The Tondo Conspiracy of 1587, popularly known as the Conspiracy of the Maginoos (Spanish: La Conspiración de las Maginoos), also known as the Revolt of the Lakans, was a revolt planned by Tagalog nobles known as maginoos, led by Don Agustin de Legazpi of Tondo and his cousin Martin Pangan, to overthrow the Spanish government in the Philippines due to injustices against the Filipinos. It was territorially one of the largest conspiracies against the Spanish rule next to the Katipunan. It ranged from provinces near Manila all the way to the Calamianes Islands near Palawan.

Legazpi sought help from a Japanese sea captain named Juan Gayo who was a Christian and asked for arms and warriors to fight alongside them in exchange for one-half of the tributes collected in the Philippines. They also requested help from places such as Borneo, Laguna, and Batangas with a plan to assault the city of Manila and assassinate the Spaniards. However, their plan was discovered by the Spaniards when Magat Salamat revealed their plan to fellow rebel Antonio Surabao, who turned out to be a traitor when he reported the conspiracy to the Spaniards. Consequently, the rebels associated with the conspiracy were punished, with some being put to death and others being exiled. The plot against the Spaniards died alongside them.

Numerous datus were not in favor of the Spanish rule as they had conflicting interests with regard to authority and freedom. An instance of such is the waning obedience of the slaves to the datus. This was brought about by the initiatives of the Spaniards to abolish slavery in hopes of shifting the slaves' allegiance from the datus to the kingly Spaniards. Furthermore, this elimination of slavery had institutionalized how the slaves were obligated to pay their tributes to the Spaniards instead of the datus. They had been reduced to vassalage, thus the plan of rebellion of the datus against the Spaniards.

Martin Pangan, who was accused of adultery, Agustin de Legazpi, who was accused of not paying fees as governor of Tondo (his Bruneian Muslim name before Baptism to Catholicism was Rajah Muhammad Zahir al-Din), Gabriel Tuambasan, and Pitonggatan all met in jail, where they made a pact of the datus to aid each other in times of need and hardship. They also made a pact to stand united against the Spaniards, though they did not know in which manner yet.

After they got out of jail, Martin Pangan (who was exiled from Tondo) went to live in a village in Tambobong (known today as Malabon), where he, along with Legazpi, planned a secret meeting. They reached out to the datus of Pandacan, Navotas, Taguig, Maysilo, Catangalan, and many others in the Manila area and of nearby provinces such as Candaba, Pampanga who had been thinking of starting an uprising for quite some time then. With a pseudo reason of visiting their dear friend Pangan, arrived Agustin Manuguit and his father Felipe Salalila (chief from Maysilo), Magat Salamat (chief of Tondo), Pedro Balinguit (chief from Pandacan), Geronimo Basi and Gabriel Tuambasan (Legazpi's brothers), Luis Amanicalao and his son Calao, Dionisio Capolo (chief of Candaba) and his brother Felipe Salonga (chief of Polo), Felipe Amarlangagui (chief of Catangalan), Francisco Acta (another chief from Tondo), and Omaghicon (chief of Navotas). Timawas, servants, and other allies were also invited to the secret meeting.

All conspirators went planning for three days, pretending to be merely celebrating and drinking as they were keeping their planning under the covers. As they recalled the good old times before the Spanish conquest, they had strengthened their unified bond. Subsequently, they agreed that they would always protect each other and if the Spaniards' initiatives toward the freedom of the datus' slaves were reinforced, they would unite in preventing this to come into fruition.

Legazpi told his co-conspirators that he knew a Japanese captain of a trading boat named Juan Gayo, a Japanese Christian, whom he frequently entertained in his home. They were able to communicate through his interpreter, Dionisio Fernandez. Through him, the conspirators were assured of weapons they could use for the revolt. He also allegedly promised to provide them with Japanese warriors, under the deal that he would get a half of the tribute to be collected in the Philippines. The warriors were to arrive in Manila and pretend they arrived with peaceful intentions by bringing in ship flags for the Spaniards to use. Once they captured the Spaniards, Legazpi was to be made king. However, there was no fine print that dictated for how long this deal would go on, thus showing the lack of organization in the plan.

Legazpi also had ties with Brunei, as he was the son-in-law of the sultan. As such, the conspiracy also sought the help of Borneo. They believed they would come join and help the uprising not only because of their apparent blood ties, but because of their historical clash with the Christian Spaniards as well. The plan was that once Bornean fleets arrived at Cavite causing the Spaniards to call the chiefs to their aid, they would arrive with their men and attack the Spaniards in their own homes.