TPL/2

Compact Typed Path Line Protocol — browse and edit a tree of values on microcontrollers over serial.

The TPL Browser runs in your browser over HTTPS — no local install. Flash the demo sketch, plug in USB, and connect.

Open TPL Browser Read the spec Download Arduino demo
Browser and Arduino each hold the same path tree, connected by USB serial
The browser mirrors the device’s path tree over USB serial — browse branches, read and write leaves with plain text commands.

What is this?

TPL/2 is a lightweight, line-oriented text protocol for resource-constrained devices. The device exposes a hierarchical path tree — like a tiny read-only filesystem of typed settings and live readings. Clients discover structure with LIST, read leaves with GET or batch-read with MGET, and write stored values with SET.

Designed for Arduino-class boards: one request at a time, UTF-8 text, no JSON parser required on the firmware side.

GETRead one leaf (with optional ifvrev caching)
SETWrite a stored leaf (optimistic concurrency via vrev)
LISTList direct children of a branch (structure + optional values)
MGETRead multiple leaves by path in one round-trip

Demo device tree

The included Arduino sketch serves a small example tree:

/
├── server/
│   ├── proto     (s:, read-only)   → "TPL/2"
│   ├── name      (s:, rw)
│   ├── uptime    (u:, live)
│   ├── maxline   (u:)
│   └── trev      (u:, live)
├── cfg/
│   ├── mode      (u:, rw, 0–2)
│   └── name      (s:, rw)
└── io/
    └── ain0      (f:, live — simulated analog input)

On boot the device sends # TPL/2 ready before accepting commands.

Quick start

  1. Flash the demo sketch — download tpl_demo.ino, open it in the Arduino IDE (or arduino-cli), select your board, and upload. Default baud rate is 115200.
  2. Plug in USB — connect the board to your computer. Close the Arduino Serial Monitor if it is open (only one program can use the port).
  3. Open the TPL Browser — use the hosted app (tpl_browser.html on this site). Choose Simulated device to try without hardware, or USB Serial with your flashed board. Click Connect and browse the tree.
Simulated device works in any modern browser — no USB or HTTPS required. USB Serial needs Chrome or Edge on desktop and HTTPS (this site) or localhost. Serial data stays on your machine; nothing is sent to a cloud service.

Example session

C> LIST 1 /server values=1
S> OK 1 path=/server trev=1 count=5 next=-
S> ITEM 1 path=/server/uptime kind=L acc=r type=u val=u:42 live=1
S> END 1

C> MGET 2 /io/ain0 /server/uptime
S> OK 2 count=2 miss=0
S> ITEM 2 path=/io/ain0 val=f:23.50
S> ITEM 2 path=/server/uptime val=u:42
S> END 2

C> SET 3 /cfg/mode u:2 ifvrev=2
S> OK 3 path=/cfg/mode vrev=3

Download & distribute

End users only need the firmware. The TPL Browser is hosted on this website — no download or local web server required. To implement TPL/2 on your own hardware, start from the demo server and adapt the node table. A reusable Arduino library is under development — today the demo is a single self-contained sketch.

Download tpl_demo.ino Open TPL Browser

Files

  • tpl_demo.ino — flash this on your board Download
  • TPL Browser — hosted Web Serial client (tree, console, live poll) Open
  • tpl2_spec.md — protocol specification View
  • Arduino library — reusable TPL/2 server (under development) Coming

Developers can self-host the same static files (index.html, tpl_browser.html, spec, sketch). No build step.

Why TPL/2?