What is a merge conflict? How to resolve it on GitHub

You

Emma just messaged me in a panic. Her pull request #132 says "This branch has conflicts that must be resolved", and the merge button is grey. She thinks she broke the site.

Alex Tutor

Nothing is broken. A conflict blocks one merge and nothing else: main, the live site and Emma's work are all exactly as they were. The pull request just waits for someone to make a decision.

Here's how the two delivery pull requests look right now. The message is worded the way GitHub words it as of 2026.

Alex Tutor

Delivery pull requests in catchow/website

Rewrite delivery page copy#132
This branch has conflicts that must be resolved. Conflicting file: pages/delivery.md
Raise free-delivery threshold to 1000 UAH#133
Merged yesterday as commit 6f2c8a1

You

#133 is Daniel's threshold change from last lesson. One of its commits was called "Update delivery page text".

Daniel

That's the collision. I changed one sentence on that page: the free-delivery line. Emma rewrote the whole page, that sentence included. Git got two different versions of one line and refused to guess.

Alex Tutor

Question 1

Pull request #132 shows "This branch has conflicts that must be resolved". This means the delivery page on the live site is broken right now.

Open
Rewrite delivery page copy#132
This branch has conflicts that must be resolved

TrueFalse

Alex Tutor

Here's how Git merges. It finds the commit where the two lines of work split, their common starting point, and compares each side with it.

If only one side changed a spot, Git takes that change. If the sides changed different files, or different parts of the same file, Git combines them on its own. That's most merges.

Alex Tutor

content/delivery-copy and main todayBoth lines start from e7c3b19. Each highlighted commit changed line 12 of pages/delivery.md in its own way. The branch is now 1 ahead and 3 behind.

e7c3b19Add summer promo banner
f02a6d4Update FAQ answers
e19c3b7Rewrite delivery page copycontent/delivery-copy
8be2f70Add cat treats bundle
6f2c8a1Raise free-delivery threshold to 1000 UAH (#133)main

A merge conflict appears only when both sides changed the same lines, or lines right next to each other, in different ways. There is no rule for that case: which version wins is a decision, and Git leaves decisions to people.

Alex Tutor

Line 12 of `pages/delivery.md`, three versions

e7c3b19, the starting point:  Free delivery on orders from 800 UAH.
main, after #133:             Free delivery on orders from 1000 UAH.
content/delivery-copy:        Orders from 800 UAH ship free, right to your door.

Both branches changed the same line after the starting point, so Git stops and asks a person.

You

So Daniel changed the number and Emma changed the words. Neither of them did anything wrong.

Daniel

Right. Now compare it with my checkout story from March. My branch and the cookie bar touched different files, so Git merged them without a word, and the result was broken.

Alex Tutor

Keep both halves of that in mind. No conflict doesn't mean the result is right. A conflict doesn't mean anyone made a mistake.

Alex Tutor

Question 2

Since Emma's branch split from main, both sides have changed something. In which cases will GitHub report a conflict? Select all that apply.

Choose all that applyEmma edited pages/delivery.md; main changed config/prices.jsonBoth changed line 12 of pages/delivery.md, each in its own wayBoth changed line 12 to exactly the same textEmma edited the heading on line 3; main changed a note on line 40 of the same fileEmma edited a line in pages/returns.md; main deleted that file

Alex Tutor

Back to #132. Under the conflict message there's a Resolve conflicts button. It opens a simple editor right on GitHub, with the conflicting file already loaded.

You

Emma is sharing her screen and clicking it now. It looks like a plain text file with strange arrows in the middle.

Alex Tutor

`pages/delivery.md` in GitHub's conflict editor

## Delivery

<<<<<<< content/delivery-copy
Orders from 800 UAH ship free, right to your door.
=======
Free delivery on orders from 1000 UAH.
>>>>>>> main

Couriers deliver within one day in Kyiv.

The version from Emma's branch sits above the divider, the version from main below it. The heading and the courier line are outside the markers: nothing to decide there.

These are conflict markers. <<<<<<< opens the conflict and names the branch the upper version came from. ======= divides the two versions. >>>>>>> closes the conflict and names the other branch.

