What is the TEC file format?
The .tec file format is used by TECkit, a text-encoding conversion toolkit developed by SIL International (Jonathan Kew). It contains a compiled version of a .map file - a human-readable mapping description also created with TECkit. TECkit's original purpose was converting 8-bit encoded text files into Unicode, but the software has since evolved into a more versatile encoding-conversion engine used by linguists and typographers worldwide.
Proper text conversion requires the corresponding .map source file. That file describes character-level mapping rules in plain text; running teckit_compile on it produces the binary .tec table, which the TECkit runtime engine (txtconv) then applies at conversion time. The .tec file is the deployment artifact - compact and optimized for fast lookup - while the .map file remains the human-editable source that documents the mapping intent.
.tec files are also used by XeTeX and related LaTeX-based tools for "on the fly" text conversion, typically when processing .tex documents that mix legacy 8-bit encodings with Unicode or that were originally composed in different writing systems or languages. TECkit is open source and available for Windows, Linux, and macOS via the silnrsi/teckit repository on GitHub.
Security & safety
RISK: LOWA .tec mapping table is inert data consumed by the TECkit engine; it carries no executable code and poses no direct risk. Only obtain TECkit from SIL's official site or GitHub repository, not from third-party "viewer" download portals.
Format details
in a nutshell- Tecplot ASCII data file - Plain-text numerical dataset (.dat/.tec) for Tecplot CFD/engineering visualization; the database's old name 'Tecplot ASCII data file' described this unrelated format.
Programs that open TEC files
Windows1 app
TECkit (teckit_compile / txtconv)
Open-source Use txtconv with the .tec to convert a text file; use teckit_compile to (re)build the .tec from its .map source. 
macOS1 app
TECkit
Open-source Build/install from the SIL repository, then convert text via the txtconv command line. 
Linux1 app
TECkit (textproc/teckit)
Open-source Install via package manager (e.g. FreeBSD textproc/teckit), then run txtconv -i in.txt -o out.txt -t mapping.tec. Technical details
deep spec| Format type | Compiled binary mapping table |
| Developer | SIL International (Jonathan Kew) |
| Source format | .map (human-readable TECkit mapping language source) |
| Compiler tool | teckit_compile - converts a .map source into a .tec binary |
| Runtime engine | txtconv - applies a .tec mapping table to convert input text |
| Primary use case | Character-level encoding conversion between 8-bit legacy encodings and Unicode |
| MIME type | application/octet-stream |
| Binary structure | Internal binary lookup table; not human-readable; treated as opaque binary by consuming tools |
| Magic bytes | No publicly documented magic-byte signature; identified by .tec extension and paired .map source |
| Platform support | Cross-platform: Windows, Linux, macOS |
| Source repository | silnrsi/teckit on GitHub (open source) |
| Engine integration | Used by XeTeX and LaTeX-based typesetting engines for inline encoding conversion |
| Encoding direction | Bidirectional - a single .map can define forward and reverse encoding mappings |
| Unicode normalization | Supports NFC/NFD normalization passes within the mapping rules |
| File pairing | Always paired with its .map source for human-readable documentation and future editing |
| Released | early 2000s; TECkit is open source (silnrsi/teckit on GitHub) |
| Open standard | Yes · royalty-free |
| Specification | software.sil.org |
TEC conversions
Community Q&A
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