The Liberal Democrats are asking 20,000 members what policies should be in the next general election manifesto.
Lib Dem members will get a 'sense of ownership', Mr Webb said
MP Steve Webb, running the web-based project, said it would help frame "detailed policy", but that the party would retain its core principles.
Subjects discussed so far include whether to scrap short prison sentences and how to reform inheritance tax.
Members of all parties were "fed up with being taken for granted", said Mr Webb, who is writing the manifesto.
The Liberal Democrat Manifesto Consultation site is open to the 67,000 party members, with 20,000 being emailed this week.
The aim is to produce an online manifesto at least several months before the next general election, which has to take place by 2010.
Mr Webb told BBC News: "It's about getting outside the Westminster bubble.
"What we've already done is have a consultation about our three broad themes, which we decided were freedom, fairness and greenness.
"It's not that we don't know what we think or stand for. It's saying we care about our broad principles, but how do they apply in certain situations.
"For instance, when it comes to inheritance tax, what is fair?"
The Conservatives are also carrying out detailed consultations, with several senior MPs leading working groups on areas such as the environment, the constitution and taxation.
The Lib Dem site allows party members to make suggestions, but Mr Webb said: "It is not a total free-for-all."
He added: "The feedback we are getting from members is very, very positive. Doing this early in the Parliament, rather than nearer the next election, gives our members a sense of ownership.
"If manifestos appear six weeks from an election, they are almost useless.
"As a small party it takes a long time to get a message across."
Mr Webb went on: "This isn't going to replace our conference. It might help shape what goes to the conference."
Research published last year by the Unlock Democracy group found 40% of Liberal Democrat associations had fewer than 100 members.
In general, local politics had "dwindled away to an unprecedented degree", director Peter Facey said, adding the public needed "a basic level of information during elections".
The report also said parties were in a "vicious circle", with policy-making becoming ever more centralised and alienating members.
Mr Webb, the former Lib Dem health spokesman, runs a weblog in his Northavon constituency, with more than 5,000 voters receiving email updates.
The manifesto website is being publicised on the My Space and Facebook sites.