This is what Dr. Charles Burney wrote of Jommelli in Music in France and Italy:
"This morning I first had the pleasure of seeing and conversing with Signor Jommelli, who arrived at Naples from the country but the night before. He is extremely corpulent, and, in the face, not unlike what I remember Handel to have been, yet far more polite and soft in his manner. I found him in his night-gown, at an instrument, writing. He received me very politely, and made many apologies for not having called on me, in consequence of a card I had left at his house, but apologies were indeed unnecessary, as he was but just come to town, and at the point of bringing out a new opera, that must have occupied both his time and thoughts sufficiently. He had heard of me through Mr. Hamilton. I gave him Padre Martini´s letter, and after he had read it we went to business directly. I told him my errand to Italy, and showed him my plan, for I knew his time was precious. He read it with great attention, and conversed very openly and rationally, said the part I had undertaken was much neglected at present in Italy, that the Conservatorios, of which, I told him, I wished for information, were now at a low ebb, though formerly so fruitful in great men. He mentioned to me a person of great learning, who had been translating David´s Psalms into excellent Italian verse, in the course of which work, he had found necessary to write a dissertation on the music of the ancients, which he had communicated to him. He said this writer was a fine and subtle critic, had differed in several point with Padre Martini, had been in correspondence with Metastasio and had received a long letter from him on the subject of lyric poetry and music, all which he thought necessary for me to see. He promised to procure me the book, and to make me acquainted with the author. He spoke very much in praise of Alessandro Scarlatti, as to his church music, such as motets, masses and oratorios, promised to procure me information concerning the Conservatorios, and whatever else was to my purpose, and in his power. He took my direction, and assured me that the instant he had got his opera on the stage, he should be entirely at my service. Upon my telling him that my time for remaining at Naples was very short, that I should even then have been on the road in my way back home, but for his opera which I so much wished to hear, that besides urgent business in England, there was great possibility of a war, which would keep me a prisoner on the continent. He in answer to that and with great appearance of sincerity, said, if after I returned to England, anything of importance to my plan occurred, he would not fail of sending it to me. In short, I went away in high good humor with this truly great composer, who is indisputably one of the first of his profession now alive in the Universe, for were I to name the living composers of Italy for the stage, according to my idea of their merit it would be in the following order: Jommelli, Galuppi, Piccini and Sacchini. It is, however, difficult to decide which of the two composers first mentioned, has merited most from the public, Jommelli´s works are full of great and noble ideas, treated with taste and learning, Galuppi´s abound in fancy, fire and feeling, Piccini has far surpassed all his contemporaries in the comic stile, and Sacchini seems the most promising composer in the serious."