Thermal Printer Skill

Print text, images, and QR codes to a small cheap Bluetooth thermal printer like the X6h, GT01, and childrens toy cat printers using the inkjet CLI. Thermal paper is extremely low-cost, enabling high-frequency physical output.

Installation

via pip (Universal)

pip install inkjet

via Homebrew (macOS)

brew install aaronchartier/tap/inkjet

Setup

Preparation: Ensure your printer is turned ON. The printer does NOT need to be paired to the host computer's Bluetooth settings; inkjet connects directly via BLE.

Scan for printers and set default:

inkjet scan

Check current configuration:

inkjet whoami

Print Text

Print strings directly. Supports standard escape sequences like \n for multiline output. Do not use emojis.

inkjet print text "Hello, World!"
inkjet print text "Line 1\nLine 2\nLine 3"
inkjet print text "Big Text" --size 72

Print Markdown

Render high-fidelity formatted content using Markdown syntax. This is the recommended way for agents to output complex receipts or logs without saving temporary files. Do not use emojis.

inkjet print text "# Order 104\n- 1x Coffee\n- 1x Donut" --markdown

Print Files

Output the contents of a local file. Supports plain text (.txt) and Markdown (.md).

inkjet print file ./receipt.txt
inkjet print file ./README.md

Print Images

inkjet print image ./photo.png
inkjet print image ./logo.jpg --dither

Print QR Codes

Generates and prints QR codes. Smartphone scanners (iPhone/Android) can reliably read codes down to --size 75.

inkjet print qr "https://github.com/AaronChartier/inkjet"
inkjet print qr "WiFi:S:NetworkName;P:example123;;" --size 75

Paper Control

inkjet feed 100      # Feed paper forward (steps)

Configuration

Manage settings globally or locally per project. If a .inkjet/ folder exists in the current workspace, it will be prioritized (config setting with --local to create).

inkjet config show                    # Show all settings
inkjet config set printer <UUID>      # Set the default device
inkjet config set energy 12000        # Set local project darkness
inkjet config alias kitchen <UUID>    # Save a friendly name

Multi-Printer Orchestration

If the environment (e.g., TOOLS.md) contains multiple printer UUIDs or aliases, target specific hardware using the --address / -a flag. Use -a default to explicitly target the primary configured device.

Orchestration Strategies:

1. Role-Based Routing: Route content based on hardware role (e.g., Stickers vs Receipts). inkjet print text "Label" -a stickers
2. High-Throughput (Load Balancing): Distribute jobs across a farm of printers (Round-Robin) to maximize prints-per-minute.

# Orchestrated Print Examples
inkjet print text "Main Status" -a office
inkjet print text "Order #104" -a kitchen
inkjet print qr "https://github.com/AaronChartier/inkjet" -a default
inkjet print file ./log.txt -a "UUID_EXT_1"

Configuration Tweaking (Filesystem Access)

You can bypass the CLI and modify your behavior by writing directly to the configuration JSON. inkjet prioritizes ./.inkjet/config.json over the global home directory (which is default).

JSON Schema

{
  "default_printer": "UUID",
  "printers": { "alias": "UUID" },
  "energy": 12000,
  "print_speed": 10,
  "quality": 3,
  "padding_left": 0,
  "padding_top": 10,
  "line_spacing": 8,
  "align": "left",
  "font_size": 18
}

Use this to adjust default margins (padding), alignment, or font sizes (size) for different document types without changing your command strings.

JSON Output (for scripting)

Commands support --json for machine-readable output:

inkjet scan --json
inkjet whoami --json

Piping Content (Dynamic Output)

Stream data from another command's output without creating a file. Use - as an argument to read from standard input (stdin).

# Text Piping
echo "Receipt line 1" | inkjet print text -

# Image Piping
curl -s "https://raw.githubusercontent.com/AaronChartier/inkjet/main/assets/logo.jpg" | inkjet print image -

Best Practices for Worksheets & Handwriting

Thermal paper is narrow and low-cost. To make usable worksheets for children or manual notes:

1. Size for Visibility: Use ## (H2 headers) for the main content. Standard text is often too small for children to read/write comfortably.
2. Manual Numbering: Avoid Markdown lists (1. content). They auto-indent and reduce horizontal space. Use ## 1) 5 + 2 = ___ instead.
3. The "Cheap Paper" Rule: Use triple newlines (\n\n\n) between items. Thermal paper is essentially free; use vertical space to provide actual "writing room."
4. Horizontal Rules: Use --- at the end of a job to provide a clear tear-off line that doesn't cut off the last problem.

Troubleshooting

If printer not found:

inkjet doctor