Automattic/harper · error · Error

Weirpack is missing manifest.json

Error message

Weirpack is missing manifest.json

What it means

packWeirpackFiles builds a Weirpack binary from a Map of filename→content and requires a manifest entry named manifest.json. Without it the archive has no manifest metadata, so packing is refused with 'Weirpack is missing manifest.json'.

Solutions

1. Add the manifest under the exact key 'manifest.json': files.set('manifest.json', JSON.stringify(manifest))
2. Normalize keys (strip leading './' or '/') when building the map from paths
3. Check your glob/gather step actually includes the manifest file
4. Verify the manifest JSON parses and has required Weirpack fields before packing

Example fix

// before
const files = new Map([['./manifest.json', manifestJson]]);
// after
const files = new Map([['manifest.json', manifestJson]]);

const manifestFilename = 'manifest.json';
if (!files.has(manifestFilename)) {
  throw new Error('Add manifest.json at the archive root before packing');
}

try {
  const bytes = packWeirpackFiles(files);
} catch (e) {
  if (e instanceof Error && e.message === 'Weirpack is missing manifest.json') {
    files.set('manifest.json', JSON.stringify(manifest));
    return packWeirpackFiles(files);
  }
  throw e;
}

When it happens

Trigger: Calling packWeirpackFiles (or the helpers built on it: packed, bytes, buildWeirpackBytes) with a Map that lacks the exact key 'manifest.json' — e.g. key 'manifest.MD', './manifest.json', or building the map conditionally.

Common situations: Path-prefix bugs when assembling the file map (join() prepending './'); loading files from disk where manifest.json wasn't included in the glob; renaming the manifest for organization.

Understand the failure class

Background: "File not found" and ENOENT errors: why libraries can't find a file that should exist — this error's family across 50 libraries.

AI-assisted analysis of Automattic/harper@5fe7d5ab76 (2026-09-06). Data as JSON: /api/errors/a52f73ee26389984. Report an issue: GitHub.

Appendix: source

Thrown at packages/harper.js/src/weirpack.ts:15

import { strFromU8, strToU8, unzipSync, zipSync } from 'fflate';

export type WeirpackArchive = {
	manifest: Record<string, unknown>;
	files: Map<string, string>;
};

const manifestFilename = 'manifest.json';

/** Convert a Weirpack file system into a real Weirpack binary by compressing and serializing them into a byte array.
 *
 * For clarity on what a Weirpack is, read [the Weir documentation.](https://writewithharper.com/docs/weir#Weirpacks) */
export function packWeirpackFiles(files: Map<string, string>): Uint8Array {
	if (!files.has(manifestFilename)) {
		throw new Error('Weirpack is missing manifest.json');
	}

	const entries: Record<string, Uint8Array> = {};
	for (const [name, content] of files.entries()) {
		entries[name] = strToU8(content);
	}

	return zipSync(entries, { level: 6 });
}

/** Decompress and deserialize a Weirpack from a byte array. */
export function unpackWeirpackBytes(bytes: Uint8Array): WeirpackArchive {
	const archive = unzipSync(bytes);
	const manifestBytes = archive[manifestFilename];
	if (!manifestBytes) {
		throw new Error('Weirpack is missing manifest.json');
	}

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