Team Validation

Before a battle starts, Frontier checks every team against the ladder’s format rules. Species bans, move restrictions, custom MoLang logic — it all runs through the clause system. Illegal teams can’t queue.

When Validation Runs

Clauses are enforced at three different points, depending on their type:

1. Queue join — TEAM_VALIDATION clauses run against the player’s team. Fail any clause and you can’t join the queue. The failure message tells you exactly what’s wrong.
2. Battle start — SHOWDOWN_NATIVE clauses are passed to the Showdown engine as rule strings. Format-level bans (species, moves, abilities, items) are also applied here.
3. During battle — IN_BATTLE clauses fire when players attempt to use banned mechanics (Mega Evolution, Terastallization, etc.).

Note

Team validation runs again at battle start, not just at queue join. This catches edge cases where a player’s team state changed between joining the queue and the match starting.

Three Clause Types

Type	When it runs	How it works
TEAM_VALIDATION	Queue join + battle start	Custom MoLang expressions evaluated against the team.
SHOWDOWN_NATIVE	Battle start	Rule string passed directly to the Showdown battle engine.
IN_BATTLE	During battle	Frontier intercepts banned battle mechanics (gimmick bans).

Clause Structure

Clauses live in config/frontier/clauses.conf. Here’s an example:

clauses {
    species_clause {
        displayName = "Species Clause"
        description = "A player cannot have two of the same species on their team."
        type = "TEAM_VALIDATION"
        showdownRule = "Species Clause"
        perPokemon = false
        molangExpression = ["!query.has_duplicate_species"]
        failureMessage = "Species Clause: Your team has duplicate species"
    }
}

Field	Type	Default	Description
displayName	String	""	Human-readable name shown in GUIs.
description	String	""	What the clause does, shown in format info.
type	ClauseType	"SHOWDOWN_NATIVE"	When and how the clause runs.
showdownRule	String?	null	Showdown rule string (only for SHOWDOWN_NATIVE clauses).
molangExpression	List	null	MoLang expressions for validation. Each entry is a separate expression.
perPokemon	Boolean	true	If true, expression runs once per Pokemon. If false, once for the whole team.
failureMessage	String?	null	Message shown when validation fails. Supports {pokemon} (per-Pokemon only) and {clause} placeholders.

Format-Level Bans

Beyond clauses, formats can ban specific species, moves, abilities, and items directly. These are configured in config/frontier/formats.conf:

formats {
    ou {
        displayName = "OU"
        clauses = ["species_clause", "sleep_clause", "evasion_clause", "ohko_clause"]
        bannedSpecies = ["mewtwo", "arceus", "zacian"]
        bannedMoves = ["swagger", "baton_pass"]
        bannedAbilities = ["moody", "shadow_tag"]
        bannedItems = ["kings_rock"]
        validateLegality = true
    }
}

Field	Type	Default	Description
bannedSpecies	List	[]	Species to ban (Showdown IDs, e.g. "mewtwo", "arceus").
bannedMoves	List	[]	Moves to ban (e.g. "swagger", "baton_pass").
bannedAbilities	List	[]	Abilities to ban (e.g. "moody", "shadow_tag").
bannedItems	List	[]	Items to ban (e.g. "kings_rock").
validateLegality	Boolean	false	Check each Pokemon’s moves and abilities against its species/form for legality.

Formats also support inheritance with the includes field — ban lists and clauses merge from all included formats:

formats {
    base_ou {
        clauses = ["species_clause", "sleep_clause", "evasion_clause", "ohko_clause"]
        bannedSpecies = ["mewtwo", "arceus", "zacian"]
        validateLegality = true
    }
    ou_no_tera {
        displayName = "OU (No Tera)"
        includes = ["base_ou"]
        clauses = ["ban_tera"]
    }
}

Built-In Clauses

Team Validation Clauses

ID	Name	Per-Pokemon	Description
species_clause	Species Clause	No	No duplicate species on a team.
item_clause	Item Clause	No	No duplicate held items on a team.
evasion_clause	Evasion Clause	Yes	Bans Double Team and Minimize.
ohko_clause	OHKO Clause	Yes	Bans Fissure, Sheer Cold, Horn Drill, Guillotine.
monotype	Monotype	No	All team members must share a type.
level_cap	Level Cap	Yes	Pokemon must be at or below the format’s target level.
no_legendaries	No Legendaries	Yes	Legendary Pokemon are banned.
nfe_only	NFE Only	Yes	Only unevolved Pokemon (Little Cup).

Showdown Native Clauses

ID	Name	Showdown Rule	Description
sleep_clause	Sleep Clause	"Sleep Clause Mod"	Only one opposing Pokemon can be asleep at a time.

In-Battle Clauses (Gimmick Bans)

ID	Name	What it bans
gimmick_ban	Gimmick Ban	Mega Evolution, Ultra Burst, Z-Moves, Dynamax, Terastallization
ban_mega	Mega Evolution Ban	Mega Evolution, Ultra Burst
ban_tera	Terastallization Ban	Terastallization
ban_dynamax	Dynamax Ban	Dynamax
ban_zmoves	Z-Moves Ban	Z-Moves

MoLang Query API

Frontier exposes MoLang queries for writing custom clause expressions.

Per-Pokemon Queries

Available when perPokemon = true. Access through query.pokemon.

Query	Returns	Description
query.pokemon.level	Double	Pokemon’s current level.
query.pokemon.can_evolve	1.0/0.0	Whether the Pokemon can still evolve.
query.pokemon.has_move('name')	1.0/0.0	Whether the Pokemon knows a specific move (Showdown ID).
query.pokemon.has_any_move('m1,m2,...')	1.0/0.0	Whether the Pokemon knows any of the listed moves (comma-separated).
query.pokemon.species.has_label('label')	1.0/0.0	Whether the species has a label (e.g., legendary).
query.pokemon.ability.name	String	The Pokemon’s ability (Showdown ID).

Team-Wide Queries

Available in both per-Pokemon and team mode.

Query	Returns	Description
query.team_size	Double	Number of Pokemon on the team.
query.has_duplicate_species	1.0/0.0	Whether the team has duplicate species.
query.has_duplicate_items	1.0/0.0	Whether the team has duplicate held items.
query.team_shares_type	1.0/0.0	Whether all team members share at least one type.
query.format_target_level	Double	Format’s target level (0 if none set).
query.format_team_size	Double	Format’s max team size.

Custom Clause Examples

Ban specific abilities

clauses {
    no_uber_abilities {
        displayName = "No Uber Abilities"
        description = "Bans Shadow Tag and Arena Trap."
        type = "TEAM_VALIDATION"
        perPokemon = true
        molangExpression = [
            "query.pokemon.ability.name != 'shadowtag' && query.pokemon.ability.name != 'arenatrap'"
        ]
        failureMessage = "{pokemon} has a banned ability"
    }
}

Level 50 cap

clauses {
    max_level_50 {
        displayName = "Level 50 Cap"
        description = "All Pokemon must be level 50 or below."
        type = "TEAM_VALIDATION"
        perPokemon = true
        molangExpression = ["query.pokemon.level <= 50"]
        failureMessage = "{pokemon} exceeds the level 50 cap"
    }
}

Testing clauses

Build your format, add the clause, then try to queue with a team that should fail. The failure message will confirm whether your MoLang expression is catching the right cases.