import { defineDiagnostics, reporterLog } from 'nostics'
import { devReporter } from 'nostics/reporters/dev'

export const diagnostics = defineDiagnostics({
  reporters: [reporterLog, devReporter],
  codes: {
    /* ... */
  },
})

import { nosticsServer } from 'nostics/unplugin'
// vite.config.ts
import { defineConfig } from 'vite'

export default defineConfig({
  plugins: [
    nosticsServer.vite({
      logFile: '.nostics.log', // default: .nostics.log
    }),
  ],
})

Now every diagnostic call in the browser is appended to .nostics.log as it happens. reporterLog still prints to the browser console. devReporter runs alongside it, not as a replacement.

Features

• Organized, stable codes. cmd+click to jump to your organized diagnostics definitions
• Structured Diagnostic instances. Extend Error, serialize via toJSON(), survive process boundaries
• Pluggable reporters. Console, file, HTTP, dev (Vite HMR), or your own
• Pluggable formatters. Plain text, ANSI colors, JSON
• Zero runtime dependencies

Claude Code plugin

Includes a Claude Code plugin so agents learn the API automatically: an auto-loaded reference skill and a /add-diagnostic command for scaffolding new codes.

gh api repos/vercel-labs/nostics/contents/install.sh --jq '.content' | base64 -d | bash

License

Apache 2.0