The activist was remanded in custody until a court hearing in five days' time. Police have not named Thunberg in the case.
A police statement said Ravi was a "key conspirator in the document's formulation and dissemination."
The "toolkit" document shared by Thunberg encourages people to sign a petition that condemns the "state violence" against the protesters. It also urges the government to listen to the protesters rather than mock them. It mentions different hashtags to use on Twitter to support the protests. Additionally, it asked for people worldwide to organize protests near Indian embassies or and domestically at government offices on February 13 and 14.
Delhi police said Ravi and her group had "shared" the toolkit with Thunberg.
The Bangalore-based activist is a founder of Fridays For Future India, which is part of an international protest network established by Thunberg to highlight climate change issues.
Tens of thousands of farmers have camped on the outskirts of India's capital, Delhi, for over two months, demanding a repeal of new agricultural laws that they say benefit private corporations.
Social media clampdown
Celebrities, including the singer Rihanna, Thunberg, the US lawyer and activist Meena Harris — the niece of Vice President Kamala Harris — and lawmakers in the UK and the United States have backed the farmers in posts on social media. The Indian government slammed them for endorsing the protests.
Following these posts, police launched an investigation into people accused of stirring "disaffection and ill will" against the government.
On Wednesday, Twitter suspended hundreds of accounts in India at the request of Prime Minister Narendra Modi's government, which has been trying to contain protests by clamping down on demonstrators' online activity.
Twitter stopped short of complying with demands to block accounts that belonged to activists, politicians and journalists, arguing that that would "violate their fundamental right to free expression under Indian law."
Rights groups 'worried' for Ravi's safety
Jairam Ramesh, an opposition lawmaker, called Ravi's arrest and detention "completely atrocious" and "unwarranted harassment and intimidation."
A coalition demanded Ravi's release and said activist groups were "extremely worried for her safety and well-being."
A friend of Ravi's wrote on Twitter on Saturday that the activist "needs a strong voice to get justice" with the hashtag #ReleaseDishaRavi.
What are the farmers' protests about?
In September, India's Parliament passed three agriculture bills aimed at liberalizing the country's farm sector. They were subsequently signed into law, sparking farmers to protest across the country.
The government argued that the new laws will give freedom to farmers to sell their produce outside regulated markets and enter into contracts with buyers at agreed prices.
The ruling Hindu nationalist Bharatiya Janata Party (BJP) insists that the laws will fetch better prices and free farmers from traditional middlemen who dominate the trade. The government hopes that its new policy will double farmers' income by 2022.
Farmer associations say the legislation does not guarantee the acquisition of produce at the minimum support price, thus leaving growers at the mercy of corporations that are now expected to enter the country's troubled farming sector.
In January, India's top court put the laws on hold and formed a committee to resolve the standoff.
Farmers have held huge rallies across the country in the past few years to protest the government's "neglect" of the agriculture sector and increasing privatization.
More than half of India's farmers are reportedly in debt, with 20,638 dying by suicide in 2018 and 2019, according to India's National Crime Records Bureau.
shs/mm (Reuters, AP, AFP, dpa)