Learn Hardcore German: Jedenfalls schreibe ich dir eine Kurznachricht, sobald ich losfahre. - In any case I will write you a short message as soon as I set off.

"Jedenfalls" is a sentence adverb meaning "anyway / in any case / at any rate." It often wraps up or refocuses a point. "Auf jeden Fall" means "definitely / for sure." In your sentence, "Jedenfalls" is more like "anyway"; using "Auf jeden Fall" would stress certainty: "I will definitely text you…"

Why is the verb "schreibe" right after "Jedenfalls"?

German main clauses are verb-second (V2). Whatever you put in first position (here: "Jedenfalls") is followed by the finite verb ("schreibe"), and the subject ("ich") comes after that: "Jedenfalls schreibe ich…"

Why is it "dir" and not "dich"?

Because "schreiben" takes a dative person (the recipient) and an accusative thing (what is written). So: "ich schreibe dir (DAT) eine Kurznachricht (ACC)." "Dich" would be wrong here.

Which case is "eine Kurznachricht," and why "eine" (not "einen")?

It's the direct object, so accusative. "Kurznachricht" is feminine (die). The feminine accusative singular article is "eine" (same form as nominative), not "einen" (which is masculine accusative).

Is "Kurznachricht" the normal word for a text message?

It’s correct and understood, but everyday speech more often uses:

"eine Nachricht" (a message)
"eine SMS" (still common)
"eine kurze Nachricht"
Brand-based: "eine WhatsApp" So "Ich schreibe dir …" often implies “I’ll message/text you” without naming it.

Do I need the comma before "sobald"?

Yes. "Sobald" introduces a subordinate clause, and German requires a comma before subordinate clauses. No comma after "Jedenfalls" in this sentence.

Why is "losfahre" at the end of the clause, and why isn’t it split?

"Sobald" is a subordinating conjunction, so the finite verb goes to the end of its clause. With separable-prefix verbs like "losfahren," the prefix stays attached in subordinate clauses: "… sobald ich losfahre." In a main clause it would split: "Ich fahre los."

Can I put the time clause first?

Yes: "Sobald ich losfahre, schreibe ich dir eine Kurznachricht." The comma remains, and the following main clause stays V2: "… schreibe ich …"

Could I say "werde schreiben" to talk about the future?

You can ("… werde ich dir … schreiben"), but German usually uses the present for near-future plans, especially with a time marker like "sobald." The present sounds most natural here.

Difference between "sobald," "wenn," and "als" here?

"sobald" = as soon as (immediate sequence)
"wenn" = when/whenever (general condition; less emphasis on immediacy)
"als" = when (one-time event in the past) So "sobald" is the best match for "as soon as."

Is "losfahren" the right verb? What about "abfahren," "wegfahren," or "losgehen"?

"losfahren" = set off/start driving (by vehicle) — best for you personally leaving by car.
"abfahren" = depart (often scheduled transport: trains, buses).
"wegfahren" = drive away/leave (focus on leaving a place).
"losgehen" = set off on foot.

Why "dir eine Kurznachricht" and not "eine Kurznachricht dir"?

In the German middle field, a pronoun object typically precedes a full noun: dative pronoun ("dir") before accusative noun ("eine Kurznachricht"). If both are pronouns, the usual order is accusative before dative: "Ich schreibe sie dir."

Can I just say "Ich schreibe dir, sobald ich losfahre" without naming the message?

Yes. That’s very idiomatic; "schreibe dir" already implies sending a message/text.

Any spelling or capitalization pitfalls?

"sobald" is one word (not "so bald").
"losfahren" is one word; in main clauses it splits (fahre … los).
Nouns are capitalized: "Kurznachricht."
"dir" is lowercase; the formal "Sie/Ihnen" would be capitalized.