Most SEOs and many casual searchers will have noticed something Google do when you search, often called query expansion or query rewriting. At its best, this is a useful feature that overcomes poorly contructed or ambiguous search queries. At worst it is a major annoyance, returning imprecise and irrelevant results for well-crafted and precise search keywords.

[For those in a hurry or in the know, here's the bookmarklet: Bypass query expansion. Drag it to your browser toolbar or folder, and then click it on a Google SERP. It will prefix your search keywords with a plus symbol and resubmit the search.]

I posted a series of observations on Google's query expansion capabilities about 12 months ago. Essentially, Google will adapt the search keywords you enter in order to match what they think you were searching for, as opposed to what you actually typed in. If you search Google for "car", it will match results for obviously related words like "cars" but potentially via other word relationships to things like "automobiles" or even individual car manufacturers.

Casual searchers will also benefit from the "did you mean" suggestions (and matches shown) for incorrect spelling, e.g. searching for "markting", which shows results for "marketing".

Unfortunately, for SEOs and advanced searchers, the behaviour is unhelpful. I searched earlier to day for programming-related keywords:

php curl ob_flush

This is a very specific query, and I was looking for something very specific. Here's the top few results:

I knew from experience that these were expanded results. The top result has nothing to do with the "curl" part ofthe query at all. Google has guessed that this part of my query was unnecessary. But Google was wrong.

The way to prevent much of Google's query expansion handling is to prefix search keywords with a plus symbol. So:

+php +curl +ob_flush

I now have a different (more relevant) set of results:

Over time, Google has moved more and more towards this type of expansion, and further and further away from what I, as an experienced searcher, want from my results. So I end up constantly typing plus symbols to get more precise and relevant results.

I decided enough was enough and wrote a simple browser bookmarklet to add a plus to each search keyword and resubmit the search form. Here's what to do:

• Drag this bookmarklet to your browser's bookmarks folder, or right click it and choose "bookmark", "add to favourites" or whatever wording your browser uses: Bypass query expansion
• On a Google results page for your query, click the bookmark
• Observe the change in results

Remember that this won't affect every search you do, and in addition will not get around some types of query-rewriting Google undertake.

For SEOs, you'll get much more precise results for research queries like site searches using this method. Keep an eye on the number of results too!