Everything outside the markers is settled. Only the part between the arrows waits for a human. And the markers themselves aren't text for the page: they have to go.

Daniel

Engineers see exactly the same markers in their code editor after running git merge in the terminal. Same arrows, different window.

You

Seven characters on each side. Somebody really wanted them impossible to miss.

Alex Tutor

Question 3

Match each part of the conflict in pages/delivery.md with what it means.

Tap an answer, then tap the row it belongs to. You can also drag.

<<<<<<< content/delivery-copy
=======
>>>>>>> main
Lines outside the markers

Answers left to place

You

Emma's first instinct: keep her version. It's her pull request, after all.

Alex Tutor

Then the page would promise free delivery from 800 UAH, while the cart makes it free only from 1000. Customers would pay for delivery the page called free.

You

And keeping Daniel's line throws away Emma's rewrite. So the right answer is neither: Emma's words with Daniel's number.

Alex Tutor

That's the heart of this lesson. A conflict isn't an error, it's a question: what did each person mean, and what should the page say now? Git can't answer that. You can.

Daniel

Honestly, this is where I need a PM. I can resolve any conflict technically. I can't know whether finance changed its mind again, or which wording marketing approved.

Alex Tutor

In the editor you can keep one side, keep both, or write something new. Here it's something new: one line built from both.

Alex Tutor

Question 4

The conflict in pages/delivery.md:

<<<<<<< content/delivery-copy
Orders from 800 UAH ship free, right to your door.
=======
Free delivery on orders from 1000 UAH.
>>>>>>> main

The threshold went up to 1000 UAH in #133 at finance's request, and marketing approved Emma's new wording. What should replace the whole block, markers included?

Choose one answerOrders from 800 UAH ship free, right to your door.Free delivery on orders from 1000 UAH.Orders from 1000 UAH ship free, right to your door.Both lines, one after the other, with the markers removed

Alex Tutor

Emma replaces the whole block with the agreed line: "Orders from 1000 UAH ship free, right to your door." The three marker lines go too.

Daniel

Check that twice. In the terminal nothing stops you from committing a leftover =======, and then it turns up on the live page. I've seen it happen. To other people, of course.

Alex Tutor

When the file is clean, Mark as resolved tells GitHub this file is settled. If several files conflict, you pick the next one from the list on the left and repeat.

You

Here there's only one. So the last button is Commit merge.

Alex Tutor

Right. Once Emma presses it, check the result the way a reviewer would: the pull request's Files changed tab should now show just Emma's rewrite, with 1000 in line 12 and no trace of 800.

Alex Tutor

Question 5

Put the steps for resolving the conflict in #132 on GitHub in order.

Tap an item, then tap where it should go. You can also drag or use the arrows.

You

What does Commit merge actually commit? And where?

Alex Tutor

A merge commit on Emma's branch, not on main. GitHub merges main into content/delivery-copy, with your decision inside. As of 2026 its message reads "Merge branch 'main' into content/delivery-copy".

Alex Tutor

After Commit mergeThe merge runs from main into the branch. content/delivery-copy now has everything from main plus Emma's rewrite; main itself hasn't changed.

e7c3b19Add summer promo banner
f02a6d4Update FAQ answers
e19c3b7Rewrite delivery page copy
8be2f70Add cat treats bundle
6f2c8a1Raise free-delivery threshold to 1000 UAH (#133)main
c90d4e7Merge branch 'main' into content/delivery-copycontent/delivery-copy

You

So the branch is zero behind now, and the conflict message is gone.

Daniel

And the merge button is back, waiting for my review. Since we squash, that merge commit never reaches main's history: main gets one clean commit for #132.

Alex Tutor

One more thing to read in that graph: which way the merge goes. Resolving a conflict on GitHub updates the pull request's branch. The site changes only when the pull request itself is merged.

Alex Tutor

Question 6

Someone resolved a conflict in pull request #145 with GitHub's editor. What does the highlighted commit b2 tell you?

