Suggestions for syntonly
The following packages have something in common with the package syntonly. The packages are ordered in decreasing similarity.
- xprintlen: Print TeX lengths in a variety of units
 - printlen: Print lengths using specified units
 - fix-cm: Permit Computer Modern fonts at arbitrary sizes
 - doc: Format LaTeX documentation
 - docstrip: Remove comments from file
 - inputtrc: Trace which file loads which
 - pdfsync: Provide links between source and PDF
 - cmdtrack: Check used commands
 - regcount: Display the allocation status of the TeX registers
 - showdim: Variants on printing dimensions
 - show2e: Variants of \show for LaTeX2ε
 - srcltx: Jump between DVI and TeX files
 - ted: A (primitive) token list editor
 - precattl: Prepare special catcodes from token list
 - mwe: Packages and image files for MWEs
 - prettytok: Pretty-print token lists
 - chkfloat: Warn whenever a float is placed “to far away”
 - magicnum: Access TeX systems’ “magic numbers”
 - pkgloader: Manage the options and loading order of other packages
 - testflow: A tool to validate PS/PDF output from LaTeX
 - qstest: Bundle for unit tests and pattern matching
 - regstats: Information about register use
 - cmextra-latex: Install macros for “standard” fonts not used by LaTeX itself
 - ifthen: Conditional commands in LaTeX documents
 - ltxdoc: Class for documented LaTeX macro files
 - structuredlog: Report files opened and closed in the log, including nesting level
 - unravel: Watching TeX digest tokens
 - plautopatch: Automated patches for pLaTeX/upLaTeX
 - listlbls: Creates a list of all labels used throughout a document
 - showhyphenation: Marking of hyphenation points
 - refcheck: Check references (in figures, table, equations, etc)