diff --git a/src/lib/providers/vercel/__tests__/translator.test.ts b/src/lib/providers/vercel/__tests__/translator.test.ts
index a69e214..91ede49 100644
--- a/src/lib/providers/vercel/__tests__/translator.test.ts
+++ b/src/lib/providers/vercel/__tests__/translator.test.ts
@@ -274,6 +274,89 @@ describe('vercel/translator', () => {
       }
     })
 
+    // Regression tests for #261: `ne`/`not_contains`/`not_in` previously fell
+    // through mapUnifiedOperatorToVercel's `mapping[op] || 'eq'` fallback
+    // with no warning — silently inverting a rule's intent (e.g. "method is
+    // not POST" became "method is POST"). Vercel has no dedicated negative
+    // operators for these, only a positive operator + `neg` flag (same
+    // mechanism `not_exists` already uses via `nex`), so the fix maps each
+    // to its positive Vercel operator with `neg: true` forced on.
+    it('maps ne/not_contains/not_in to their positive Vercel operator with neg forced true', () => {
+      const ops = [
+        { unified: 'ne', vercel: 'eq' },
+        { unified: 'not_contains', vercel: 'sub' },
+        { unified: 'not_in', vercel: 'inc' },
+      ] as const
+
+      for (const { unified, vercel } of ops) {
+        const rule = makeUnifiedRule({
+          conditions: [{ field: 'path', operator: unified, value: 'test' }],
+        })
+        const { result } = unifiedToVercel(rule)
+        const condition = result.conditionGroup[0]!.conditions[0]!
+        expect(condition.op).toBe(vercel)
+        expect(condition.neg).toBe(true)
+      }
+    })
+
+    it('composes a negated ne condition (double negation) back to a plain, non-negated eq', () => {
+      // `ne` already means "not equal"; `negated: true` on top of that means
+      // "NOT (not equal)" = "equal" — the two negations must cancel (XOR),
+      // not stack into a nonsensical `neg: true` re-affirmation.
+      const rule = makeUnifiedRule({
+        conditions: [{ field: 'path', operator: 'ne', value: 'test', negated: true }],
+      })
+      const { result } = unifiedToVercel(rule)
+      const condition = result.conditionGroup[0]!.conditions[0]!
+      expect(condition.op).toBe('eq')
+      expect(condition.neg).toBe(false)
+    })
+
+    it('still honors negated on an already-working operator exactly as before (eq + negated -> neg: true)', () => {
+      const rule = makeUnifiedRule({
+        conditions: [{ field: 'path', operator: 'eq', value: 'test', negated: true }],
+      })
+      const { result } = unifiedToVercel(rule)
+      const condition = result.conditionGroup[0]!.conditions[0]!
+      expect(condition.op).toBe('eq')
+      expect(condition.neg).toBe(true)
+    })
+
+    // Regression tests for #261: gt/ge/lt/le have no Vercel equivalent at
+    // all (Vercel's operator vocabulary has no numeric-comparison concept),
+    // so — unlike ne/not_contains/not_in above — there's no positive-operator
+    // fallback to map to. The condition must be dropped with a critical
+    // warning, not silently mis-mapped to eq.
+    it('drops a numeric-comparison condition (gt/ge/lt/le) and warns instead of defaulting to eq', () => {
+      const numericOps = ['gt', 'ge', 'lt', 'le'] as const
+
+      for (const op of numericOps) {
+        // `asn` (-> Vercel's geo_as_number) has a real Vercel field mapping,
+        // unlike Cloudflare-only fields like `port` — this must fail on the
+        // *operator*, not get dropped earlier for having no Vercel field at
+        // all (which would happen for `port` and not exercise this path).
+        const rule = makeUnifiedRule({
+          conditions: [
+            { field: 'asn', operator: op, value: 13335 },
+            { field: 'path', operator: 'eq', value: '/api' },
+          ],
+        })
+        const { result, warnings } = unifiedToVercel(rule)
+
+        expect(result.conditionGroup[0]!.conditions).toHaveLength(1)
+        expect(result.conditionGroup[0]!.conditions[0]!.type).toBe('path')
+        expect(warnings.some((w) => w.severity === 'critical' && w.message.includes(op))).toBe(true)
+      }
+    })
+
+    it('throws when the only condition on the rule uses an unsupported operator', () => {
+      const rule = makeUnifiedRule({
+        conditions: [{ field: 'path', operator: 'gt', value: 1024 }],
+      })
+
+      expect(() => unifiedToVercel(rule)).toThrow(/no conditions Vercel can represent/)
+    })
+
     it('translates unified field types back to Vercel types', () => {
       const mappings = [
         { unified: 'host', vercel: 'host' },
diff --git a/src/lib/providers/vercel/translator.ts b/src/lib/providers/vercel/translator.ts
index 347b1a7..5a6c58e 100644
--- a/src/lib/providers/vercel/translator.ts
+++ b/src/lib/providers/vercel/translator.ts
@@ -258,9 +258,28 @@ function buildVercelConditionGroups(
         )
         continue
       }
+      const mappedOperator = mapUnifiedOperatorToVercel(condition.operator)
+      if (!mappedOperator) {
+        warnings.push(
+          TranslationWarningSystem.createUnsupportedFeatureWarning(
+            `operator '${condition.operator}'`,
+            'unified config',
+            'Vercel',
+            ruleId,
+            condition.field,
+          ),
+        )
+        continue
+      }
       mapped.push({
-        op: mapUnifiedOperatorToVercel(condition.operator),
-        neg: condition.negated,
+        op: mappedOperator.op,
+        // XOR the operator's own required negation (e.g. `ne` -> `eq` +
+        // forced neg) with the condition's independent `negated` flag —
+        // `forceNeg: false` for every operator that doesn't need one makes
+        // this reduce to plain `condition.negated`, so this is a strict
+        // superset of the previous `neg: condition.negated` behavior, not a
+        // change for any operator already working correctly.
+        neg: mappedOperator.forceNeg !== Boolean(condition.negated),
         type,
         key: condition.key,
         value: condition.value,
@@ -289,19 +308,43 @@ function mapVercelOperatorToUnified(op: string): Operator {
   return mapping[op] || 'eq'
 }
 
