What is the SP file format?
An .sp file is a plain-text SPICE netlist - a circuit description used by electronic simulation tools to analyze analog and mixed-signal circuits. SPICE (Simulation Program with Integrated Circuit Emphasis) was originally developed at UC Berkeley in 1973, and the .sp extension became a widely adopted convention in EDA (Electronic Design Automation) workflows, particularly in HSPICE and Spectre-based flows.
The file starts with a free-form title line, followed by element cards that describe components - resistors (R), capacitors (C), inductors (L), MOSFETs (M), BJTs (Q), voltage sources (V), current sources (I) - and their node connections. Dot-directives configure simulation types (.TRAN, .DC, .AC), define component models (.MODEL, .SUBCKT), and terminate the file with .END.
Because no single governing standard exists, SPICE dialects vary: Berkeley SPICE3, HSPICE, LTspice, PSpice, Spectre, and ngspice each differ in syntax, model parameters, and supported analyses. An .sp file written for one tool may need minor edits to work in another.
Typical use cases range from small student circuits (a few kilobytes) to large extracted transistor-level post-layout netlists reaching hundreds of megabytes. The .sp extension overlaps with the related .CIR format and .net, which share the same plain-text SPICE syntax.
Security & safety
RISK: LOWA SPICE netlist is plain text and harmless to open. The only caveat is that some simulators support .INCLUDE/.LIB directives and shell-out mechanisms; treat decks from untrusted sources with normal caution and inspect any referenced include files. SourcePawn .sp files are also plain text (source code).
Format details
in a nutshell- SourcePawn source code - Plain-text .sp scripting files for SourceMod plugins (Source-engine games like CS:GO); compiled to .smx.
- Shitennou game data - Data file associated with the Shitennou game, per legacy file databases.
- FORTH / generic source - Occasionally a generic source or text file in older toolchains.
Programs that open SP files
Windows3 apps
macOS1 app
Linux2 apps
Technical details
deep spec| Encoding | Plain ASCII / UTF-8 (practically 7-bit ASCII for all element cards and dot-directives) |
| Container | Plain text |
| Encryption | None (vendor model libraries may be encrypted separately, e.g., HSPICE .inc files) |
| Typical size | 1 KB - hundreds of MB (large extracted transistor-level netlists with parasitics can reach hundreds of MB) |
| Structure | Title line, then element cards (R/C/L/M/Q/V/I with node connections), dot-directives (.MODEL, .TRAN, .AC, .DC, .SUBCKT), and .END terminator |
| Element card notation | First character identifies component type: R=resistor, C=capacitor, M=MOSFET, Q=BJT, V=voltage source, I=current source |
| Dot-directives | .TRAN (transient), .DC (DC sweep), .AC (AC analysis), .MODEL (component model), .SUBCKT (subcircuit definition), .INCLUDE (external file) |
| Dialects | Berkeley SPICE2/SPICE3, HSPICE, PSpice, LTspice, Spectre, ngspice - syntax differs in parameters and supported analyses |
| Associated OS | Windows, Linux, macOS |
| Related extensions | .cir and .net share the same SPICE syntax; .lib and .mod store component model libraries |
| Historical origin | SPICE created at UC Berkeley in 1973; .sp extension convention popularized by HSPICE and Spectre commercial EDA flows |
| Released | 1973 (SPICE1, UC Berkeley); .sp convention popularized by HSPICE/Spectre flows |
| Latest version | No single spec; dialect-dependent (SPICE3f5 syntax is the common baseline) |
| Open standard | Yes · royalty-free |
| Specification | ngspice.sourceforge.io |
SP conversions
Community Q&A
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