The website sprang into life shortly before 10am, after teasing visitors with a "stand-by" notice for the previous 12 hours. In a recorded message, Mr Forbes said: "Today, I'm happy to announce the beginning of my campaign" and described it as "a national crusade to restore Ronald Reagan's vision of hope and prosperity for all Americans".
Practically all the presidential candidates (and many congressional candidates) have their own websites, but Mr Forbes is the first to use it for his declaration.
Boasting news of his campaign "first, fast and unfiltered", the website said that Mr Forbes was offering "a dramatic reform agenda to defend America's economy, security and values" and prepare every child to "compete and succeed in the information age economy".
Mr Forbes is the fourth Republican to announce formally a presidential bid, but another six have already made it clear that they are in the running, including the two favourites, George W Bush and Elizabeth Dole. While these two have outlined priorities and programmes that tend towards the Republican centre, Mr Forbes, 51, has moved, if anything, further to the right since his last campaign - coupling his former tax-cutting zeal with a firmer moral pitch.
Mr Forbes, who spent $32m (pounds 20m) on his last campaign, is a proponent of the idea of a "flat tax", which would set a single, low, income and sales tax rate and abolish most concessions and allowances.
In theory, this is designed to make the tax burden fairer, but its opponents argue variously that it would penalise the poor, require too high a basic tax rate to be attractive, and minimise the redistributive function of taxation.
A firmer moral dimension to his campaign could also dilute Mr Forbes' appeal, driving some supporters away and failing to attract new ones.
Even if taking the high moral ground gives a Republican candidate an advantage, candidates like the Christian conservative, Gary Bauer, already hold that constituency and are unlikely to cede it.