Learn Hardcore Indonesian: Sebuah rencana cadangan ditulis agar kualitas layanan tetap baik. - A backup plan is written so that the quality of service stays good.

With it: Sebuah rencana cadangan ditulis... = a single backup plan was written.
Without it: Rencana cadangan ditulis... = neutral/indefinite, also fine.
To stress the number 1: satu rencana cadangan.
“A certain/particular”: suatu rencana (cadangan).
To make it definite: rencana cadangan itu/tersebut.

Is “rencana cadangan” the right order? Why not “cadangan rencana”?

Yes. Indonesian noun compounds are typically head-first: rencana (head: “plan”) + cadangan (modifier: “backup”). Cadangan rencana would sound off or mean something like “a stock of plans.” Synonyms/near-synonyms:

rencana B (informal)
rencana darurat
rencana kontinjensi (formal/technical)

Why passive “ditulis”? How is it different from “menulis/menuliskan/dituliskan/tertulis”?

ditulis = passive (“is/was written”), focuses on the plan, not the writer.
menulis = active (“to write”).
menuliskan = active with -kan; often “to write something for someone / write something down,” adding an applied/benefactive nuance.
dituliskan = passive counterpart of menuliskan.
tertulis = “written/in writing” (state), e.g., rencana itu sudah tertulis.

Examples:

Active: Tim menulis sebuah rencana cadangan...
Passive: Sebuah rencana cadangan ditulis (oleh tim)...
Applied: Rencana itu dituliskan untuk klien.
Stative: Rencana cadangan itu sudah tertulis.

How do I include the agent (who wrote it)? Where does “oleh” go?

Add an “oleh”-phrase after the passive verb:

Sebuah rencana cadangan ditulis oleh tim TI. If the agent is a pronoun, many prefer “passive type 2” without “oleh”:
Rencana cadangan kami tulis agar... (patient + pronoun + bare verb)

Would “disusun/dibuat/dirancang” be better than “ditulis”? What’s the nuance?

Often yes:

disusun = drafted/structured; very idiomatic for plans.
dibuat = made/created; general.
dirancang = designed/planned; more technical/strategic.
ditulis highlights the act of writing it down. Example: Rencana cadangan disusun agar... sounds natural and formal.

What does “agar” mean here? How does it differ from “supaya/birar/untuk/sehingga”?

agar = so that/in order that (formal/neutral).
supaya = near-synonym, a bit more conversational.
biar = colloquial.
untuk = “in order to” but must be followed by a verb phrase, not a full clause.
sehingga = “so that/as a result,” expresses result, not intention.

Compare:

... ditulis agar/supaya/biar kualitas layanan tetap baik.
Not: ... ditulis untuk kualitas layanan tetap baik.
But: ... ditulis untuk menjaga/menjamin kualitas layanan tetap baik.
... ditulis sehingga... = “as a result,” different meaning.

Can the “agar” clause come first? Do I need a comma?

Yes: Agar kualitas layanan tetap baik, sebuah rencana cadangan ditulis. Use a comma when the purpose clause is fronted. When it comes last, a comma is usually not needed.

How does “kualitas layanan” work without “of”? Could I say “mutu layanan”?

Indonesian uses noun–noun compounds where English uses “of.” kualitas (head) + layanan (modifier) = “quality of service.” Common variants:

kualitas layanan
mutu layanan (more native-sounding)
kualitas/pelayanan and mutu/pelayanan also occur. Avoid heavy kualitas dari layanan unless needed for clarity or emphasis.

What does “tetap” mean, and where should it go?

tetap = remain/stay/keep (a state). It precedes the adjective/verb:

tetap baik, tetap tinggi, tetap berjalan. Nuance:
tetap = maintained despite potential change.
masih = still (hasn’t stopped yet).
terus = continuously/keep doing. Negation: tetap tidak baik (“remains not good”), not tidak tetap baik.

Is “baik” the best choice? What about “bagus” or “tinggi”?

baik collocates well with quality/service in formal/neutral tone.
bagus is more casual/colloquial; acceptable but less formal: kualitas layanan tetap bagus.
tinggi is used for measurable “high”: kualitas layanan tetap tinggi. Avoid tautology like kualitas yang berkualitas.

What’s the overall register? How would I say this more casually or more formally?

Current sentence is neutral–formal. Alternatives:

More formal: Rencana cadangan disusun agar kualitas layanan tetap baik.
Neutral active: Kami menyusun rencana cadangan supaya kualitas layanan tetap baik.
Casual: Biar kualitas layanan tetap bagus, kita bikin rencana cadangan.

Should “ditulis” be one word? What’s the rule with “di”?

Yes. di- as a verbal prefix attaches to the verb: ditulis, dibuat, dirancang. The preposition di (“at/in/on”) is separate: di rumah, di meja. So di tulis here would be incorrect.

How do I indicate tense/aspect (past/present/future)?

Indonesian is tenseless; add particles/adverbs if needed:

Past/completed: sudah/telah ditulis
Progressive: sedang ditulis
Future/intended: akan ditulis
Habitual: add sering, biasanya, etc.

How do I make it plural?

Use quantifiers; reduplication is possible but heavier.

Natural: beberapa/banyak rencana cadangan disusun...
Reduplication: rencana-rencana cadangan disusun...
With numbers: dua rencana cadangan disusun...

Is “agar supaya” okay? I see it in some texts.

You’ll see agar supaya in bureaucratic or older styles; it’s pleonastic. In modern, concise style, use either agar or supaya, not both.

Can I rewrite the purpose with “untuk + verb” instead of an “agar” clause?

Yes. Use untuk followed by a verb phrase:

Sebuah rencana cadangan ditulis untuk menjaga/menjamin kualitas layanan tetap baik. Don’t use untuk directly before a finite clause.

How do I make it definite/specific?

Add demonstratives or possessors:

Rencana cadangan itu/ini/tersebut ditulis...
Rencana cadangan perusahaan ditulis... (company’s backup plan)
Or keep passive and add agent: ... ditulis oleh tim operasional.

Is “Rencana cadangan kami tulis agar...” correct? It feels backwards.

Yes. That’s “passive type 2” with a pronoun agent:

Rencana cadangan kami tulis agar... ≈ Kami menulis rencana cadangan agar... This pattern is common with 1st/2nd-person agents and is perfectly natural.