diff --git a/api/src/models/utils/filters.ts b/api/src/models/utils/filters.ts
index 63ac4252..7e468d81 100644
--- a/api/src/models/utils/filters.ts
+++ b/api/src/models/utils/filters.ts
@@ -1,4 +1,13 @@
-import { digit, float, int, noCharOf, type Parjser, string } from "parjs";
+import {
+	anyStringOf,
+	digit,
+	float,
+	int,
+	letter,
+	noCharOf,
+	type Parjser,
+	string,
+} from "parjs";
 import {
 	exactly,
 	many,
@@ -8,7 +17,11 @@ import {
 	stringify,
 	then,
 	thenq,
+	qthen,
+	later,
+	between,
 } from "parjs/combinators";
+import type { KError } from "../error";
 
 export type Filter = {
 	[key: string]: any;
@@ -19,12 +32,14 @@ type Value =
 	| { type: "int"; value: number }
 	| { type: "float"; value: number }
 	| { type: "date"; value: string }
-	| { type: "string"; value: string };
-type Operator = "eq" | "ne" | "gt" | "ge" | "lt" | "le" | "has" | "in";
-type Expression =
+	| { type: "string"; value: string }
+	| { type: "enum"; value: string };
+const operators = ["eq", "ne", "gt", "ge", "lt", "le", "has", "in"] as const;
+type Operator = (typeof operators)[number];
+export type Expression =
 	| { type: "op"; operator: Operator; property: Property; value: Value }
-	| { type: "and"; first: Expression; second: Expression }
-	| { type: "or"; first: Expression; second: Expression }
+	| { type: "and"; lhs: Expression; rhs: Expression }
+	| { type: "or"; lhs: Expression; rhs: Expression }
 	| { type: "not"; expression: Expression };
 
 function t<T>(parser: Parjser<T>): Parjser<T> {
@@ -32,6 +47,8 @@ function t<T>(parser: Parjser<T>): Parjser<T> {
 }
 
 const str = t(noCharOf(" ")).pipe(many1(), stringify()).expects("a string");
+const enumP = t(letter()).pipe(many1(), stringify()).expects("an enum value");
+
 const property = str.expects("a property");
 
 const intVal = t(int().pipe(map((i) => ({ type: "int" as const, value: i }))));
@@ -52,11 +69,52 @@ const dateVal = t(
 		})),
 	),
 );
-const strVal = t(str.pipe(map((s) => ({ type: "string" as const, value: s }))));
+const strVal = str.pipe(map((s) => ({ type: "string" as const, value: s })));
+const enumVal = enumP.pipe(map((e) => ({ type: "enum" as const, value: e })));
 const value = intVal
-	.pipe(or(floatVal, dateVal, strVal))
+	.pipe(or(floatVal, dateVal, strVal, enumVal))
 	.expects("a valid value");
 
-const operator = null;
+const operator = t(anyStringOf(...operators)).expects("an operator");
 
-export const parseFilter = (filter: string, config: Filter) => {};
+const operation = property
+	.pipe(
+		then(operator, value),
+		map(([property, operator, value]) => ({
+			type: "op" as const,
+			property,
+			operator,
+			value,
+		})),
+	)
+	.expects("an operation");
+
+export const expression = later<Expression>();
+
+const not = t(string("not")).pipe(
+	qthen(expression),
+	map((expression) => ({ type: "not" as const, expression })),
+);
+
+const andor = operation.pipe(
+	then(anyStringOf("and", "or").pipe(then(expression), many())),
+	map(([first, expr]) =>
+		expr.reduce<Expression>(
+			(lhs, [op, rhs]) => ({ type: op, lhs, rhs }),
+			first,
+		),
+	),
+);
+
+expression.init(
+	not.pipe(or(operation, expression.pipe(or(andor), between("(", ")")))),
+);
+
+export const parseFilter = (
+	filter: string,
+	config: Filter,
+): Expression | KError => {
+	const ret = expression.parse(filter);
+	if (ret.isOk) return ret.value;
+	return { status: 422, message: `Invalid filter: ${filter}.`, details: ret };
+};