After a while, you tend to get a "feel" for where terraformables can exist around certain star types. The conditions you need for terraformability are:
- In the "Goldilocks zone" of the star system - that is, the planet has to be in an orbit where the surface temperature can be between 260 K and 320 K, if the planet were to be given an Earth-like atmosphere. The current surface temperature of the planet isn't necessarily a reliable indicator, as the current atmosphere may be making the planet considerably hotter or colder.
- Planet must be Metal Rich, High Metal Content, Rocky, or Water World. Other planet types are not terraformable (and "metal rich terraformable" is extremely rare).
- Surface gravity must be between 0.40 and 1.99 Earth-gravities.
And that's it. If it ticks all those boxes, then it should come up as terraformable. There are a few anomalies around moons and co-orbiting planets, where a planet "ought to be" terraformable but isn't, or vice-versa. But other parameters that you might think ought to be important, such as the current atmospheric composition, presence of surface water, presence or absence of volcanism, presence or absence of moons, axial tilt and orbital eccentricity, are all considered irrelevant for terraforming purposes.