Object Classes, or Containment Classes under the Anomaly Classification System, are categories of anomalous entities used by the Foundation as an organization tool. The classes are ranked by their difficulty to keep in containment. There are five main classes, in which the majority of entities are under: Safe, Euclid, Keter, Neutralized, and Explained, with Pending being a transitory class.
A common way to determine the class of an entity is to use an informal guideline called the Locked Box Test, which is a thought experiment consisting of imagining an anomalous object within a locked box and the result of leaving it alone.
Primary Classes[]
Safe[]

Emblem for the Safe classification.
The name of Safe was chosen as an easily understood term. Anomalies classified as Safe are those deemed as being easy to contain and generally safe to handle. While this does not mean Safe SCPs are not dangerous in some capacity, they pose no active threat to humanity or normalcy.
Using the Locked Box Test, if you lock an entity in a box and leave it alone, with nothing happening, it's likely Safe.
See Category:Safe for examples.
Euclid[]

Emblem for the Euclid classification.
The name of Euclid comes from the Greek mathematician Euclid. Anomalies classified as Euclid typically need more resources to keep fully contained, though this is mainly to a lack of full understanding of the anomaly. Most Euclid SCPs can move on their own, either possessing sapient or sentient capacities or simply being autonomous. Euclids can be dangerous, though not always.
Using the Locked Box Test, if you lock an entity in a box and leave it alone, and you're not sure what'll happen, it's likely Euclid.
See Category:Euclid for examples.
Keter[]

Emblem for the Keter classification.
The name of Keter is derived from the topmost part of the Tree of Life in the Jewish Kabbalah. Depending on headcanon, it could also be derived from Dr. Hermann Keter's name.
Anomalies classified as Keter require vast amounts of resources to contain or have common containment breaches; these entities generally have lengthy containment protocols and tend to have higher Risk Classes.
With the Locked Box Test, if you lock an entity in a box and leave it alone, and it breaks out, it's likely Keter.
See Category:Keter for examples.
Thaumiel[]

Emblem for the Thaumiel classification.
The name of Thaumiel comes from the order ruled by Satan and Moloch in the Jewish Kabbalah.
Under the Anomaly Classification System, Thaumiel entities are no longer a primary Containment Class, but instead a Secondary Class. As such, the description for Thaumiel will remain here, though it will be listed as a Secondary Class below. Anomalies classified as Keter possess properties that can be used to contain other, usually more dangerous, entities. Thaumiels are rare, with the high echelons of the Foundation knowing little about them.
Using the Locked Box Test, if it is the box, then it's likely Thaumiel.
See Category:Thaumiel for examples.
Neutralized[]

Emblem for the Neutralized classification.
Anomalies classified as Neutralized have had their anomalous properties removed, have been destroyed, or have been permanently killed. Neutralizing entities is generally frowned upon within the Foundation, with only very dangerous anomalies being given termination orders.
The Locked Box Test cannot be used because a Neutralized entity is dead, destroyed, or deemed normal.
See Category:Neutralized for examples.
Pending[]

Emblem for the Pending classification.
Anomalies classified as Pending are anomalies that have not been assigned a class. Pending SCPs generally do not have enough information at the time of an entry to facilitate an object class, likely being actively researched by the SCP Foundation in order to determine a proper class to place them in.
Using the Locked Box Test, the results may vary wildly.
See Category:Pending for examples.
Explained[]

Emblem for the Explained classification.
Anomalies classified as Explained are phenomena, objects, locations, or people who have been falsely classified as an SCP due to little understanding of that former anomaly. This could simply be due to mainstream science progressing to the point of discovering and explaining the Explained anomaly naturally, a hoax that had been debunked, or something falsely mistaken as an anomaly.
The Locked Box Test can't be used, as Explained SCPs would be considered non-anomalous and freed.
See Category:Explained for examples.
Esoteric[]

Emblem for the Esoteric classification.
Anomalies classified as Esoteric don't fit perfectly into any previous classes, instead possessing particularly unique attributes that require wildly different containment procedures and are handled much differently than other classes. That being said, Esoteric classes tend to pair with other classifications such as Euclid or Keter, as those are still relevant to an Esoteric anomaly.
There are many Esoteric classes, though the major ones are listed below.
See Category:Esoteric for examples.
Major Esoteric Classes[]
Apollyon[]

Emblem for the Apollyon classification.
The origin of the term Apollyon comes from the Greek version of Abaddon, the king of locusts.
Anomalies classified as Apollyon are so incomprehensibly powerful that containment is impossible or will soon become impossible in the future. Apollyon SCPs typically have high Risk and Disruption Classes, as many Apollyons are extremely dangerous and hostile to humanity.
See Category:Apollyon for examples.
Archon[]

