The alternative to branching Dialogue Trees when it comes to interactive dialogue in video games: when talking to an NPC, instead of picking one of a handful context-sensitive lines to say, the player types in or otherwise inputs one of general keywords that the NPC can then react to.
If the keywords have to be typed in, the game may accept only specific keywords or employ a Text Parser to interpret proper language queries. Otherwise, the game tracks a global list of keywords that the Player Character knows and can bring up in dialogue at any time. In this case, new keywords may be highlighted in the dialogue window a la Rainbow Speak, and may even function like hyperlinks, letting the player immediately ask more about them with a mouse click.
The advantage of using keywords over Dialogue Trees is that the player is much more flexible in regards to topics that can be discussed with any NPC, who may know much more than is readily apparent. The drawbacks are that most NPCs will inevitably have nothing to say on most topics and the potential Sequence Breaking caused by players knowing more than their characters. It is also nigh impossible to simulate a normal human conversation this way, unless a powerful Text Parser is employed.
- In Façade, talking with Grace and Trip is accomplished by typing in what you want to say, with a powerful text parser deciphering and an producing an appropriate response from them.
- Dialogue in Syberia is facilitated by Kate's writing pad, wherein she collects relevant keywords and can interview each character she meets about them.
- In Lost Pig, conversation with the gnome occurs by typing tell gnome about [keyword] or ask gnome about [keyword]. The game automatically suggests new keywords related to topics the conversation has already covered, but the gnome will respond to any word the player enters.
- Non Player Characters in EverQuest have keywords in [brackets] that players need to [question] or try to respond to with [certain phrasing] to advance quest lines and [details].
- The Ultima series generally let the player type in the topic they want to discuss with an NPC when engaging them in conversation. Its Spiritual Successor, Shroud of the Avatar deliberately uses the same system.
- The first two Fallout games allowed the players to type in keywords freely in addition to Dialogue Trees that automatically came up when talking to an NPC.
- Wasteland 2, similarly to the Fallout series, tracks available keywords as pressable buttons in the dialogue window but also lets the player type them in manually.
- In The Elder Scrolls III: Morrowind, new keywords were highlighted as hyperlinks in the dialogue window and known keywords were listed to the right (slightly filtered by the NPC's affiliations and story purpose). In The Elder Scrolls IV: Oblivion, dialogue was fully voiced, so the keywords appeared in the list after they were spoken. In both games, NPCs could refuse to react to certain keywords if Relationship Values weren't high enough.
- The Exile series used keywords for conversation. The first two games required all keywords to be typed manually but the third game allowed players to click on words in the NPC's dialog as well as allowing manual typing and providing buttons for a few standard keywords (Buy, Sell, Name, Job).
- The Avernum remake of the series abandoned this in favor of Dialogue Trees.
- Final Fantasy II, oddly enough, uses these, and is the only entry in the series to do so.
- The fictional MMORPG in which the Noob franchise is set has a verbal variation. All media show players accepting a quest by telling "quest accepted" to a Quest Giver. The novels focus on this aspect a little more, the first one having Arthéon prononce the name of the Living MacGuffin as clearly as possible to every single Non-Player Character he runs into in hope of eliciting a reaction. The second novel had Sparadrap blurt out a string of potential keywords instead real sentences when short on time to get a Non-Player Character to follow him.