Mumsnet is massive. It gets more than 30 million hits a month and 25,000 new posts appear on its talkboards every day. During the last election, politicians fell over themselves to be interviewed by its users in live chat sessions. Mumsnetters were to the 2010 election what Mondeo man was in 1997, the swing voters seen as the key to power.

They were also fearsome and raucous and could sometimes seem like an angry mob. Gordon Brown was rounded on for failing to name his favourite type of biscuit; Ed Miliband  climate change secretary at the time  for choosing disposable nappies over reusable cloth ones. This January, the mother of a disabled child wrote a despairing post about the government's refusal to ring-fence the funds allocated for respite care. Her story made the newspapers' front pages. She had reason to expect something to be done, since after a previous exchange on Mumsnet David Cameron had paid her a visit.

Mumsnet has political clout, then, but it's also an anarchic forum for advice-trading on all kinds of parenting dos and don'ts, from the seismic ("Don't give up work for your children") to the trivial (don't get killed in a fight over a parent-and-child parking space at the supermarket). The Mumsnet Rules  in a money for old rope sort of way  is a huge compendium of tips and anecdotes taken from postings on the site. It follows on from the Mumsnet guides to pregnancy, babies and toddlers, but aims more ambitiously to tell you about anything that might matter to any parent.

This means, confusingly, that advice about how to cope with your child's first day at infant school follows on from the material on how to find the best place to educate your hoodie teenager. There is, amusingly, a section dedicated to how to go cold turkey on the internet, including browsing on Mumsnet, in order to pay more attention to your child. The question of how much and what kind of attention to pay  whether over-parenting is a crime  is a recurring theme and a cause of much anxiety.

But for all the apparent haphazardness, the book  and the site  does have a message and a mission. Many of the entries are arguments in favour of common sense, against the baby manuals and experts (primarily the detested Gina Ford) who dictate that strict routines, regulated nap times and a well-ordered household are crucial. You should trust your instincts. You can't be perfect. You don't have to make fairy cakes if you don't want to or feel you have to give your child a bath every single night.

Several of the entries refer back to the writer's own childhood in order to reassure readers that the fun a child will remember having had  "the day the neighbours went water-skiing leaving a casserole in the oven and the oven caught fire"  has nothing at all to do with the unattainable perfection recommended by lifestyle journalists.

There's a pleasing homespun air about some of the tips  "a good wheeze" is to get your child to make his own Top Trumps so that the hours you spend playing with them are slightly less mind-numbing  and an appealing straightforwardness about some of the lines taken: "Do not forget that breastfeeding 'advice' given in many routine guru books is pants."

In response to the question of whether it's acceptable not to reciprocate on play dates, one user helpfully says: "I rarely had kids over. I don't like them much."

This reassuring, no-nonsense approach  keep doing what you're doing, don't feel too guilty  is presumably the main reason for Mumsnet's huge success, ever since the site was founded 11 years ago by two media professionals who met at an antenatal class. But it also presents something of a paradox: if there are no rules that matter, then why exactly are we reading The Mumsnet Rules?

Mumsnet is massive. It gets more than 30 million hits a month and 25,000 new posts appear on its talkboards every day. During the last election, politicians fell over themselves to be interviewed by its users in live chat sessions. Mumsnetters were to the 2010 election what Mondeo man was in 1997, the swing voters seen as the key to power.

They were also fearsome and raucous and could sometimes seem like an angry mob. Gordon Brown was rounded on for failing to name his favourite type of biscuit; Ed Miliband  climate change secretary at the time  for choosing disposable nappies over reusable cloth ones. This January, the mother of a disabled child wrote a despairing post about the government's refusal to ring-fence the funds allocated for respite care. Her story made the newspapers' front pages. She had reason to expect something to be done, since after a previous exchange on Mumsnet David Cameron had paid her a visit.

Mumsnet has political clout, then, but it's also an anarchic forum for advice-trading on all kinds of parenting dos and don'ts, from the seismic ("Don't give up work for your children") to the trivial (don't get killed in a fight over a parent-and-child parking space at the supermarket). The Mumsnet Rules  in a money for old rope sort of way  is a huge compendium of tips and anecdotes taken from postings on the site. It follows on from the Mumsnet guides to pregnancy, babies and toddlers, but aims more ambitiously to tell you about anything that might matter to any parent.

This means, confusingly, that advice about how to cope with your child's first day at infant school follows on from the material on how to find the best place to educate your hoodie teenager. There is, amusingly, a section dedicated to how to go cold turkey on the internet, including browsing on Mumsnet, in order to pay more attention to your child. The question of how much and what kind of attention to pay  whether over-parenting is a crime  is a recurring theme and a cause of much anxiety.

But for all the apparent haphazardness, the book  and the site  does have a message and a mission. Many of the entries are arguments in favour of common sense, against the baby manuals and experts (primarily the detested Gina Ford) who dictate that strict routines, regulated nap times and a well-ordered household are crucial. You should trust your instincts. You can't be perfect. You don't have to make fairy cakes if you don't want to or feel you have to give your child a bath every single night.

Several of the entries refer back to the writer's own childhood in order to reassure readers that the fun a child will remember having had  "the day the neighbours went water-skiing leaving a casserole in the oven and the oven caught fire"  has nothing at all to do with the unattainable perfection recommended by lifestyle journalists.

There's a pleasing homespun air about some of the tips  "a good wheeze" is to get your child to make his own Top Trumps so that the hours you spend playing with them are slightly less mind-numbing  and an appealing straightforwardness about some of the lines taken: "Do not forget that breastfeeding 'advice' given in many routine guru books is pants."

In response to the question of whether it's acceptable not to reciprocate on play dates, one user helpfully says: "I rarely had kids over. I don't like them much."

This reassuring, no-nonsense approach  keep doing what you're doing, don't feel too guilty  is presumably the main reason for Mumsnet's huge success, ever since the site was founded 11 years ago by two media professionals who met at an antenatal class. But it also presents something of a paradox: if there are no rules that matter, then why exactly are we reading The Mumsnet Rules?