A kundli is a map of where the nine grahas stood when you were born, arranged around the point that was rising on the eastern horizon. The tool above draws it in either regional layout and lists every position to the arcminute.
Two things it does that most generators do not. It tells you which house system produced the chart, and it lists the planets a different one would move. And it checks whether your birth-time uncertainty is large enough that this is not really your chart at all.
What the chart is made of
Three ingredients, and only three.
The lagna, the degree of the zodiac rising on the eastern horizon at your birth moment. This is the origin the whole chart is measured from.
The nine grahas, being the Sun, Moon, Mars, Mercury, Jupiter, Venus, Saturn, and the two lunar nodes Rahu and Ketu. The nodes are not bodies; they are the two points where the Moon's orbit crosses the Sun's apparent path, which is why eclipses happen near them and why they are always exactly opposite each other.
The twelve houses, counted from the lagna.
Everything else on a chart is derived from those. The house lords, the dignities, the divisional charts, the dasha periods all come out of the same three inputs.
Whole-sign houses, and why that is a choice
Here is a decision every kundli generator makes and almost none discloses.
This page uses whole-sign houses. The first house is the entire sign holding the lagna. If your lagna is at 27° of Karka, the first house is all of Karka, from 0° to 30°, and a planet at 2° Karka is in the first house even though it sits twenty-five degrees away from the rising point.
That is what the D1 rashi chart is in the Parashari tradition, and it is what nearly every printed kundli shows.
The alternative is bhava chalit, where each house begins at the lagna's exact degree instead. With a lagna at 27° Karka, the first house would run from 27° Karka to 27° Simha, straddling two signs. A planet at 2° Karka would then fall in the twelfth house, not the first.
Same birth data, same astronomy, same planetary longitudes to six decimal places. Different house for the planet, and therefore a different reading.
The tool lists exactly which grahas in your chart the two systems disagree about. On some charts it is none. On charts with planets near sign boundaries it can be several.
Neither system is a mistake, and this is not a case where one site is broken. They answer different questions: whole-sign asks which sign a planet shares with the lagna, bhava chalit asks how far round the wheel it has actually travelled from the rising degree. If another site puts one of your planets in a different house from this one, check the house system before assuming anything is wrong.
The two chart layouts are not styles
North Indian and South Indian charts show identical data. They organise it in opposite ways, and confusing them will make you misread every placement on the page.
North Indian. The houses are fixed on the page. House 1 is always the top-centre diamond, house 2 the wedge to its upper left, and so on anticlockwise. Because the houses never move, the signs must, so a number is written in each house telling you which rashi it holds: 1 for Mesha through 12 for Meena. When you look at a North Indian chart, the position of a planet on the page tells you its house directly.
South Indian. The signs are fixed on the page. Meena is always top-left, and the grid runs clockwise through Mesha, Vrishabha and the rest around the border. Because the signs never move, the houses must, so the lagna has to be marked, conventionally with a diagonal stroke across its cell. Here the position of a planet tells you its sign directly, and you count round from the marked lagna to get its house.
The practical consequence is simple. On a North Indian chart, position means house. On a South Indian chart, position means sign. Reading one with the other's habit produces a chart that looks perfectly sensible and is wrong throughout.
Why your birth time matters more than you think
The planets barely move in an hour. The Sun covers a degree in a day. Saturn takes two and a half years to cross one sign.
The lagna covers a degree every four minutes.
So an hour of error in your birth time changes almost nothing about where the planets are, and changes the entire house framework they sit in. If the lagna moves to the next sign, all nine grahas move one house at once. Every one of them.
That is the specific danger of an approximate birth time. The chart does not look damaged. The positions are all still correct, the layout is still coherent, nothing on the page announces a problem. It is simply the wrong chart, and it will be read with the same confidence as the right one.
The page therefore asks how sure you are of the time and tells you whether the lagna is stable across that window. If it is not, it says so plainly and names both candidate signs, because at that point there is no useful reading to be had until the time is settled.
Exalted, debilitated, and one famous exception
The chart marks the classical dignities, which are mechanical: a table of signs and degrees, checkable against any text.
A graha is exalted in one specific sign, deepest at one specific degree, and debilitated in the sign opposite at the same degree. The Sun is exalted at 10° Mesha and debilitated at 10° Tula. The Moon at 3° Vrishabha. Mars at 28° Makara. Mercury at 15° Kanya. Jupiter at 5° Karka. Venus at 27° Meena. Saturn at 20° Tula.
There is a well-known peculiarity in that list worth pointing out, because it looks like an error and is not. Mercury is exalted in Kanya, which Mercury also rules. It is the only graha for which exaltation and rulership fall in the same sign. Anyone tidying up the table by "fixing" that has introduced a bug rather than removed one.
