Is there an English word whose definition is the ability to tell truth from a lie?

Question

There doesn't seem to be an English word describing the ability to tell truth from a lie. I've Googled, and posted on my FB account, but can't seem to find a word that precisely describes this ability.

Discernment. M-W defines this as "able to see and understand people things, or situations clearly and intelligently." Best so far, but a bit off the mark. It does not precisely identify the ability to perceive and separate truth from falsehoods.
The antonym of gullible
A discerning ear
(Slang) anti-bs meter; able to discern bullsh!t.

Others have suggested guarded, prudent, realistic, astute, and perceptive... but none of these precisely describe the quality that I've described.
The word should fit 'XXXXXXX' in the following:

John is so gullible; he'll believe anything. Not so Jane, she is XXXXXXX. She has quite the discerning ear; you'll never be able to deceive her with a lie.

Here are some possibles (consulted thesaurus.com; listed antonyms for gullible; definitions from Google.)

discerning. Having or showing good judgment. Discussed above; best so far, but a bit off the mark.
astute. Having or showing an ability to accurately assess situations or people and turn this to one's advantage. Rejected because does not account for lies.
knowledgeable. intelligent and well informed. Does not speak to distinguishing truth from lies.
perceptive. Having or showing sensitive insight. Does not speak to discernment of truth or lies.
suspicious. Having or showing a cautious distrust of someone or something.. Speaks more to distrust than separation of truth from lies.
unbelieving. Not believing someone or something. Does not speak to the ability to distinguish truth from lies.

user242899 · Answer

How about the word wisdom?

Def: The ability to discern what is true, right, etc.
if you can discern truth then you automatically negate lies.

The use of the word discern in the definition also, in my opinion, doesn't pose a problem since it is defined as follows:
if you discern something, you are aware of it and know it. ie the truth

Collins dictionary.

Tom22 · Answer

I might suggest the word Sagacious

Sagacious combines some elements of "wise to the world" with the concept of a sharp and well considered use of intellect, as I understand the word

Sagacious at Dictionary.com adjective
  
  1.
  having or showing acute mental discernment and keen practical sense; shrewd:
  
  a sagacious lawyer.

Greybeard · Answer

There doesn't seem to be an English word describing the ability to tell truth from a lie.

That is because English is an excellent language that realises that the ability to tell truth from a lie 100% of the time does not exist.
As a consequence, any antonym for gullible, which does not mean "always accepts a lie as the truth" is not going to encompass this idea of infallibility.
The nearest you will get is a reasonable approximation:
OED
streetwise, adj.
Of a person: that has the skills and knowledge necessary for dealing with modern urban life; smart; tough. Of a thing: suitable for or reflective of modern urban life.
1949   P. W. Tappan Juvenile Delinquency xix. 538   She was streetwise enough not to get involved in the same area twice.
Canny
c. Cautious and careful in worldly or business matters; worldly-wise, shrewd.
1987   P. Wright & P. Greengrass Spycatcher vi. 73   In fact, the intelligence gathered was worthless. Khrushchev was far too canny a bird to discuss anything of value in a hotel room.
astute, adj.
Of keen penetration or discernment, esp. in regard to one's own interests; shrewd, subtle, sagacious; wily, cunning, crafty.
1878   R. B. Smith Carthage 331   He had, with the astute fickleness of a barbarian, come to a secret understanding with Scipio.
You will note that within the above definitions there are other close synonyms that you may find useful.

Is there an English word whose definition is the ability to tell truth from a lie?

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