Mayor de Blasio swept into office promising a new era of transparency and good government — but thousands of e-mails released under court order show it was all a facade.

De Blasio had no choice, but he still tried to claim credit for sharing the e-mails of his exchanges with outside advisers, calling it a “pretty rare thing in public life.”

He is right about one thing: The document dump offers an unprecedented look at how de Blasio operates when he thinks no one is watching or will ever find out.

And what the messages reveal is a mayor obsessed with his image, determined to lift his national profile, and as thin-skinned as they come when it comes to the critics and the press.

De Blasio’s dreams of parlaying his 2013 mayoral win into a national platform began before he even got around to naming commissioners to run his agencies.

Just six days into his term, the mayor was ready to make plane reservations after receiving an unsolicited invitation to speak at the Ohio Democratic Party.

“This intrigues me, although I’m generally going to be VERY modest, local and travel-adverse this year,” de Blasio wrote. “But Ohio is the center of the political universe and I love it there.”

His skeptical advisers elected to indulge the new mayor, rather than shut down the idea as nuts.

“Ohio — gotta think about that one,” chimed in John Del Cecato, whom de Blasio regularly consulted for advice. “Yes, very important state[,] but I worry a bit about the optics.”

De Blasio ended up not going.

But his ambitions grew. He ventured to Nebraska, Iowa and California in 2015, hoping to transform himself into a kingmaker on the Democratic left.

Meanwhile, the homeless crisis was growing and a lead-paint scandal at the New York City Housing Authority was about to explode.

His own advisers — including longtime pal Patrick Gaspard — remained unconvinced of his national strategy.

After receiving a copy of a liberal political platform de Blasio planned to back to shift the Democratic Party to the left, Gaspard offered a lukewarm response.

“I’m still not clear what the coalition is and who exactly will be the muscle behind this,” he wrote. “What’s the win? The politics elude me.”

De Blasio also planned a presidential forum in Iowa in 2015 — it went nowhere.

Hillary Clinton and Bernie Sanders never agreed to attend, leaving de Blasio to spin the fiasco as part of a larger win.

“We started April 2 at Gracie Mansion (say that, imho [in my humble opinion]) and we have continued to grow,” de Blasio wrote, after nixing his aides’ advice. “We are replacing the forum with a new grassroots effort in Iowa and beyond, starting immediately.”

‘THE budget will take care of itself,” wrote Del Cecato the day before City Hall released de Blasio’s $78 billion spending plan for 2016.

The budget is arguably the most important document a mayor produces, but de Blasio was needed for something far more urgent, Del Cecato said: making phone calls to drum up support for “The Progressive Agenda.”

Del Cecato was one of five advisers de Blasio declared “agents of the city” in an attempt to shield his office’s e-mails.

In the choice between the nitty-gritty work of government and partisan politics, it was no contest.

City Hall staffers devoted considerable effort to promoting de Blasio’s wife, Chirlane McCray, who is looking to run for public office.

The mayor urged his aides to get McCray on MSNBC when word began to circulate that state Senate Republicans might attack her.

“Let’s release the tiger,” he wrote on Oct. 13, 2014.

When the City Hall press corps, known as Room 9, proved too hard-bitten for the first lady’s charm offensive, de Blasio’s team came up with a plan to circumvent them.

“We’ve broadened out the First Lady’s more directly at audiences via consumer outlets [like Univision] and [to] bypass Room 9 as necessary,” then-Director of Communications Andrea Hagelgans wrote on May 26, 2015. “We’ve also been doing podcasts and creating our own content.”

Not even heart-wrenching tragedy was safe from exploitation.

“I strongly believe Chirlane should call today for mental health screenings for all pilots,” de Blasio wrote in March 2015, after a suicidal pilot slammed a German jetliner into the French Alps and killed everyone onboard. “I am going on instinct here. My advice: don’t scrub too much or hesitate too much, just strike while the iron is hot.”

The mayor’s habits — especially his perpetual lateness — were a constant source of frustration to his aides.

In 2015, then-senior de Blasio aide Elana Leopold wrote a message titled “Help please” to let the mayor’s political ad man, director of communications and his official photographer know that her habitually tardy boss was “running late.”

Leopold also said that de Blasio “wants breakfast” and “would like an oatmeal with raisins and skim milk and double expresso (sic) w 4 sugars from starbucks if there is one or somewhere else.”

“Can someone get- pretty please??” she begged on May 12, 2015.

Communications chief Andrea Hagelgans responded within a minute to the 7:21 a.m. request.

“Though I am opposed to 4 sugars,” she wrote.

“Ya I cringe ever time I have to get,” Leopold promptly wrote back.

Beyond the naked ambition, de Blasio’s big dreams have been waylaid by scandal and authenticity questions as his rhetoric often fails to match his actions.

De Blasio has long fashioned himself as a defender of New York’s workers, backing moves to increase the minimum wage, establish family leave and give restaurant employees new protections.

But the exchanges show he treats his own staff with disdain, belittling close aides for small mistakes, pointing blame elsewhere and often refusing to heed advice.

The mayor ripped his aides after learning his speech at Manhattan’s Riverside Church in 2014 would be limited to 15 minutes.

“I will make do, but it won’t be a good a speech,” de Blasio wrote to his consultants and aides, before tossing them under the bus: “We need to set ground rules up front, or be ready to move if people switch up on us. I need a better, more thorough approach next time [please].”

In an exchange from 2015, de Blasio tore into his staff for preparing “bloodless” remarks for a Brooklyn church speech because it failed to play up his push to impose extra taxes on expensive homes.

“I did my own THANG at church. [Please] give me feedback on my remarks,” the peeved Mayor wrote afterward, before complaining about the venue, Bedford-Stuyvesant’s Concord Baptist Church of Christ.

“Next time we need a more energetic church,” de Blasio sniffed. “I could have named 10 convenient locations where we could have gotten a lot more emotion and support from the crowd for our friends in the media to see.”

Bill de Blasio ran in 2013 promising to be the most transparent mayor in history.

He turned out to be the most thin-skinned.

Since taking office, Hizzoner’s response to stories about scandals, failed plans and staff turnover has been to attack the critics and the press.

In one exchange, de Blasio instructs his staff to blow off questions from The Post, which joined with NY1 to successfully sue for the e-mails.

“As we’ve often said: let’s not give answers to the NY Post. Let’s say that via an exclusive with a reporter we like,” de Blasio wrote in a September 2015 e-mail.

The New York Times reporters at City Hall and the broadsheet’s liberal editorial page weren’t spared, either.

De Blasio labeled one-time Times City Hall Bureau Chief Michael Grynbaum as a “bad person” in an e-mail about a largely positive story.

And Hizzoner assailed the Gray Lady’s editorial board for twice turning down his op-eds, even though his own staffers advised they were not the sort of thing the Times typically prints.

“It just dawned on me how totally f–ked up it is that The Times has turned down the only 2 op-eds I’ve offered in 16 months, both on very weighty topics,” de Blasio screeched in one e-mail.

He assailed a reporter from Vanity Fair for a story that chronicled his early political troubles and vowed to never do another magazine profile.

“The journalist blatantly lied to us and he has a horrible grasp of the facts,” de Blasio raged. “This was a ridiculous waste of our time, and we shouldn’t’ fall for this trick again.”

He added: “Only trust those who have proven themselves to us.”