Most solar inverter manufacturers give you an app. You can see your generation, your battery level, maybe a few charts. It's fine.
FoxESS did something different. They published an open API.
That might sound like a technical detail. It isn't. It's the difference between owning a car and owning a car with a bonnet you can actually open.
What an open API means in plain English
An API (Application Programming Interface) is a door into your inverter's data. Through it, software can read your system's live readings — solar generation, battery state of charge, grid draw, feed-in — and can push settings changes back to the inverter.
Most inverter manufacturers keep that door locked. The data exists, but only their own app can access it. You get what they give you, presented how they choose to present it.
FoxESS opened the door. They published the full documentation publicly at foxesscloud.com — what data is available, how to access it, how to control settings. Anyone can build with it.
That's a genuinely unusual thing for a Chinese hardware manufacturer to do, and the community has responded.
What the FoxESS app doesn't do
The FoxESS app (and the cloud portal) are decent for basic monitoring. But there are things they don't do:
They don't know your energy plan. The app has no idea whether you're on GloBird ZeroHero, Amber, or a flat-rate plan. It can't tell you whether your battery behaviour is winning you the $1/day VPP credit. It can't optimise your charging schedule for the free 11am–2pm window.
They don't act on forecasts. The app doesn't check tomorrow's weather and decide whether to force-charge tonight. It just runs the schedule you set and leaves it there.
They don't explain decisions. When your battery does something unexpected, the app shows you what happened but not why.
They don't compare costs. There's no "you drew 2.3kWh during peak hours today at 47.3¢ — that cost you $1.09" context. Just raw numbers.
None of this is a criticism of FoxESS — it's just that a hardware manufacturer's app is designed to show you your system is working, not to optimise your electricity bill.
What you can actually do with the API
The API gives you access to:
- Real-time data — PV generation per string, battery SoC, load power, grid draw/export, temperatures, all updated every few minutes
- Historical data — query any time range, all variables
- Reports — daily/monthly generation, feed-in, grid consumption, charge/discharge totals
- Settings control — set minimum SoC, enable/disable force charging, set charge windows, change work mode (Self-Use, Feed-in Priority, Backup, Force Charge/Discharge)
That last one — settings control — is what makes it genuinely powerful. You can write software that reads the weather forecast, checks your battery level, and adjusts your inverter's behaviour automatically. Every morning. Without touching a phone.
Getting your API key — 2 minutes
Your FoxESS API key is obtained from foxesscloud.com. Login, go to User Profile → API Management → Generate API key.
One important gotcha: the moment you generate the key it isn't obfuscated, so you need to copy it without changing screen or clicking any other button — the moment you leave the screen and come back it will be obfuscated. Do it on a desktop browser, not your phone.
Keep the key somewhere safe — a password manager is ideal. If you lose it or think it's been compromised, you can generate a new one and the old one immediately stops working.
The API has a rate limit of 1,440 calls per day per inverter — one per minute continuously — which is plenty for any monitoring or automation purpose.
What the community has built
This is where it gets interesting. Because FoxESS published their API, a community of developers has built tools on top of it — for free, openly, maintained by people who actually own FoxESS systems.
TonyM1958's FoxESS-Cloud Python library
The most comprehensive community tool. A Python library and set of Jupyter notebooks for accessing Fox cloud data via the REST API. Updated regularly — version 2.9.11 was released April 2026. If you're comfortable with Python this is the starting point for anything custom.
Energy Stats app
A third-party iOS/Android app built on the FoxESS API. More detailed than the official app, community maintained, free. Worth installing alongside the official app just to see what your data actually looks like.
Home Assistant FoxESS integration
Connects your FoxESS inverter to Home Assistant via the API. Enter your API key and inverter serial number — both available from the FoxESS Cloud portal. If you're running Home Assistant this opens up automations, dashboards, and integration with other home systems.
foxessprom — Prometheus exporter
For the technically adventurous — exports your inverter data as Prometheus metrics, which can feed into Grafana dashboards. Overkill for most people but produces beautiful real-time monitoring.
PVOutput integration
PVOutput is a free community site where solar owners log and share their system performance. Several tools exist to push your FoxESS data to PVOutput automatically, letting you compare your system's performance against others with similar setups and locations.
The AI angle — what's actually possible now
This is where it gets genuinely interesting for 2026.
Because the API supports both reading data and pushing settings, it's possible to build an AI layer that:
- Reads your live data every 5 minutes
- Checks tomorrow's weather forecast
- Knows your energy plan's rate structure and special windows
- Decides each morning whether to schedule force-charging
- Logs every decision in plain English so you know why it happened
- Lets you override anything with one button
We've built exactly this for a FoxESS KH9.9 system on Stradbroke Island — running on a small Docker stack, weather data from Open-Meteo, tariff logic from GloBird ZeroHero's rate structure. It's been running for several weeks and the ZeroHero $1/day credit has been won consistently.
It's not a product yet. But the pieces are all there, the API makes it possible, and the open source community tools mean you're not starting from scratch.
If this is something you'd want for your system — get in touch.
The broader point about open APIs
FoxESS isn't the only inverter brand with API access. SolarEdge has an API, Fronius has a local API, Sungrow has iSolarCloud with some API access. But the quality, documentation and community around FoxESS's API is notably good for a brand at their price point.
When you're choosing an inverter — or advising someone who is — the question "does it have an open API with a community behind it?" is worth asking. It's the difference between a device that does what the manufacturer decided it should do, and one that does what you need it to do.
For battery households trying to optimise around complex VPP tariffs, that difference is real money.
Interested in AI-assisted inverter optimisation for your system?
Get in touch