The question of whether the gospel of John is historical and true has been raised for quite some time now. Some even consider most of the 4th gospel to be fiction.

“Since the 19th century, scholars have almost unanimously accepted that the Johannine discourses are less likely to be historical than the synoptic parables and were likely written for theological purposes”—Wikipedia

There are obvious and striking differences between the Gospel of John and the Synoptic Gospels (Matthew, Mark and Luke). These include:

• John contains no narrative parables, no account of the trans­figuration,  no mention of Jesus’ temptations by Satan the devil and no report of Jesus casting out demons.
• John includes a vast amount of material not found in the syn­optic Gospels tradition, such as the records of extended conversations with Nicodemus, the Samaritan woman and the disciples, as well as of significant miracles (e.g., the turning of water into wine, and the resurrection of Lazarus).
• John recounts an extensive Judean ministry for Jesus, including several visits to Jerusalem, whereas the Synoptic Gospels focus on his Galilean ministry.
• Certain features of John’s presentation also raise seeming chronological difficulties for understanding Jesus’ action in the temple (John 2:13-22) and the precise sequence of events during the week of his death and resurrection.
• Perhaps most significant, notable stylistic differences emerge between Jesus in John, who discourses somewhat poetically on themes of light, life, witness and truth, and the synoptic Jesus, who argues forcefully and consistently on the theme of the kingdom of God.

The accumulation of these differences has generated speculation regarding the historical reliability of this document as a testimony concerning Jesus (John 20:31). There are, however, significant reasons for believing John to be historically accurate:

• In any attempt to assess the reliability of John, priority should be given to John’s own testimony about his purpose in writing. John alone among the Gospels provides an explicit statement of purpose: “Jesus performed many other signs in the presence of his disciples, which are not recorded in this book. But these are written that you may believe that Jesus is the Messiah, the Son of God, and that by believing you may have life in his name” (John 20:30,31 NIV). This purpose state­ment reflects the writer’s in­tention to present selective accounts of Jesus’ ministry: “Jesus did many other things as well. If every one of them were written down, I suppose that the whole world would not have room for the books that would be written (John 21:25 NIV), aimed at persuading the reader that Jesus of Nazareth really is the promised Messiah.
• The apostle was well aware, and freely admits, that Jesus did many other things, commenting at the close of his Gospel account, “Jesus also did many other things. If they were written down, I suppose the whole world could not contain the books that would be written” (John 21:25 NLT). Many of the apparent omissions by John are thus essentially acknowledged by John and, therefore, are not to be considered as evidence against the historicity of the book. He was selective in his recording of the events of Jesus’ life. However, the synoptic writers were also selective, in that they omitted many of the things John wrote about. A comparative analysis of John’s Gospel with the Synoptic Gospels makes it clear that John, probably writing about thirty years after the Synoptics, likely had the other three Gospels before him as he wrote his Gospel, and that he wrote to fill in some of the events that Matthew, Mark and Luke omitted. In fact, about 92% of John’s Gospel is unique.
• No other Gospel addresses the theme of truth as frequently as John’s. He used a series of signs and a parade of witnesses to rein­force the main thesis of his work. The trustworthiness of these witnesses, including John’s own explicit claim to have been an eyewitness is vital to his purpose: “The man who saw it has given testimony and his testimony is true”  (John 19:35 NIV); “this is the disciples who testifies to these things and who wrote them down. We know that his testimony is true” (John 21:24 NIV). This should remind readers that accuracy was very important to this apostle and writer, the apostle John.
• This concern for accurate reporting is reflected in the exact recording of numbers (John 2:20; 21:11); the translation of foreign terms (John 1:38; 20:16); and the precise depictions of persons, places and customs (John 2:16; 4:20; 5:2; 19:40).
• A close reading of John reveals numerous agreements with the Synoptic Gospels, in terms both of broad themes and of spe­cific details.
• Upon careful, close, examination, there are no actual contradictions between John’s gospel and the synoptic gospels.

Modern readers of John are wise to refrain both from over­stating the seeming contradictions and from excessive efforts at harmonizing John with the other Gospels. The fact is, John’s Gospel can be successfully harmonized with the other three Gospels, and this is often done in listings in chronological order the events in the gospels side by side careful . John accomplished his stated aim: to present an eloquent, “accurate” (John 21:24 NLT) and persuasive testimony “that Jesus is the Messiah, the Son of God, and that through this belief you may have life in his name” (John 20:30,31 NAB).

Objective Biblical evidence indicates the gospel of John is historical and true. God’s “word is truth” (John 17:17).

One source: New International Version Archaeological Study Bible