The three were given sentences of four months in prison, two of them suspended, and two were jailed immediately.
All three were arrested at some distance from the demonstration, the second protest against Israel’s offensive on Gaza that Paris police banned following clashes near a synagogue after a march on 13 July.
The two younger men, aged 18 and 24, were detained as they headed for the Marais area of Paris, where the 13 July violence took place.
One was found guilty of throwing a cardboard tube in the face of a riot police officer, causing him to take three days off work – a charge he denied, claiming to have been “overwhelmed by the events”.
The second, who told the court that he was a sympathiser of the far-right Front National, said he was heading for the Marais to “provoke the Jewish Defence League”, a right-wing group given to physical confrontation with those it judges anti-Semitic.
A bottle of white spirit was found in his bag but he said he did not touch it “when I saw there was conflict”.
The third, a 45-year-old with a criminal record, was arrested in the metro near the scene of the demonstration with two knives and teargas canister in his bag and claimed to have been on his way to a flea market but to have stopped off to take a look at the protest “out of curiosity”.
Police arrested 65 after a minority of protesters clashed with police at the end of the demonstration.
Forty-one were detained but charges were dropped against 21 of them.
The 20 remaining face charges ranging from being in possession of an illegal weapon to organising an unauthorised demonstration.