How faithful it is

JNEXT is built from the official ZX Spectrum Next FPGA sources — the VHDL that describes the actual hardware. Where a machine's behaviour is ambiguous or undocumented, the answer is taken from that source rather than guessed at, and pinned there by a test. In practice this means the emulator's answer is the silicon's answer.

Two honest caveats:

• Extreme cycle-exactness is not a goal. "Good enough to develop games on" is. A handful of demos that depend on sub-scanline timing may not be pixel-perfect.
• JNEXT is beta. Rough edges exist and are listed rather than hidden — see chapter 8, Known issues, and the issue tracker below.