Open SPEF files in your browser
The resistance and capacitance of a routed chip's wires, net by net. Open one right here, every net a row to sort and filter. Nothing leaves your device.
Or drop it anywhere on this page
What you'll see
Your parasitics open as a row for each net, the first rows on show while the rest are read.
- A row for each net • Capacitance, pins, driver and loads
- Sort and filter • Counts for every column
- Each net's network • Names from the name map
- Export • Save as CSV, Excel, JSON or Parquet
About SPEF
SPEF is the IEEE's format for a chip's parasitics. Once a design is routed, an extraction tool works out the resistance and capacitance of every wire and writes them as a SPEF, which timing tools read to know how slow each net really is.
A SPEF has a header with its units, a name map that turns long names into numbers like *42, the ports, and a block for each net with its total capacitance, the pins it joins and which one drives it, its capacitors to ground and to other nets, and the resistors between its points.
Filepeek reads the file in your browser in pieces and shows every net as a row: its total capacitance, pins, driver, loads, capacitors and resistors, to sort and filter like any table, each value exactly as the file writes it. A net's Network cell holds its block as written, with the name map's names put back, and Show details sums up the design, its units and its counts.
Standard Parasitic Exchange Format
.spef
Format
- MIME type
- text/x-spef
- Made by
- The IEEE, as part of IEEE 1481
- Released
- 1999
Inside the file
- Header
- The design, its units, the tool and the date
- Name map
- Numbers standing for long names
- Nets
- Each with its total capacitance and pins
- Parasitics
- Capacitors and resistors between points
Opens in every browser
Browsers download SPEF files, and timing tools need installing. Filepeek opens them in Chrome, Edge, Firefox and Safari, read in pieces so the first nets show at once.
- YouChromeOpens through Filepeek
- YouEdgeOpens through Filepeek
- YouFirefoxOpens through Filepeek
- YouSafariOpens through Filepeek
Questions
How do I open a SPEF file?
Drop it on this page or choose Peek a SPEF. Its nets show as rows while the rest of the file is read, with nothing to install.
Which nets have the most capacitance?
Click Capacitance to sort the nets by it, or filter it to a range. A column's card gives its lowest, highest and average, and every column sorts and filters the same way.
Can I see a net's resistors and capacitors?
Yes. Double-click its Network cell to see its block as the file writes it, its connections, capacitors and resistors, with the name map's names put back in place of their numbers.
Are the values rounded?
No. Each value shows exactly as the file writes it, in the units its header names, like pF for capacitance.
Can I save the nets as a spreadsheet?
Yes. Choose Export to save every net, or only the ones on show, as CSV, TSV, Excel, JSON, JSON Lines or Parquet.
Is my file uploaded?
No. The file is read inside your browser and never leaves your device.