CheckThisFile Core
File integrity, inside your application.
Calculate fingerprints, compare files and check complete deliveries. A local library and command-line tool for developers and coding agents.
Install once. Run locally.
Node.js 22+, JavaScript and TypeScript. MIT licence. No dependencies, account, key, activation, telemetry or runtime network calls. Use it in your product without paying for operations.
npm install ./checkthisfile-core-0.1.2.tgz
./node_modules/.bin/checkthisfile compare approved.pdf received.pdf
./node_modules/.bin/checkthisfile manifest ./delivery > delivery.manifest.json
./node_modules/.bin/checkthisfile verify delivery.manifest.json ./received-deliveryDownload the versioned archive and checksum above. It includes the source and documentation. Installation can use the network; execution does not.
One check, a structured result
import { compareFiles, createFolderManifest, verifyFolderManifest }
from 'checkthisfile-core';
const result = await compareFiles('./approved.pdf', './received.pdf');
if (!result.matches) throw new Error('Different file bytes');
const manifest = await createFolderManifest('./delivery');
const check = await verifyFolderManifest(manifest, './received-delivery');
// check.matches, changed, missing, unexpectedSuitable for delivery checks, document intake, build artifacts and local agent workflows. Folder manifests use the same format as our web tool.
Try the folder toolAn open, documented format
SHA-256, relative paths and exact byte sizes. Strict validation, explicit resource bounds and JSON CLI results. Original files are never rewritten. The MIT licence keeps attribution in redistributed code; it does not require a logo in your documents.
Limits and reference trust
Version 0.1.2. Folder checks: 100 files, 50 MiB each and 250 MiB total. Manifests are unsigned and must come from a trusted source. A matching checksum checks bytes, not authorship or content safety. Concurrent hostile filesystem mutation requires OS isolation or immutable copies. Offline signed-receipt verification is a separate Python tool, not part of this Core release.
Need shared records and version status?
The hosted CheckThisFile service provides registration links, version history and scoped integrations. Choose it when your workflow needs those features. Core stays independent.
Explore the integrity API