GraphQL queries are hierarchical so that the response mirrors the structure of the query. We found that there were needs of the query (query parameters and directives, for example) that didn't feel ideally represented in JSON, which is why we have a different syntax.

We've got a reference lexer and parser in JS at https://github.com/graphql/graphql-js/tree/master/src/langua..., and we have a parser in C++ with C and C++ APIs (that can be used to build a parser for other languages) at https://github.com/graphql/libgraphqlparser.