sveltejs/kit · error · Error

Cannot build with because Bun treats a route segment…

Error message

Cannot build with ${JSON.stringify(file)} because Bun treats a route segment starting with `:` as a parameter. Rename the file or route so no segment starts with `:`.

What it means

adapter-bun rejects route paths where any segment starts with ':' because Bun's router treats a leading colon as a dynamic parameter placeholder, which would collide with the literal colon in the emitted file path (and browsers request the colon raw, unencoded).

Solutions

Rename the segment to SvelteKit's dynamic route syntax: src/routes/[id]/ instead of src/routes/:id/.
Audit src/routes for any file or folder whose name starts with ':'.
Use a different adapter (e.g. adapter-node) if ':'-prefixed paths are genuinely required.

Example fix

// before
src/routes/:id/+page.svelte
// after
src/routes/[id]/+page.svelte

Defensive patterns

Strategy: validation

Validate before calling

import fs from 'node:fs';
import path from 'node:path';
const bad = [];
(function walk(dir) {
  for (const seg of fs.readdirSync(dir)) {
    const p = path.join(dir, seg);
    if (fs.statSync(p).isDirectory()) {
      if (seg.startsWith(':')) bad.push(p);
      walk(p);
    }
  }
})('src/routes');
if (bad.length) throw new Error(`Rename ':'-prefixed route segments: ${bad.join(', ')}`);

Type guard

const isBunSafeRoute = (file) => !file.split('/').some((s) => s.startsWith(':'));

Try / catch

try {
  await build();
} catch (e) {
  if (/segment starting with `:` as a parameter/.test(e.message)) {
    console.error('Convert :x route segments to [x] SvelteKit bracket syntax');
    process.exit(1);
  }
  throw e;
}

Prevention

Use [param] brackets, never ':param' folders, in src/routes
Grep the routes tree for ':'-prefixed names before building
Don't copy route folder names from Express/Next.js conventions

When it happens

Trigger: validate_file_paths splits the generated route file path on '/' and any segment begins with ':', e.g. a file/folder literally named ':id' under src/routes.

Common situations: A route directory or file accidentally named with a leading colon (e.g. src/routes/:id/+page.svelte) instead of SvelteKit's bracket syntax [id]; route folder names copied from another framework (Express/Next.js ':param' style).

Related errors

AI-assisted analysis of sveltejs/kit@03f1687fe6 (2026-09-02). Data as JSON: /api/errors/f34ba708036e9d7d. Report an issue: GitHub.

Appendix: source

Thrown at packages/adapter-bun/index.js:95

	if (precompress) {
		if (fs.existsSync(`${file}.br`)) meta.br = true;
		if (fs.existsSync(`${file}.gz`)) meta.gz = true;
	}

	return meta;
}

/** @param {string[]} files */
function validate_file_paths(files) {
	for (const file of files) {
		if (file.includes('*')) {
			throw new Error(
				`Cannot build with ${JSON.stringify(file)} because Bun treats literal \`*\` characters in route paths as wildcards. Rename the file or route to remove the \`*\` character.`
			);
		}
		// a leading ':' would need percent-encoding, but browsers request the colon raw
		if (file.split('/').some((segment) => segment.startsWith(':'))) {
			throw new Error(
				`Cannot build with ${JSON.stringify(file)} because Bun treats a route segment starting with \`:\` as a parameter. Rename the file or route so no segment starts with \`:\`.`
			);
		}
	}
}

/** @type {import('./index.js').default} */
export default function (opts = {}) {
	const {
		out = 'build',
		envPrefix = '',
		precompress = false,
		serverOptions = {},
		buildOptions = {}
	} = opts;

	return {
		name: '@sveltejs/adapter-bun',

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