Is there a language spec for clojure?

This is the closest thing to an official Clojure EBNF that you are likely to find.

https://github.com/laurentpetit/ccw/blob/3738a4fd768bcb0399630b7f6a6427a3066bdaa9/clojure-antlr-grammar/src/Clojure.g

There is no language specification. If there are any plans for one in the future, I haven't heard of them.

The grammar linked by fogus, which was within the Eclipse plugin Counterclockwise, is no longer used by that project and has been removed from it.

Clojure.g4, an ANTLR grammar

For a more up-to-date ANTLR grammar for Clojure, see Clojure.g4 (permalink) from grammars-v4, a collection of “grammars written for ANTLR v4”. Clojure.g4 is small and easy to read, and it has successfully parsed Compojure and clojure.core in the past, but that does not guarantee that it can parse all Clojure code correctly.

Clojure’s parser, LispReader.java

The most authorative specification of Clojure’s syntax is Clojure’s source code itself. Clojure does not use an abstract grammar, only a custom parser, but you can understand the grammar after careful study of the parser’s implementation. Here is Clojure’s parser: LispReader.java (permalink).

LispReader.java uses a few classes from other files in the same directory, such as LineNumberingPushbackReader, but most of the code is in that file. In LispReader, the main function is read. read uses isWhitespace to ignore whitespace and commas. It also detects numbers and hands off the parsing to readNumber. For most other symbols, such as ( and #, read hands off interpretation to the objects in the macros and dispatchMacros arrays. You can follow the code from there.

clojure.tools.reader, a parser written in Clojure

There is also a Clojure reimplementation of LispReader.java called clojure.tools.reader. Its source code might be easier to read than LispReader, since it is in Clojure, not Java. clojure.tools.reader has some differences from LispReader.java, which are mostly being able to read some minor extra syntaxes proposed for Clojure and handling errors better.