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All StringsTheory apps work offline and require no account to use core features. If you need help, we're here.

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For questions, bug reports, feature requests, or license help — reach out anytime.

Our Apps

macOS + iPad + iPhone

StringsTheory INV

Inventory, work order, and production management for repair shops, luthiers, and small manufacturers. Track inventory, manage repairs from intake to invoice, run COGS reports, design and print labels, and sync with Square, Shopify, and Google Sheets. Available as a subscription — the Monthly plan includes a 14-day free trial. Help & Glossary →

macOS + iPad + iPhone

StringsTheory Tech Tools

Twenty-two precision tools for tube amp builders, technicians, and guitar techs — bias and component calculators (Ohm's Law, resistance, capacitance, filters, LED, clipping, speakers, attenuator), reference databases (607+ tubes, a 754-amp database, ~9,000 semiconductors, rectifiers, pickups, reverb tanks, dating codes), plus a chromatic tuner, live spectrum analyzer, and string tension calculator. Works entirely offline — no account required. One-time purchase. Help & Glossary →

macOS + iPad

StringsTheory Design

Tube amplifier circuit analysis toolkit with eight integrated tools: Tonestack Calculator (Bode plots for 52 tone circuits), PSU Designer (time-domain simulation with 173 rectifier models), Load Lines (Koren-model operating-point analysis with a distortion analyzer), Bias (three methods with a live dissipation gauge), Tube Data (3,727 tubes with pinouts and a substitution checker), Semiconductors (~9,000 transistors, diodes, and ICs), Circuit Calcs (17 bench calculators), and Build Planner (transformer matching with 479 amp references). Fully localized in 6 languages. Works entirely offline — no account required. One-time purchase. Help & Glossary →

Hardware appliance · Coming soon

StringsTheory Print Server

Dedicated network appliance that turns any USB thermal printer (Dymo, Brother, Zebra, Rollo) into a wireless, AirPrint-discoverable label printer. Smart routing by name, role, or label size; 80+ built-in label stocks; touchscreen management; over-the-air updates. Designed for 24/7 unattended use. One-time purchase. Help & Glossary →

macOS · Offline fork of INV

StringsTheory Privacy Edition

Offline-only fork of StringsTheory INV for high-security and data-sovereign environments. Zero network calls after activation. No cloud sync, no integrations, no telemetry — just the full inventory, work order, and production toolkit running entirely on your local machine. One-time purchase ($399.99), license key activation. Learn more →

Frequently Asked Questions

Do your apps require an internet connection?

No. All StringsTheory apps work fully offline. Some optionally check for announcements, but this never requires internet and fails silently. StringsTheory INV can optionally sync with Square, Shopify, and Google Sheets when online.

What platforms do your apps run on?

StringsTheory INV runs on Mac, iPad, and iPhone. Tech Tools runs on Mac, iPad, and iPhone. Design runs on Mac and iPad. The Print Server is a dedicated hardware appliance that works with any device on your network.

Do you collect any personal data?

No. None of our apps include tracking, analytics, or advertising. Tech Tools and Design collect zero data. INV collects account info only if you subscribe to cloud sync. See our privacy policy for details.

Is my data stored in the cloud?

By default, no — all data stays on your device. StringsTheory INV offers optional cloud sync on the Annual plan, but it's off by default and must be explicitly enabled.

What's the difference between INV Monthly and Annual?

Both include all core features. Annual adds unlimited work order emails, custom email sender domain, cloud sync across Mac, iPad, and iPhone, multi-user access with roles, and the web app companion. See the full comparison.

Can I sync INV between Mac, iPad, and iPhone?

Yes, with the Annual plan. Cloud sync is bi-directional across all your devices with conflict resolution, selective sync by data type, and a full sync log. It's optional — the app works fully offline on each device.

Can I export my data from INV?

Yes. CSV export is available for inventory, customers, production, and work orders. You can also create full backups and restore them at any time. Your data is always yours.

What printers does INV work with?

INV has a built-in label designer that prints to any system printer. For network label printing, the StringsTheory Print Server supports Dymo, Brother, Zebra, Rollo, and any CUPS-compatible printer.

What tube types does the bias calculator support?

60+ tube types including EL34, 6L6GC, KT88, EL84, 6V6, 300B, KT66, 6550, 7591, and many more. You can also create custom tube definitions with any max dissipation rating.

Is the tube data in Design accurate?

Tube specifications are sourced from manufacturer datasheets (RCA, Mullard, Philips, GE, Tung-Sol). Rectifier max filter capacitor values have been individually verified against original PDF datasheets. Always cross-reference critical safety values against the original datasheet for your specific tube.

What file formats does Design support?

Tonestack configurations save and load as JSON. PSU designs use the PSUD2-compatible .psu binary format.

What printers does the Print Server support?

Dymo (LabelWriter 300 through 5XL, Twin Turbo, DUO), Brother (QL-700, QL-800, QL-1100), Zebra (ZD420, GK420, ZP450), Rollo, and any CUPS-compatible printer via USB.

Do I need to install drivers on my phone or computer to use the Print Server?

No. The Print Server handles all drivers internally. Your iPhone, iPad, Mac, Android, and Windows devices connect automatically via AirPrint, Mopria, or network sharing — no software to install.

How do I report a bug or request a feature?

Email info@stringstheoryinv.com — we read every message.

Good to know

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