Legal analysis: the handwritten commitment letter is valid. The effectiveness of the letter of commitment depends on: the will of the parties is true and does not violate the principle of voluntariness; The actor has corresponding capacity for civil conduct; Do not harm the interests of the state, the collective or the third party; Do not violate the law, do not violate public order and good customs.

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

Article 5 Civil subjects engaged in civil activities shall follow the principle of voluntariness and establish, change and terminate civil legal relations according to their own wishes.

Article 7 Civil subjects engaged in civil activities shall follow the principle of honesty and credit and abide by credit.

Article 8 of the Civil Code of People's Republic of China (PRC)

Civil subjects engaged in civil activities shall not violate the law or public order and good customs.

Article 143 A civil juristic act that meets the following conditions is valid:

(1) The actor has corresponding capacity for civil conduct;

(2) the meaning is true;

(three) does not violate the mandatory provisions of laws and administrative regulations, and does not violate public order and good customs.