JWST user documentation will consist of articles, rather than monolithic handbooks.
Spectroscopy Made Easy (SME) is IDL software and a compiled external library that fits an observed high-resolution stellar spectrum with a synthetic spectrum to determine stellar parameters. The original paper describing SME is Valenti & Piskunov (1996).
Each release includes the SME User Handbook and an SME tutorial. Version 412 also includes a technical note that describes major changes to the way model atmosphere information is stored in SME structures. Each release includes the SME external library, compiled for Linux, OSX, and Windows systems.
Atomic and molecular line data formatted for SME may be obtained from VALD3, which supersedes the previous version of VALD. SME understands extended van der Waals encoding, which is enabled in the VALD3 unit selection configuration page. SME can solve for empirical log(gf) and damping parameters, using an observed spectrum of a star (usually the Sun) as a constraint.
Using empirical line data for wavelength ranges 5164-5190 (Mg b triplet) and 6000-6180 Å, Valenti & Fischer (2005) obtained spectroscopic parameters for 1040 cool stars. Damping wings of the Mg b lines are a useful gravity constraint for dwarfs cooler than about 6200 K. Mass, radius, gravity, and especially age in Table 9 were revised shortly after publication when a software bug was fixed.