The best California ballot measures state clear intentions and leave little or no room for debate over how they will be implemented.

Gov. Jerry Brown’s initiative to roll back fixed prison terms for non-violent felons fails this basic test. Vote no on Proposition 57 on the November ballot.

We agree with the governor’s intent, but the proposition is sloppily written. It fails to clearly identify which crimes would fall under it and how an inmate’s criminal history would affect eligibility for parole. Brown or other reform advocates need to try again

Proposition 57 is another attempt to deal with the fallout from California’s tough on crime movement that followed the murder of 12-year-old Polly Klaas in 1993 by an ex-convict. Mandatory sentencing was broadly instituted. One result was massive overcrowding in prisons and skyrocketing costs to taxpayers.

In 2011, the Supreme Court stood firm in saying that California prison conditions constituted cruel and unusual punishment. The court ordered the state to reduce its prison population by more than 30,000 inmates. The governor has been looking for the best way to comply ever since. The state moved lower-level felons to county jails, and in 2014 voters passed Proposition 47 to reduce the penalties for some drug and property offenses.

Prop. 57 is designed to make about 7,500 non-violent prisoners eligible for early release. Proponents expect that the state parole board would actually release only about 750 inmates who have worked to rehabilitate themselves and exhibited good behavior. This could motivate other inmates to take advantage of rehab opportunities.

It’s a good idea, but the details matter.

Most California district attorneys oppose Prop. 57 because its definition of violent crimes is far too narrow. It fails to specify some offenses — arson, hostage taking — that should make convicts ineligible for consideration. It’s a matter of debate whether some sex crimes, including rape, would be included.

It also muddies the distinction between convicts who are in jail for the same offense, but have vastly different criminal histories. Inmates whose records indicate they’re a public safety risk shouldn’t have the same access to early release as, say, first offenders.

Reformers say all this can be fixed when regulations are written to implement the law, but that’s asking voters to take too much on faith. Proponents say Brown won’t let bad things happen, but he’ll be gone in two years.

California has to find more ways to reduce prison overcrowding and costs. Money that now goes to prisons could be far better spent on crime-solving or prevention. Early release for some offenders is a reasonable idea, but the strategy has to be clear. Prop. 57 is not good enough. Vote no.