Earlier this month, rumors spread that Russian troops had pierced Ukrainian defensive lines along a critical section of the eastern front. Soldiers spoke of night infiltrations, gunfire rattling in the distance and skirmishes near villages once considered secure.

The rumors quickly reached Ruslan Mykula and Roman Pohorilyi, the Ukrainian co-founders of DeepState, the group behind what has become the definitive online map charting battlefield movements. After a day of digging, the two men confirmed that the breach was real, and worse than initially thought, with Russian troops pushing nearly 10 miles forward.

“There was a very big problem,” Mr. Pohorilyi said in an interview, adding that Ukraine’s defenses in the area had been at risk of crumbling.

The pair knew that updating the map with the Russian advance would be politically explosive. With peace talks heating up, publicizing the breach risked weakening Ukraine’s hand in the negotiations. At the same time, it could force Kyiv’s top military command, which had so far been muted about the advance and seemingly slow to grasp its severity, to respond decisively.

On the evening of Aug. 11, they updated the map and posted a long message on social media explaining the “quite chaotic” situation. Screenshots of the map showing two long Russian incursions that looked like rabbit ears spread like wildfire in Ukraine, and the military, after initially downplaying DeepState’s assessment, quickly deployed elite troops to contain the breach.

“It drew a lot of attention,” Mr. Pohorilyi, a bespectacled 26-year-old, said with a smile.

DeepState’s revelations about the Russian advance illustrate just how central its map has become to Ukraine over three and a half years of war. The map receives some 900,000 views daily on average. Among its viewers are civilians living near the front, trying to gauge if Russian troops are closing in; military experts and reporters tracking the shifting battle lines; humanitarian volunteers organizing evacuation plans; and even soldiers trying to cut through the fog of war.

“It’s kind of the go-to map in Ukraine,” said Rob Lee, a military expert at the Foreign Policy Research Institute. An avid user of the map himself, he posts its updates every week on X.

The popularity of DeepState shows how technology is reshaping the way war is chronicled. Geolocated combat footage streamed by soldiers on social media has become a key resource for mappers, while satellite internet available even in frontline hot spots lets troops send tips about breakthroughs almost instantly. Where a few decades ago it would take days for army reports or journalists’ dispatches to reach the public, Ukrainians now check DeepState when they wake up.

But the map’s high profile has also placed its creators in the cross hairs of war propaganda. Some Ukrainian commanders, worried about reprisals from their superiors, have pressured DeepState not to show lost positions.

Maintaining its independence — and, by extension, its credibility — in such a fraught environment is “very difficult,” Mr. Pohorilyi said. He emphasized again, “Very difficult.”

Concerns like these were far from Mr. Pohorilyi’s mind when he and Mr. Mykula launched DeepState in 2020. Back then, it was just a hobby, a Telegram channel where two childhood friends, one a law student and the other working in marketing, shared news on world affairs. They chose the name DeepState to lend the project an air of intrigue.

But as Russian troops massed at Ukraine’s border in 2021, they pivoted to monitoring the buildup. Moscow called it a drill and later announced a withdrawal. But the satellite images and videos the pair pored over told a different story. Equipment had been left behind, a sign that the troops would return.

In early 2022, as evidence of an impending invasion mounted, they hired people to assist with open-source research and prepared for the worst. On the first day of Russia’s invasion, they launched the map.

The map’s design is straightforward. Russian-seized territory is shaded red; zones retaken by Kyiv’s forces are green; and areas where control is contested because of ongoing fighting are gray. Small red squares mark Russian units, while arrows indicate their movements. (DeepState does not show Ukrainian positions to protect the safety of operations.)

More than 100 volunteers or employees work for DeepState to update the map every day, with the entire operation funded through donations.

As the war has dragged on, the videos that the group scours have become less reliable, with both sides exploiting images for propaganda. Mr. Mykula pointed to examples of Russian soldiers being filmed raising a flag in a village, which suggested they had seized it, only to get killed in Ukrainian counterattacks.

To fill in the gaps, DeepState cross-checks information with Ukrainian soldiers on the ground. “We know a lot of people on the frontline, in different military units,” Mr. Mykula, 30, said, adding that these sources number in the hundreds. The team never rushes to publish updates, waiting to be confident in its information, he said. But Mr. Mykula acknowledged that mistakes occasionally occur.

Mr. Lee, the military expert, also noted that the omnipresence of drones targeting anything that moves at the front had created vast no-go zones, making the picture of who controls what even murkier. In such an environment, he said, DeepState’s method of combining geolocated videos with verification from human sources “gives you a better sense of how accurately you can portray things.”

DeepState is so trusted that civilians near the front use the map to gauge danger. If the battle lines are 15 miles away, they are relatively safe from the drones swarming the battlefield, but not from Russia’s larger guided bombs, or KABs, which can strike much farther.

Earlier this year, Volodymyr Zrazhevsky, the mayor of Mezhova, a small town near the eastern front, was hunched over his office table, studying a printed DeepState map. He had marked it with circles to determine whether his town lay within the range of Russian bombs.

“First, we check DeepState. Second, we gauge the threat of a KAB strike on our town,” he said in a February interview. The Russians have since drawn closer to Mezhova, and residents have begun evacuating.

Perhaps the most unexpected users of DeepState’s map are Ukrainian soldiers themselves.

The Ukrainian military has its own internal battlefield map, called Delta. But soldiers say units sometimes do not report territorial losses to avoid blame, leaving the Delta map incomplete. Acknowledging the issue in a recent interview with the Ukrainian news outlet RBC-Ukraine, Gen. Oleksandr Syrskyi, Ukraine’s top military commander, said DeepState offered a critical complementary view.

“It’s a source of information that often helps to obtain data about the threat of losing a position,” General Syrskyi said.

His comments, which came after DeepState revealed the Russian breach in the eastern Donetsk region, near the city of Dobropillia, were a rare official recognition of the map’s value. More often, Ukraine’s leadership pushes back against map updates showing Russian advances in politically sensitive areas, such as a recent incursion that marked Russia’s entry into a new Ukrainian region, Dnipropetrovsk.

DeepState, Mr. Mykula said, acts as a counterbalance to the military’s omissions and spin. Without its alert about the breach near Dobropillia, he believes military reinforcements might not have arrived in time, potentially leading to a “catastrophe.”

Soldiers largely endorse this role as a check and balance. “I fully support this approach,” said Vitalii Piasetskyi, chief sergeant in Ukraine’s 93rd Brigade, “because there are indeed problems with reports on the real state of affairs in the areas of responsibility of some units.”

There is only one scenario where DeepState withholds updates: when the soldiers themselves request it to protect their operations. The most notable example is Ukraine’s surprise offensive in the Kursk region of western Russia last summer. DeepState held off on updating its map for the first two days of the offensive to maintain the element of surprise and prevent the Russians, who also track the map, from getting clues on where to strike back.

Mr. Pohorilyi said that “the safety of our military” comes first and that his group shared the same goal: winning the war.