Open VCD files in your browser
The waveform every Verilog and VHDL simulator can dump, from Icarus Verilog to Questa. Open one right here, every signal on one time ruler, with no GTKWave. Nothing leaves your device.
Or drop it anywhere on this page
What you'll see
Your waveform opens with its signals down one side, grouped by scope, and their values along one time ruler.
- Every signal by its scope • Buses in hex, decimal or binary
- Two cursors that snap to edges • The time between them and its frequency
- Find a signal by its name, or a value with =
- Export • PNG, and the values between the cursors as CSV
About VCD
Value Change Dump came with Verilog, and IEEE 1364 set it down in 1995 so any simulator's waveforms could be read by any viewer. Icarus Verilog, Verilator, Questa, VCS, Xcelium, Vivado's simulator and GHDL all write it, and cocotb's tests leave one behind.
A VCD is text: a header of scopes, the modules and blocks of the design, each declaring its wires, regs, integers and reals with a short code, then a time stamp for each moment something changed, followed by the codes that changed and their new values. A bit is 0, 1, x or z, a bus a string of them, and a real a number.
Filepeek reads it in your browser, the changes in slices so a large dump opens, and draws every signal on one time ruler: bits as lines high and low, x in coral and z in amber, buses as their values in hex, decimal or binary, and reals as curves. Fold a scope, drag or pinch to move and zoom, click to put cursor A and shift-click for B, with the time between them and its frequency, find a signal by its name or a value with =, and save the view as PNG or the values between the cursors as CSV.
Value Change Dump
.vcd
Format
- MIME type
- text/x-vcd
- Made by
- IEEE, in the Verilog standard (IEEE 1364)
- Released
- 1995
Inside the file
- Scopes
- Modules, blocks and functions of the design
- Variables
- Wires, regs, integers, reals and strings
- Changes
- A time, then each new value
- Values
- 0, 1, x and z, bit by bit
Opens in every browser
Filepeek opens VCD files in Chrome, Edge, Firefox and Safari, read in slices so large dumps open. On their own, browsers show them as text or download them.
- YouChromeOpens through Filepeek
- YouEdgeOpens through Filepeek
- YouFirefoxOpens through Filepeek
- YouSafariOpens through Filepeek
Apps that open VCD
- WindowsGTKWave or Surfer, free
- MacGTKWave or Surfer, free
- iPhone and iPadNo app opens it
- AndroidNo app opens it
Questions
How do I open a VCD file without GTKWave?
Drop it on this page or choose Peek a VCD. Every signal opens on one time ruler in your browser, grouped by its scope, on a phone too.
How do I measure the time between two edges?
Click near the first edge to put cursor A, then shift-click near the second, or choose Measure and click, for cursor B. Each snaps to the nearest change, and the strip shows the time between them and its frequency.
Can I see a bus in decimal?
Yes. Choose Hex, Dec or Bin in the strip, and every bus shows its values that way, on its lane, by its name and in the CSV.
Can I find when a signal takes a value?
Yes. Pick the signal, then type = and the value in Search, like =ff or =1010, and the arrows step cursor A to each time it takes it, in hex, decimal or binary. A name finds the signal.
Can I save part of a waveform?
Yes. Put the two cursors around it and choose Export, then Save the values, for a CSV of every change between them, or Save the view for a PNG.