Emblem for the Archon classification.
The term Archon is the Greek word for "ruler."
Anomalies classified as Archon are those that are best left uncontained, particularly due to keeping the Veil Protocol intact. Archon SCPs typically are intrinsically tied to humanity and/or consensus reality as a whole, which would make containment cause adverse effects as a result.
See Category:Archon for examples.
Cernunnos[]

Emblem for the Cernunnos classification.
Cernunnos derives from the horned god of Celtic mythology.
Anomalies classified as Cernunnos are those that can't be contained due to logistical or moral reasons. This differs from Archon in that the containment of Cernunnos SCPs would either bankrupt or weigh on the conscious of those who contain such an anomaly, while Archon SCPs being contained would likely take away from consensus reality.
See Category:Cernunnos for examples.
Decommissioned[]

Emblem for the Decommissioned classification.
Anomalies classified as Decommissioned were intentionally destroyed or de-anomalized by the SCP Foundation due to their danger, resource drain, or general inconvenience in keeping contained.
Out of universe, this was originally meant as a way to get rid of terrible entries to the SCP Wiki in-universe, typically by using author avatars, though later was used for normal SCPs for story purposes.
See Category:Decommissioned for examples.
Gödel[]

Emblem for the Gödel classification.
Gödel is named for Kurt Gödel, a logician known for his completeness theorem.
Gödel SCPs are those that can be explained by anomalous science.
See Category:Godel for examples.
Hiemal[]

Emblem for the Hiemal classification.
Hiemal is another word for wintry.
Hiemal SCPs are usually a pair of anomalies that keep each other in check by some means. As such, it typically means that more advanced containment procedures are not necessary, and simply must be contained to prevent any effects from harming the human race.
See Category:Hiemal for examples.
Principalis[]

Emblem for the Principalis classification.
Principalis is the Latin word for "primary."
Principalis SCPs typically are responsible for constituting the primary directive of the O5 Council.
See Category:Principalis for examples.
Tiamat[]

Emblem for the Tiamat classification.
Tiamat is the Mesopotamian goddess of the sea.
Containing a Tiamat SCP would require one to violate or completely abandon the Veil Protocol due to the sheer amount of force necessary to do so. This would inevitably result in a Broken Masquerade Scenario; though, in most cases, it would be preferable than to have a Tiamat entity be free.
See Category:Tiamat for examples.
Ticonderoga[]

Emblem for the Ticonderoga classification.
Ticonderoga is the anglicized spelling of the Mohawk word tekontaró:ken, meaning it is at the junction of two waterways.
For an SCP to be classified as Ticonderoga, it must both be impossible to contain and not needed to be contained. Ticonderoga was specifically created by the Classification Committee for SCP-4444, though it has gone on to be used to classify other SCPs as well.
See Category:Ticonderoga for examples.
Thaumiel[]

Emblem for the Thaumiel classification.
Thaumiel is the name of one of the Qliphoth in the Jewish Kabbalah.
Thaumiel SCPs are anomalies that are either directly beneficial to the Foundation or to humanity, or help keep another anomaly in check and contained.
See Category:Thaumiel for examples.
Uncontained[]

Emblem for the Uncontained classification.
Uncontained SCPs are anomalies that are currently not within Foundation custody or protection. They may have once been contained but have escaped by some means, or they have never been contained. This does not mean Uncontained SCPs are impossible to contain, it simply means they're not within the grasp of the SCP Foundation.
See Category:Uncontained for examples.
Yesod[]

Emblem for the Yesod classification.
Yesod is. according to the Kabbalah, the name of the foundation upon which God built the world.
Yesod SCPs are anomalies that have been integrated into the SCP Foundation's command structure.
Major Secondary Classes[]
Suffix System[]
The Suffix System for secondary classes helps indicate the attributes of an anomaly.
Impetus[]
Impetus is an English word meaning driving force.
SCPs bearing a "-impetus" suffix class indicates that the SCP is hostile.
Nuntii[]
Nuntii is a Latin word meaning "news."
SCPs bearing a "-nuntii" suffix class indicates that the SCP possesses memetic abilities.
Prodest[]
Prodest is a Latin word meaning "benefit."
SCPs bearing a "-prodest" suffix class indicates that the SCP has beneficial attributes.
Embla
A classification for SCPs that the Foundation uses to create other SCPs. The class is used once in Dr. Mann's Proposal, which is an entry in the SCP-001 hub.