必要がある・ 必要はないneed to; no need to
必要 is a noun, "need". 必要がある says there is a need to do something, and 必要はない says there is none. Both state it as a fact, without ordering anyone.
need to
The contents need to be checked once more before they are sent overseas.
no need to
There is no need to hurry. The deadline is next week.
With a verb
Verb dictionary form + 必要がある/必要はない
行く必要がある, 行く必要はない. Polite あります, ありません. The verb stays plain.
With a thing
Thing + が + 必要だ
お金が必要です, "I need money". Not needed: 予約は必要ありません, "no booking is needed".
Need a thing, need to do something
English "need" is a verb. 必要 is not, so a thing and an action are built differently.
You need a visa.
A thing: it takes が, and 必要だ ends the sentence.
You need to get a visa.
An action: the plain verb, then 必要がある.
Not said: ビザを
(You need a visa.)
The thing you need takes が, not を.
必要がある: it has to be done
This is how instructions, offices and doctors put it, and how you explain what a situation calls for.
For safety, the power needs to be turned off before starting work.
Does this document also need to be submitted?
For your own everyday errands it is heavy. In conversation people say ないと.
I have to go to the bank.
To yourself, or to a friend.
I need to go to the bank.
Correct, but it sounds like a report.
必要はない: there is no need
This one is common in conversation too, often to put someone at ease. 必要がない means the same. To tell someone not to bother, people mostly say 必要はない. In casual talk the particle often drops.
The procedure is simple. There is no need to ask a specialist.
You don't need to apologize.
There is no need to take off your shoes in this room.
You don't need to hurry so much.
Do I need to come tomorrow as well?
No, there's no need.
その必要はありません is a set reply: "that won't be necessary".
Close neighbours
なくてもいいN5
"It's fine not to." The everyday, softer way to take a duty away.
You do not have to hurry that much.
なければならないN5
"Must": a rule, or something you can't get out of. 必要がある only says the situation calls for it.
In the library, you must turn off your cell phone.
ことはないN3
Advice not to bother, or not to worry. Warmer than 必要はない.
There's no need to worry about it all by yourself.
Check yourself
1"You need a ticket."
チケット
Choose an answer to see why.
2"You need to book."
予約する
Choose an answer to see why.
3A doctor says this. What does it mean?
この
Choose an answer to see why.
More detail
必要はなかった
In the past it covers both "didn't need to, and didn't" and "didn't need to, but did". Only the rest of the story says whether the thing was done.
In the end, there was no need to pay an additional fee.
Noun + の必要
A noun for an action can come before it with の, mostly in writing.
The venue is too small, so a change is needed.
On signs: 不要
The short opposite on signs and forms is 不要: 予約不要, "no booking needed".
More sentences
There is no need to decide everything today. Let's check the priorities first.
Since this material is for internal use, there is no need to translate it into English.
The number of users has grown, so more server capacity is needed.
I rushed to take a taxi, but I would have made it by train too, so I didn't need to take one.