-function mapUnifiedOperatorToVercel(op: string): VercelRuleOperator {
-  const mapping: Record<string, VercelRuleOperator> = {
-    eq: 'eq',
-    starts_with: 'pre',
-    ends_with: 'suf',
-    in: 'inc',
-    contains: 'sub',
-    matches: 're',
-    exists: 'ex',
-    not_exists: 'nex',
+/**
+ * Maps a unified operator to its Vercel equivalent, or `null` if Vercel has
+ * no representation for it at all. Previously this defaulted any unmapped
+ * operator to plain `eq` with no warning — silently changing what a rule
+ * matches, sometimes inverting it outright (`ne` "is not X" became `eq` "is
+ * X"). See #261.
+ *
+ * Returns `{ op, forceNeg }` rather than just `op`: Vercel has no dedicated
+ * "not equal"/"does not contain"/"is not any of" operators, only positive
+ * ones plus a `neg` flag (`VercelRuleOperator` in types/vercel.ts documents
+ * the negative form each positive operator has via `neg`, except `ex`/`nex`,
+ * which are already their own negated pair). `ne`/`not_contains`/`not_in`
+ * are fully representable this way — `forceNeg: true` — but the caller must
+ * compose that with the condition's own independent `negated` flag (XOR),
+ * not just overwrite it with one or the other.
+ *
+ * `gt`/`ge`/`lt`/`le` have no entry and return `null`: Vercel's operator
+ * vocabulary (`eq, pre, suf, inc, sub, re, ex, nex`) has no numeric
+ * comparison concept at all, so there's nothing to fall back to — the caller
+ * must drop the condition and warn rather than silently mis-map it to `eq`.
+ */
+function mapUnifiedOperatorToVercel(op: Operator): { op: VercelRuleOperator; forceNeg: boolean } | null {
+  const mapping: Partial<Record<Operator, { op: VercelRuleOperator; forceNeg: boolean }>> = {
+    eq: { op: 'eq', forceNeg: false },
+    ne: { op: 'eq', forceNeg: true },
+    starts_with: { op: 'pre', forceNeg: false },
+    ends_with: { op: 'suf', forceNeg: false },
+    in: { op: 'inc', forceNeg: false },
+    not_in: { op: 'inc', forceNeg: true },
+    contains: { op: 'sub', forceNeg: false },
+    not_contains: { op: 'sub', forceNeg: true },
+    matches: { op: 're', forceNeg: false },
+    exists: { op: 'ex', forceNeg: false },
+    not_exists: { op: 'nex', forceNeg: false },
   }
 
-  return mapping[op] || 'eq'
+  return mapping[op] ?? null
 }
 
 /**