If you run M-x json-pretty-print on this buffer contents:

{"t": 259}

You get an error
Bad JSON object key: t

It seems like the json parser is converting the string "t" into the
symbol t which is being treated specially?





In GNU Emacs 26.3 (build 1, x86_64-apple-darwin18.2.0, NS appkit-1671.20
Version 10.14.3 (Build 18D109))
 of 2019-09-02 built on builder10-14.porkrind.org
Windowing system distributor 'Apple', version 10.3.2022
Recent messages:
Loading vc-svn...done
Loading autorevert...done
For information about GNU Emacs and the GNU system, type C-h C-a.
Quit
ls does not support --dired; see ‘dired-use-ls-dired’ for more details.
Quit
command-execute: The mark is not set now, so there is no region
Mark set
json-encode-key: Bad JSON object key: t

Configured using:
 'configure --with-ns '--enable-locallisppath=/Library/Application
 Support/Emacs/${version}/site-lisp:/Library/Application
 Support/Emacs/site-lisp' --with-modules'

Configured features:
NOTIFY ACL GNUTLS LIBXML2 ZLIB TOOLKIT_SCROLL_BARS NS MODULES THREADS

Important settings:
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: JavaScript

Minor modes in effect:
  override-global-mode: t
  global-auto-revert-mode: t
  display-time-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  column-number-mode: t
  line-number-mode: t
  transient-mark-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr warnings emacsbug message rmc puny rfc822 mml
mml-sec epa derived epg gnus-util rmail rmail-loaddefs mm-decode
mm-bodies mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader
sendmail rfc2047 rfc2045 ietf-drums mm-util mail-prsvr mail-utils js
advice sgml-mode dom json map imenu thingatpt dired dired-loaddefs
elec-pair cl-extra help-mode use-package use-package-ensure
use-package-delight use-package-diminish use-package-bind-key bind-key
easy-mmode use-package-core finder-inf info package epg-config
url-handlers url-parse auth-source cl-seq eieio eieio-core cl-macs
eieio-loaddefs password-cache url-vars seq byte-opt gv bytecomp
byte-compile cconv edmacro kmacro format-spec server autorevert
filenotify cus-start cus-load vc-svn bdc-indent cc-mode cc-fonts
easymenu cc-guess cc-menus cc-cmds cc-styles cc-align cc-engine cc-vars
cc-defs cl-loaddefs cl-lib time time-date tooltip eldoc electric
uniquify ediff-hook vc-hooks lisp-float-type mwheel term/ns-win ns-win
ucs-normalize mule-util term/common-win tool-bar dnd fontset image
regexp-opt fringe tabulated-list replace newcomment text-mode elisp-mode
lisp-mode prog-mode register page menu-bar rfn-eshadow isearch timer
select scroll-bar mouse jit-lock font-lock syntax facemenu font-core
term/tty-colors frame cl-generic cham georgian utf-8-lang misc-lang
vietnamese tibetan thai tai-viet lao korean japanese eucjp-ms cp51932
hebrew greek romanian slovak czech european ethiopic indian cyrillic
chinese composite charscript charprop case-table epa-hook jka-cmpr-hook
help simple abbrev obarray minibuffer cl-preloaded nadvice loaddefs
button faces cus-face macroexp files text-properties overlay sha1 md5
base64 format env code-pages mule custom widget hashtable-print-readable
backquote threads kqueue cocoa ns multi-tty make-network-process emacs)

Memory information:
((conses 16 459220 15608)
 (symbols 48 31276 1)
 (miscs 40 62 287)
 (strings 32 108877 1948)
 (string-bytes 1 2792952)
 (vectors 16 49371)
 (vector-slots 8 918195 17836)
 (floats 8 64 200)
 (intervals 56 375 1)
 (buffers 992 14))