I was wondering if there's an idiom or expression for a person who knows everything there is to know about his field of interest or expertise, practically no detail is unknown to them.

I thought of the expression: knowing like the back of hand, but I guess that has a geographical sense to it and is used for cities, streets and neighbourhoods. (Please correct me if I'm mistaken.)

I hope I was clear. Thanks in advance.


In this situation, I would say he "knows it backwards". The implication is that one knows something so thoroughly that they could do it in reverse.

Also consider

"knows it backwards and forwards"

{Cambridge Dictionary of American Idioms}

and "knows it inside out"

{McGraw-Hill Dictionary of American Idioms and Phrasal Verbs}.

"knows it like the back of his hand" does often, but not always, have a geographical connotation.

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  • This answers OP's next question, not this one. – Edwin Ashworth Oct 3 '15 at 13:46
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    It answers the question as it was originally written (at the time that I wrote this answer). This question has been edited since then. Did I deserve a downvote for the question being edited after I answered it? – Holly Oct 4 '15 at 2:12
  • ' ... an idiom for someone who knows' (the original) equally demands a noun or equivalent. – Edwin Ashworth Oct 4 '15 at 14:09
  • @EdwinAshworth The original question also said "My own guess would be something like this: Since he developed this software framework himself, he knows all the words and words of it." Not sure how that would be interpreted as a request for a noun specifically. – Holly Oct 4 '15 at 23:12
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    You're right; OP invites related forms as well as noun groups. The repeat question is thus a duplicate. // I've edited to add attributions; this gives me the chance to retract the downvote. – Edwin Ashworth Oct 5 '15 at 18:54

One idiom that people in the United States sometimes use to describe a person who possesses extensive, detailed knowledge of a particular subject is walking encyclopedia. Here is the entry for that term in Christine Amer, The American Heritage Dictionary of Idioms (1997):

walking encyclopedia A very knowledgeable person, as in Ask Ron—he's a walking encyclopedia of military history. A similar expression, a walking dictionary, was used by George Chapman in his poem "Tears of Peace" (c. 1600)

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That sounds like a "subject-matter expert (SME)."

A subject-matter expert (SME) or domain expert is a person who is an authority in a particular area or topic.

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    This answers OP's request inasmuch as it is a term for the person involved. But is it an idiom? – Edwin Ashworth Oct 4 '15 at 14:11
  • @EdwinAshworth: You're exactly right. I totally overlooked that an idiom was requested. I'm not sure if I should delete my answer or not. Do you think that is the proper protocol? – James Oct 5 '15 at 14:48
  • It's not an idiom, being totally transparent. But OP broadens with 'idiom or [other] expression' in the body of his post. Your answer looks OK to me; I'm really just asking about how common the expression is. Checking on the internet shows that it is far more common than I suspected. Don't delete; have an upvote instead. – Edwin Ashworth Oct 5 '15 at 19:10
  • I've since adjusted the title to correspond with OP's body question. – Edwin Ashworth Mar 30 '18 at 15:43

To know something like the back of one's hand.

To be intimately knowledgeable about something

This professor is extremely knowledgeable, he knew Physics like the back of his hand.

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Personally I think that has an intimate (or encyclopædic) knowledge of [field] is idiomatic per se.

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Consider every jot and tittle

Every minor detail. A jot is the horizontal mark on the letter "t", and a tittle is the dot above an "i" or a "j".

Urban Dictionary

Also from soup to nuts

Also, from A to Z or start to finish or stem to stern . From beginning to end, throughout, as in We went through the whole agenda, from soup to nuts, or She had to learn a whole new system from A to Z, or It rained from start to finish, or We did over the whole house from stem to stern. The first expression, with its analogy to the first and last courses of a meal, appeared in slightly different forms (such as from potage to cheese) from the 1500s on; the precise wording here dates only from the mid-1900s. The second expression alludes to the first and last letters of the Roman alphabet; see also alpha and omega. The third comes from racing and alludes to the entire course of the race; it dates from the mid-1800s. The last variant is nautical, alluding to the front or stem, and rear or stern, of a vessel.

As noted, also from A to Z, from start to finish and from stem to stern.

American Hertiage Dictionary of Idioms at thefreedictionary.com

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  • I like how jot and tittle sounds, but Google results are mostly about Bible. Is it a commonly used idiom? Considering the fact that no one else suggested this; is it an idiom the average English reader would understand? – Behdad Oct 2 '15 at 5:42
  • It is probably a bit archaic. I think most AmE speakers over 50 would know it, but younger, not so much. But that is just an impression. – bib Oct 2 '15 at 12:09
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    I know I messed up a little, but I think you should post your answer here. – Behdad Oct 3 '15 at 9:23

Given your example sentence, nuts and bolts is an idiom you could use.

Nuts and bolts: The basic practical details

Here are some examples of usage from Oxford Dictionaries Online:

The nuts and bolts of making a movie...

He tends to hire ambitious people who have their eye on a startup and a knack for the nuts and bolts of practice.

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  • As you mentioned in your post, nuts and bolts refers to the basic details of something. I was looking for an idiom describing every possible detail. However, if you still think your answer is valid, please post it here. – Behdad Oct 3 '15 at 9:27
  • @Behdad: In that case, I think I'll let it slide. Thanks for the comment. – Tragicomic Oct 3 '15 at 11:43

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