Google unveiled a new tool on Wednesday which allows notes and comments to be posted alongside Web pages for others to read.

“Google Sidewiki” appears as a narrow pop-up browser panel on the left hand side of a website and displays messages from users about the content of the page.

The messages are visible to other users of Sidewiki who visit the site and they can post their own comments, but they cannot edit the comments of others.

A website about museums in New York city, for example, would have a Sidewiki panel featuring relevant notes and comments from other visitors.

Google, in a blog post, said Sidewiki was a way for Web users to contribute “insights” and “helpful information” next to any Web page.

The Internet search and advertising giant said it had developed an algorithm to ensure that the “most useful, high-quality entries” are displayed at the top of a Sidewiki panel.

Sidewiki is a feature of Google Toolbar for Firefox and Internet Explorer browsers and Google said it will be available soon for Google Chrome, its own Web browser.

Google Sidewiki is similar to other services launched in the past and it met with mixed reviews from technology bloggers.

Ars Technica said Sidewiki was “intriguing” but “it’s unclear if the service will really deliver a lot of value” and it could end up being “little more than a glorified comment system.”

PaidContent.org said Sidewiki “may anger some online publishers who have commenting systems of their own that they’d prefer visitors continue to use.”

A blogger for TechCrunch said he does not have high hopes for Sidewiki.

“Marking up the Web has limited appeal to the average consumer,” he wrote.