Стоит мне открыть окно, как кошка сразу прыгает на подоконник.

This is a fixed Russian pattern meaning as soon as I... , ... immediately happens or the moment I... , ....

So:

Стоит мне открыть окно, как кошка сразу прыгает на подоконник.

literally feels like:

It only takes me to open the window, and the cat immediately jumps onto the windowsill.

But in natural English, it means:

As soon as I open the window, the cat immediately jumps onto the windowsill.

This structure often suggests a regular, almost automatic reaction.

Because the construction стоит кому + infinitive uses the person in the dative case.

So:

• мне = to me / for me
• not я = I

In this pattern, Russian does not say I open in the normal way. Instead, it is more like:

• Стоит мне открыть... = It only takes me to open...

Other examples:

• Стоит тебе позвонить, как он приходит.
  As soon as you call, he comes.

• Стоит ей начать, как все замолкают.
  As soon as she starts, everyone falls silent.

Открыть is the perfective infinitive, and that fits well here because the sentence refers to a single completed trigger event:

• open the window → that action happens
• then the cat reacts

The pattern стоит кому + perfective infinitive often focuses on the action as a completed event that sets something else off.

Here, открыть окно means to open the window as one whole action.

If you used открывать, it would sound less natural here because открывать is imperfective and usually describes process, repetition, or general activity rather than the single event that triggers the next action.

In this construction, как introduces the result or immediate following action.

So the pattern is:

• Стоит мне открыть окно, как...
• As soon as I open the window, ...

This как does not mean the usual how here. It is part of the fixed expression.

You can think of the whole structure as:

• Стоит X, как Y
• No sooner does X happen than Y happens
• As soon as X happens, Y happens

Прыгает is imperfective present, and here it describes a habitual / repeated reaction:

Whenever I open the window, the cat immediately jumps onto the windowsill.

Russian often uses the present tense this way for things that regularly happen.

If you said прыгнет, that would be perfective future and would sound more like a single specific future event:

• If I open the window, the cat will jump...

But the original sentence is about a repeated pattern, so прыгает is the natural choice.

Because прыгать на подоконник expresses movement onto something, so на takes the accusative case:

• подоконник = accusative singular

Compare:

• кошка прыгает на подоконник = the cat jumps onto the windowsill
  movement toward a destination

• кошка сидит на подоконнике = the cat is sitting on the windowsill
  location, so на takes the prepositional case

This is a very common Russian contrast:

• куда? (to where?) → на + accusative
• где? (where?) → на + prepositional

Сразу means right away, immediately, or at once.

It strengthens the idea that the cat reacts without delay:

• как кошка сразу прыгает...
• the cat immediately jumps...

The sentence would still work without сразу, but сразу makes the cause-and-effect feeling stronger and more vivid.

It is perfectly normal Russian, but it is a bit more bookish/stylish than the most basic everyday way of saying the same thing.

A more neutral conversational version might be:

• Как только я открываю окно, кошка сразу прыгает на подоконник.
• Когда я открываю окно, кошка сразу прыгает на подоконник.

The стоит... как... pattern is very common and natural, but it has a slightly expressive flavor, often implying:

• immediate consequence
• predictable reaction
• “every single time”

Yes, Russian word order is flexible, but the original order is very natural.

Original:

• Стоит мне открыть окно, как кошка сразу прыгает на подоконник.

Possible variation:

• Стоит мне открыть окно, как сразу кошка прыгает на подоконник.

But that sounds less natural in neutral speech.

You could also say:

• Как только я открываю окно, кошка сразу прыгает на подоконник.

In the original sentence, the word order helps the sentence flow clearly:

1. trigger: Стоит мне открыть окно
2. immediate result: как кошка сразу прыгает на подоконник

Not in this sentence, even though стоить often means to cost.

Here, стоит is part of the idiomatic construction стоит кому-то сделать что-то, как...

So you should not interpret it as money or price.

Compare:

• Книга стоит 500 рублей.
  The book costs 500 rubles.

• Стоит мне открыть окно, как кошка прыгает...
  As soon as I open the window, the cat jumps...

Same verb, different meaning because of the structure.

Yes, depending on context.

Because the second clause uses прыгает (a habitual present), the whole sentence can imply repeated behavior:

• Whenever I open the window, the cat immediately jumps onto the windowsill.

At the same time, the structure стоит... как... strongly emphasizes immediacy, so as soon as is also a very good translation.

So both ideas are present:

• whenever = repeated habit
• as soon as = immediate reaction

That is why this Russian sentence feels especially vivid.

Yes. The sentence presents opening the window as the clear trigger for the cat’s action.

It does not just say two things happen in sequence. It suggests:

• I open the window
• that immediately causes or prompts the cat to jump onto the windowsill

This cause-and-effect feeling is one reason the стоит... как... structure is used.