Is it legally binding to write a guarantee?

Legal analysis: the letter of guarantee is the result of the civil subject's unanimous expression of will in law. As long as the agreed contents are not illegal, the responsibilities and obligations of the agreed matters are clear and have legal effect. The agreement is binding on both parties. If one party violates the agreement, the other party can take the agreement to court. If you are not at ease, you can go to the notary office for notarization. Or go to other places with relevant rights and obligations, and both parties shall jointly sign and affix the notarization seal. To be legally effective, a letter of guarantee must meet three conditions: 1, and the letter of guarantee is a true expression of one party's will; 2. The guarantee content does not violate the relevant provisions of laws and regulations; 3. The content of the guarantee does not violate the principle of public order and good customs.

Legal basis: Civil Code of People's Republic of China (PRC).

Article 502 A lawfully formed contract shall become effective upon its formation, unless otherwise provided by law or agreed by the parties.

In accordance with the provisions of laws and administrative regulations, if the contract should go through the approval procedures, such provisions shall prevail. If the failure to go through the formalities such as approval affects the effectiveness of the contract, it will not affect the performance of the obligation clauses such as approval and the effectiveness of relevant clauses in the contract. If the party that should go through the formalities for approval fails to perform its obligations, the other party may require it to bear the responsibility for violating its obligations.

The modification, assignment and dissolution of a contract shall be subject to the provisions of laws and administrative regulations, and the provisions of the preceding paragraph shall apply and shall be subject to approval.

Article 506 The following exemption clauses in the contract are invalid:

(1) Causing personal injury to the other party;

(2) Causing property losses to the other party due to intentional or gross negligence.