Rahu and Ketu are deliberately shown without an exaltation. Their signs are genuinely disputed between texts, Vrishabha or Mithuna for Rahu and Vrischika or Dhanu for Ketu, and this page would rather report nothing than manufacture a consensus that does not exist.
Reading the dignities without over-reading them
Two cautions about that table, since dignity is the part of a chart people latch onto fastest.
The first is that exaltation is a point, not a plateau. Saturn is deepest exalted at 20° Tula, which means Saturn at 20°01′ Tula is very slightly past its best and Saturn at 2° Tula is exalted in name while sitting eighteen degrees away from the actual point. The chart above therefore reports how far a dignified graha is from its exact degree rather than just stamping it exalted, because those are different situations wearing the same label.
The second is that six of the seven exaltation signs sit at fixed relationships worth noticing. Every graha's debilitation is exactly opposite its exaltation, which follows from the definition rather than from doctrine, so the two tables carry exactly the same information and there is nothing extra to learn from the second one. If a source presents debilitations as an independent list, it is padding.
Retrograde, and what the chart is actually saying
Several grahas will often be marked retrograde. That means they appear to move backwards against the stars, which is a perspective effect: the Earth is overtaking them on a faster inner orbit, and the apparent reversal is the same illusion as a slower car seeming to slide backwards as you pass it. Nothing physically reverses.
Rahu and Ketu are marked retrograde permanently, because the lunar nodes really do regress along the ecliptic, completing a backwards circuit in about 18.6 years. That is a genuine motion rather than an appearance.
One technical note that changes charts. The nodes can be computed as the mean node, a smooth average, or the true node, which oscillates around it. The two differ by up to about a degree and a half, which is enough to put Rahu in a different nakshatra and occasionally a different sign. This page uses the mean node, as most Indian practice does, and says so in the method block.
Why another site gives you a different chart
In order of how much difference each makes.
A different birth time. Twenty minutes is five degrees of lagna. Near a sign boundary that is a different chart entirely.
A different house system, as described above. Whole-sign against bhava chalit, moving individual planets between houses.
A different ayanamsa. Lahiri and Raman sit about 1.45° apart, so a planet within that distance of a sign boundary lands in a different sign. Switch the selector above to see whether any of yours are close enough to care.
A different time-zone treatment. For Indian births before 1955 this is a real trap: Bombay kept UTC+04:51 until then and Calcutta UTC+05:53:20 until 1948, and neither can be expressed by the standard time-zone database. A site applying a flat +05:30 to a 1950 Bombay birth is thirty-nine minutes out, which is nearly ten degrees of lagna.
Mean against true node, moving Rahu and Ketu by up to a degree and a half.
Every one of those is a stated choice rather than an accident, which is why this page names the ones it made.
There is also a class of difference that is not a choice at all, and it is worth separating out. Two sites using the same ayanamsa, the same house system and the same birth data should agree on a planet's longitude to within a few arcseconds, because the underlying ephemerides are all derived from the same modern solutions. If two charts differ by a whole degree on Jupiter, something is actually wrong somewhere rather than differently configured. Disagreements at the arcminute level are normal; disagreements at the degree level are a bug in one of the two.
Reading the chart you have been given
A practical order, if you are looking at a kundli for the first time and want to check it rather than interpret it.
Start with the lagna, because everything else is relative to it. Confirm the sign, and confirm that the birth time it was cast for is the one you actually believe. If the two charts you are comparing disagree here, nothing further is worth comparing.
Then check Rahu and Ketu. They must be exactly six houses apart and exactly 180 degrees apart, always, on every correct chart ever cast. If they are not, the chart is broken and you can stop. It is the fastest single sanity check available, and it costs nothing.
Then check the Sun against the date. The Sun's sidereal sign changes around the middle of each Gregorian month rather than at the start, so a mid-August birth puts the Sun in Simha or Kanya depending on the exact day. A Sun in the wrong sign for the season means the ayanamsa or the date is wrong.
Only after those three would it be worth looking at anything else.
What this page will not do
It will not tell you what any of it means.
There is no shortage of sites that will read a chart and tell you about your marriage, your career, your health or your enemies, usually with a remedy available for purchase at the end. This page computes positions and shows its working: the sidereal longitude of each graha, the degree within its sign, its nakshatra and pada, its house under a named system, and the dignities that follow mechanically from a table.
Every one of those numbers is checkable against an independent ephemeris, and if you disagree with any of them you can find out exactly where the disagreement starts. That is the whole offer. What a tradition builds on top of the arithmetic is a separate matter, and one this page takes no position on.