Kibaniko hiki hakifanyi kazi vizuri, kwa hiyo mkate wa tosti unaungua haraka.

Because kibaniko belongs to the ki-/vi- noun class in Swahili, and words that describe or point to the noun have to agree with that class.

• singular: ki-
• plural: vi-

So:

• kibaniko hiki = this toaster
• vibaniko hivi = these toasters

The demonstrative hiki agrees with kibaniko. Using hii would be the wrong noun-class agreement here.

Hakifanyi is made of several parts:

• ha- = negative marker
• ki- = subject marker for a singular ki-/vi- noun like kibaniko
• fanyi = verb stem from -fanya = do / make

So hakifanyi literally means something like it does not do, where it refers to kibaniko.

In the full phrase:

• hakifanyi kazi = it does not work

This is a very common expression in Swahili.

In Swahili, -fanya kazi literally means to do work or to function/work.

So:

• inafanya kazi = it works / it is functioning
• haifanyi kazi = it does not work / it is not functioning

With kibaniko, the subject marker must match the noun class:

• kibaniko hiki hakifanyi kazi = this toaster doesn’t work

So even though English says work, Swahili often uses the idea do work / function.

Vizuri means well.

So:

• hakifanyi kazi = it doesn’t work
• hakifanyi kazi vizuri = it doesn’t work well

Even though vizuri looks like a plural adjective form historically, here it functions as an adverb, meaning well. Native speakers use vizuri very commonly after verbs:

• anasoma vizuri = he/she studies well
• gari linaenda vizuri = the car is running well

Kwa hiyo means therefore, so, or for that reason.

It connects the first idea to the result:

• Kibaniko hiki hakifanyi kazi vizuri = This toaster doesn’t work well
• kwa hiyo = so / therefore
• mkate wa tosti unaungua haraka = the toast bread burns quickly

It is a very common connector in both speech and writing.

Wa here is a connector of possession/association that often translates as of.

So:

• mkate wa tosti = bread for toast / toast bread / bread used for toasting

This pattern is very common:

• kikombe cha chai = cup of tea
• mlango wa nyumba = door of the house
• kitabu cha mwanafunzi = the student’s book / book of the student

Because mkate is in the m-/mi- noun class (singular), the connector appears as wa.

The verb has to agree with the subject noun, which here is mkate.

Mkate is in the m-/mi- noun class, and its singular subject marker is u-.

So:

• mkate unaungua = the bread is burning

Breakdown:

• u- = subject marker for singular mkate
• na- = present tense
• ungua = burn

So unaungua = it is burning.

Other subject markers would match different noun classes:

• kiti kinaungua = the chair is burning
• nyama inaungua = the meat is burning
• mtoto anaungua = the child is getting burned / burning

This is a very useful question.

• kuungua = to burn / get burned / be burning
• kuchoma = to burn something / roast / pierce / sting, depending on context

In this sentence, mkate wa tosti unaungua means the bread is burning / getting burnt, so kuungua is the natural choice because the bread is the thing affected.

Compare:

• Mkate unaungua. = The bread is burning.
• Kibaniko kinauchoma mkate. = The toaster is burning the bread.

So -ungua is more like an intransitive burn, while -choma is often transitive burn something.

Because Swahili usually builds tense and subject information directly into the verb.

Unaungua already contains:

• u- = it
• na- = present tense
• ungua = burn

So the meaning it is burning is already expressed in one verb word.

This is normal in Swahili:

• anasoma = he/she is reading
• kinavunjika = it is breaking
• zinaenda = they are going

You do not usually need a separate word like English is.

Swahili, like English, uses many loanwords. Tosti comes from English toast.

This is very common, especially for modern objects, foods, and technology. Swahili speakers may use loanwords naturally if they are widely understood.

So mkate wa tosti is a normal way to refer to bread meant for toasting or toast bread.

Yes, in many contexts you could simply say mkate if the meaning is obvious.

For example:

• Kibaniko hiki hakifanyi kazi vizuri, kwa hiyo mkate unaungua haraka.

That would still make sense as This toaster doesn’t work well, so the bread burns quickly.

But mkate wa tosti is more specific and helps show that we are talking about bread being toasted, not just bread in general.

Here haraka functions as an adverb, meaning quickly.

So:

• unaungua haraka = it burns quickly

Haraka is often used this way after verbs:

• anatembea haraka = he/she walks quickly
• gari linaenda haraka = the car goes fast

Depending on context, haraka can also be part of expressions relating to speed or urgency, but in this sentence it clearly means quickly.

Yes, sometimes a speaker could use ndiyo maana if they want to emphasize that is why.

For example:

• Kibaniko hiki hakifanyi kazi vizuri, ndiyo maana mkate wa tosti unaungua haraka.

This means roughly:

• This toaster doesn’t work well; that’s why the toast bread burns quickly.

Compared with kwa hiyo:

• kwa hiyo = so / therefore
• ndiyo maana = that is why

Both are natural, but kwa hiyo is a straightforward connector, while ndiyo maana can feel a bit more explanatory.

You would change the noun and all agreeing words to the plural vi- class:

• singular: Kibaniko hiki hakifanyi kazi vizuri
• plural: Vibaniko hivi havifanyi kazi vizuri

Breakdown of the plural changes:

• kibaniko → vibaniko
• hiki → hivi
• hakifanyi → havifanyi

If you continued the sentence, you might say:

• Vibaniko hivi havifanyi kazi vizuri, kwa hiyo mikate ya tosti inaungua haraka.

That means These toasters don’t work well, so the slices/loaves of toast bread burn quickly.

Yes, it is in the present tense.

You can tell from the tense marker -na- inside the verbs:

• hakifanyi → negative present form of -fanya
• unaungua → u-na-ungua

In affirmative verbs, -na- clearly marks the present:

• kinafanya = it is doing / it works
• unaungua = it is burning

In the negative present of many verbs, the form changes in a way learners often just memorize:

• kinafanya = it works
• hakifanyi = it does not work

So yes, the sentence describes a present, general situation: the toaster isn’t working properly, and as a result the bread burns quickly.