Pull request #145 after a conflict was resolved on GitHub

a1Add about page
b1Rewrite our story section
a2Update team photos (#141)main
b2Merge branch 'main' into content/about-pagecontent/about-page

Choose one answerThe rewritten about page is already on the live sitemain's changes, together with the resolution, are now on the branch; main itself hasn't changed yetThe branch was squash-merged into mainCommit b1 was thrown away to make the conflict disappear

Alex Tutor

The web editor handles one kind of conflict: different edits to the same lines of a text file. That covers most conflicts in copy.

Other kinds need the command line: say one branch deleted a file the other edited, or both replaced the same image. As of 2026 GitHub then deactivates Resolve conflicts and says the conflict is too complex for the web editor.

Daniel

That's my job, not yours. But I'd still come to you with the same question: what should the result be?

Alex Tutor

So who resolves? Usually the author of the blocked pull request, together with the author of the change it collided with. The PM brings the answer to "what should it say?".

You

So my part: find out what each side meant, agree on the result, write the decision in the pull request and check Files changed afterwards.

Alex Tutor

And what not to do: pick a side just to turn the button green, resolve conflicts in code or config you don't understand, or edit someone else's branch without asking.

Alex Tutor

Question 7

A copy conflict blocks a pull request for a page you're responsible for. Which of these are part of a PM's job? Select all that apply.

Choose all that applyTell the author to keep their own version so the merge button turns greenFind out what each side intended, for example from the other pull request and its issueResolve a conflict in the checkout's JavaScript yourself, because the editor allows itWrite the agreed text and the reason in a pull request commentCheck Files changed after the resolution to make sure the page says what was agreed

Alex Tutor

Why did this one happen at all? Emma's branch lived for more than a week and rewrote a whole page. Meanwhile main moved on without it.

You

Three commits behind by now. On the branches page last time it was two.

Daniel

Each of those commits was a chance to collide. The longer a branch lives and the more it touches, the more main changes underneath it.

Alex Tutor

That's why this module keeps repeating the same habits: small branches, one task each, merged within days. And bring fresh main into a longer branch early, while conflicts are still small.

And talk. One line in the team chat, "I'm rewriting the delivery page this week", and Daniel would have pinged Emma before touching that sentence.

You

Which is a PM job too: knowing that finance and marketing are changing the same page in the same week.

Alex Tutor

Question 8

Which of these pull requests is most likely to run into a merge conflict?

Pull requests waiting to be merged

Fix typo on returns page#151
1 commit · 1 file · opened yesterday · 0 behind main
Add Halloween banner#152
2 commits · 2 files · 3 days old · 1 behind main
Update courier phone number#153
1 commit · 1 file · 2 days old · 2 behind main
Redesign all product pages#148
23 commits · 38 files · 6 weeks old · 41 behind main

Choose one answer#151 "Fix typo on returns page"#152 "Add Halloween banner"#153 "Update courier phone number"#148 "Redesign all product pages"

Alex Tutor

Last task. Daniel reviews #132 tomorrow, and he'll see a line that matches neither his version nor Emma's original.

Write a comment for the pull request: what line 12 says now and why. Two or three sentences.

Daniel

Mention where the 1000 came from. In a year somebody will run blame on that line, follow it to #132 and land right on your comment.

You

A note for the next detective. I know exactly how that feels.

Alex Tutor

Question 9Short answer · AI-checked task

Daniel will review pull request #132 tomorrow. Line 12 of pages/delivery.md now reads "Orders from 1000 UAH ship free, right to your door.", which matches neither his version nor Emma's original. Write a 2–3 sentence comment on #132: what the line says after the conflict was resolved, and why.

Write your answer and get a score with feedback from our AI reviewer.

Log in to get AI feedback

Daniel approved, Emma merged, and the delivery page now reads "Orders from 1000 UAH ship free, right to your door." That's module 2: branches, merges and the conflicts between them.

You

And the checkout fix? #134 has been a draft for a while now.

Daniel

Almost ready for review. Next module is all about pull requests, and you'll get to read mine tab by tab.

Alex Tutor

That’s the lesson. You answered every task — nicely done.

Next lesson: Anatomy of a pull request: tabs, description, checks