Postikodi imeandikwa hapa.

Because postikodi belongs to noun class 9 in the singular, and the verb has to agree with that noun class.

So imeandikwa breaks down like this:

• i- = subject agreement for class 9 singular
• -me- = perfect marker
• andik- = write
• -w- = passive
• -a = final vowel

So the i- is there because the subject is postikodi.

If it were plural, the agreement would usually change to zi-:

• Postikodi zimeandikwa hapa. = The postcodes have been written here.

-me- is a very common Swahili tense/aspect marker. It usually shows a completed action with a present result.

So imeandikwa can mean things like:

• has been written
• is written (in the sense that it is now in a written state)

That is why this form can sound a bit like both English has been written and is written, depending on context.

Because andika means write, while andikwa means be written.

So:

• imeandika would mean it has written
• imeandikwa means it has been written

In this sentence, the postcode is not doing the writing. It is the thing that has been written, so the passive form is needed.

Swahili often does not use separate helping verbs the way English does. Instead, a lot of that meaning is built directly into the verb.

In imeandikwa, several pieces of information are packed into one word:

• i- = what the subject is
• -me- = completed action / present result
• -w- = passive

So Swahili does not need a separate word for is or has been here. The verb already includes that information.

Because Swahili does not have articles like English the and a/an.

Whether postikodi means:

• a postcode
• the postcode

depends on context.

That is very normal in Swahili. Learners coming from English often expect an article, but Swahili simply does not require one.

It can mean either, depending on context.

A perfect passive like imeandikwa often suggests:

• the writing happened already, and
• the result is true now

So in English, you might translate it as:

• has been written here
• is written here

Both can be reasonable. English and Swahili do not always match one-for-one in tense choice.

Because that is a very natural place for it.

Hapa means here, and Swahili often places locative words like this after the verb:

• Postikodi imeandikwa hapa.

This is a neutral, ordinary word order.

You can move things around for emphasis in some contexts, but the version with hapa at the end is the most straightforward.

Yes. Many nouns in this class have the same form in singular and plural, so the noun itself may not change, but the agreement on the verb does.

Compare:

• Postikodi imeandikwa hapa. = The postcode has been written here.
• Postikodi zimeandikwa hapa. = The postcodes have been written here.

So the verb agreement helps show whether the noun is singular or plural.

You can add the doer with na:

• Postikodi imeandikwa na Asha hapa. = The postcode has been written here by Asha.

In passive sentences, na introduces the agent, similar to English by.

So:

• imeandikwa = has been written
• imeandikwa na Asha = has been written by Asha

It is a borrowed word, ultimately from English postcode/postal code.

That is very common in Swahili, especially for modern or administrative vocabulary. Even when a word is borrowed, it still behaves according to Swahili grammar, including noun-class agreement.

So although postikodi is a loanword, it still takes normal Swahili agreement:

• postikodi imeandikwa
• postikodi zimeandikwa