ZX Spectrum 48K

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BLUEEDITDEF FNREDCAPS LOCKFNMAGENTATRUE VIDEOLINEGREENINV. VIDEOOPEN #CYAN←CLOSE #YELLOW↓MOVEWHITE↑ERASE→POINTGRAPHICSCATBLACKDELETEFORMAT
SINASNCOSACSTANATNINTVERIFYRNDMERGESTR $[CHR $]CODEINPEEKOUTTAB©
READ~RESTORE|DATA\SGN{ABS}SQRCIRCLEVALVAL $LENSCREEN $USRATTR
LNBEEPEXPINKL PRINTPAPERL LISTFLASHBINBRIGHTIN KEY $OVERPIINVERSE

Load Spectrum media

TAP, TZX, SNA, Z80, RZX, or a ZIP containing exactly one supported Spectrum file.

No media loaded
Advanced toolsBASIC, recordings, stepping, rewind and debugger

Machine controls

Debug WorkbenchRegisters, source, disassembly, memory and reference

Registers

BASIC

Disassembly

    Memory

    Source

    1. Load a source or listing file to follow it beside the debugger.

    Assembler Reference

    Full sjasmplus documentation

    Free · Open source · Runs in your browser

    ZX Spectrum 48K Online Emulator

    Run a Sinclair ZX Spectrum 48K directly in your browser with this JavaScript web emulator. Load TAP and timed TZX tapes, ZIP files, SNA/Z80 snapshots and RZX recordings from your device or a URL, with fast tape loading, sound, Sinclair BASIC and built-in Z80 debugging tools.

    ZX Spectrum web emulator for games, BASIC and Z80 development

    This browser-based emulator recreates the original 48K Sinclair ZX Spectrum around a validated Z80 CPU core, 48K memory map, keyboard matrix, beeper, 50 Hz display and ULA timing behavior. It runs as a JavaScript application in a modern web browser, with no desktop emulator installation required.

    It is deliberately more than a quick game launcher. Media can come from your device or a web URL, and ZIP files can hold supported Spectrum media. The same page also combines Sinclair BASIC import/export, RZX playback, instruction stepping, reverse stepping, rewind history, live registers and flags, disassembly, memory inspection, raster timing and source-listing tools.

    TAP, TZX and URL loading

    Open .tap and .tzx tape images from your device, a ZIP file or a pasted URL. Tapes are inserted as complete cassettes and autoload from the first block, so the Spectrum and any custom loader decide when later blocks are read.

    SNA and Z80 snapshot support

    Load classic 48K .sna snapshots and compatible .z80 snapshots, including compressed or uncompressed version 1 files and extended snapshots containing the normal 48K pages. Save the current machine as an uncompressed 48K Z80 snapshot.

    Browser Z80 debugger

    Pause execution, step by frame or instruction, step backward, scrub rewind history, and inspect registers, flags, disassembly, memory, raster position and t-states. Load assembly/listing files beside the debugger and search the built-in sjasmplus reference.

    Supported ZX Spectrum file formats

    Format Browser support
    TAP Complete-tape loading through the emulated EAR input, starting from block 0.
    TZX Timed standard, turbo, pure-tone, pulse-sequence, pure-data, direct-recording and generalized-data blocks, plus pause and 48K tape-control blocks.
    SNA Load classic 48K SNA snapshots.
    Z80 Load compatible 48K Z80 snapshots and save the current state as an uncompressed version 1 Z80 snapshot.
    RZX Step through or play compatible 48K RZX input recordings with embedded or user-supplied SNA/Z80 snapshots.
    ZIP Open ZIP files containing supported Spectrum media, including files loaded from a web URL.
    BAS / TXT Paste or import Sinclair BASIC source, tokenize it into Spectrum memory, run it, and export editable BASIC text.

    Built-in ZX Spectrum and Z80 debugging tools

    The debugging workbench is aimed at people writing, studying or reverse-engineering Z80 and Spectrum software. It exposes live CPU state, flags, disassembly around the program counter, key memory regions, BASIC state, raster timing and an optional raster overlay. Resizable debugger panels can follow source listings while the emulator runs or steps, and the bounded reverse history allows frame rewind without taking a complete 48K memory copy at every checkpoint.

    Open-source JavaScript ZX Spectrum emulator

    The emulator code is open source under the MIT License. The bundled historical ZX Spectrum 48K ROM has its own terms, so the repository keeps the ROM and third-party notices separately.