This article is currently under construction. As the subject is under active development, information here may not yet be final.

The Threat Assessment Index (TAI) is a standardized cataloging system used by the UNSC to rank the level of danger an organisation or group represents, such as rebel cells, colonial armed forces, and full-fledged polities. Maintained and updated by Section One of the Office of Naval Intelligence, it is intended to act as a simplified information repository for military planning, with the hope being to preemptively nullify competitors to the state. Although it is designed to directly compares their ability to fight the entire UNSC, the TAI can be scaled-down to be more applicable for localized arenas.

There are four known tiers that make up the index; grey, green, yellow, and red, in escalating order of threat. Prior to the 2553 Treaty revision, the TAI only determined the military capability these groups were determined to have. Since then, their known or suspected intent has also been factored in; this is because so many post-Covenant factions are able to effectively outgun the UNSC, and failed to inform larger strategic or diplomatic planning in a major way.

Level One

Also represented by the color green, Level One defines that an entity are unable to hurt or challenge the UNSC in military engagements, have shown actions that makes a military confrontation unlikely, or both. Surveillance priority is low, and few patrols, if any, are posted near the borders of 'green' polities.

Most post-Covenant War organizations that are classified in this level are either members of, or allied to the Concord of Reconciliation. In addition, planetary defense forces on most human colonies are also given this designation.

Level Two

Given the color yellow, Level Two defines that an entity has the ability to harm the UNSC or its interests. Such groups are generally large enough to require a substantial deployment of troops and resources to overcome, although it is still assumed that they are too weak to overcome a dedicated task force. Following the Treaty revision, Level Two has also been applied to nations that are equivalent in power to the UNSC, but have little desire to fight, at least in the short-term.

Level Two organizations encompasses most of the known Covenant polities, typically those too far away to care about humanity's presence. Larger independent human alliances, such as those in the Madara Fringe, are also included in this level.