Semmle 1.18
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About the QL language

QL is a declarative, object-oriented query language, optimized to analyze hierarchical data structures, in particular, databases representing source code. Since QL treats code as data, you can use simple QL queries to explore your code quickly and accurately. The basic syntax for a QL query will look familiar to anyone who has used SQL, but is used somewhat differently. 

 Click to show 'Hello world' and the basic syntax...

A QL query is defined by a select clause, which specifies what the result of the query should be. The following is an example of a complete query:
select "Hello, world!"

Its result is just the string "Hello, world!".

More complicated queries typically follow the following structure:

from /* ... variable declarations ... */
where /* ... conditions ... */
select /*... expressions ... */

For example, the following query computes the number 42:

from int x, int y
where x = 6 and y = 7
select x * y

QL code can contain C-style comments. An end-of-line comment is introduced by "//", and a (possibly multiline) delimited comment is introduced by "/*" and terminated by "*/".


The rules and metrics used by Semmle analysis are written using QL. This ensures that they can be extended or revised easily to keep up with changes in definitions of best coding practice. Every Semmle release includes improvements to existing rules as we work towards the ultimate goal of 100% precision. For details of the standard rules implemented by QL queries supplied by Semmle, see Semmle standard rules.

You can also write your own queries to identify code that breaks your team's guidelines for best practice or customize the default rules to accommodate a new framework.

Learning QL

If you are new to QL and want to start learning the language, see Learning QL

This page gives an overview of available learning resources. These include introductory tutorials, practical suggestions for writing queries, and comprehensive reference topics.

QL tools

There are a number of tools you can use to write and run QL queries locally and see the results of analyses:

Technical background

For more background information about the QL language and how Semmle's analysis works, see the following topics:

For any questions or feedback relating to documentation, please contact For any other support issues, please contact your organization's email address. Using your organization's support address ensures that your message will be received as soon as possible by a member of our support team, even when the staff that you normally speak to are out of the office or on holiday.

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