diff --git a/tests/unit/test_repo_eligibility.py b/tests/unit/test_repo_eligibility.py
new file mode 100644
index 0000000..8bd7ed4
--- /dev/null
+++ b/tests/unit/test_repo_eligibility.py
@@ -0,0 +1,179 @@
+from __future__ import annotations
+
+import unittest
+from datetime import UTC, datetime
+
+from contribarena.config.schema import RepoCandidate
+from contribarena.tools.repo_eligibility import (
+    _is_external_recent_pr,
+    _looks_english,
+    _parse_github_datetime,
+    _prohibits_ai_or_bots,
+)
+
+
+class ParseGithubDatetimeTest(unittest.TestCase):
+    def test_empty_string_returns_none(self) -> None:
+        self.assertIsNone(_parse_github_datetime(""))
+
+    def test_iso_format_with_z_suffix(self) -> None:
+        result = _parse_github_datetime("2026-01-15T10:30:00Z")
+        self.assertIsNotNone(result)
+        self.assertEqual(2026, result.year)
+        self.assertEqual(1, result.month)
+        self.assertEqual(15, result.day)
+        self.assertEqual(10, result.hour)
+        self.assertEqual(30, result.minute)
+        self.assertEqual(0, result.second)
+        self.assertEqual(UTC, result.tzinfo)
+
+    def test_iso_format_with_timezone_offset(self) -> None:
+        result = _parse_github_datetime("2026-01-15T10:30:00+00:00")
+        self.assertIsNotNone(result)
+        self.assertEqual(2026, result.year)
+        self.assertEqual(UTC, result.tzinfo)
+
+    def test_invalid_format_returns_none(self) -> None:
+        self.assertIsNone(_parse_github_datetime("not-a-date"))
+        self.assertIsNone(_parse_github_datetime("2026/01/15"))
+
+    def test_timezone_conversion(self) -> None:
+        result = _parse_github_datetime("2026-01-15T10:30:00+05:00")
+        self.assertIsNotNone(result)
+        self.assertEqual(UTC, result.tzinfo)
+        self.assertEqual(5, result.hour)
+        self.assertEqual(30, result.minute)
+
+
+class LooksEnglishTest(unittest.TestCase):
+    def test_empty_string_returns_false(self) -> None:
+        self.assertFalse(_looks_english(""))
+
+    def test_whitespace_only_returns_false(self) -> None:
+        self.assertFalse(_looks_english("   \n\t  "))
+
+    def test_pure_ascii_returns_true(self) -> None:
+        text = "This is a simple English text with only ASCII characters."
+        self.assertTrue(_looks_english(text))
+
+    def test_high_ascii_ratio_returns_true(self) -> None:
+        text = "Hello world " * 10 + "é" * 10
+        self.assertTrue(_looks_english(text))
+
+    def test_low_ascii_ratio_returns_false(self) -> None:
+        text = "Привет мир " * 20
+        self.assertFalse(_looks_english(text))
+
+    def test_exactly_85_percent_boundary(self) -> None:
+        text = "a" * 85 + "é" * 15
+        self.assertFalse(_looks_english(text))
+
+    def test_above_85_percent_boundary(self) -> None:
+        text = "a" * 86 + "é" * 14
+        self.assertTrue(_looks_english(text))
+
+    def test_long_text_truncated_at_2000_chars(self) -> None:
+        text = "a" * 2000 + "é" * 1000
+        self.assertTrue(_looks_english(text))
+
+
+class ProhibitsAiOrBotsTest(unittest.TestCase):
+    def test_empty_text_returns_false(self) -> None:
+        self.assertFalse(_prohibits_ai_or_bots(""))
+
+    def test_no_prohibited_phrases_returns_false(self) -> None:
+        text = "We welcome contributions from everyone. Please read our guidelines."
+        self.assertFalse(_prohibits_ai_or_bots(text))
+
+    def test_no_ai_generated_detected(self) -> None:
+        text = "We do not accept no AI generated code in this repository."
+        self.assertTrue(_prohibits_ai_or_bots(text))
+
+    def test_ai_generated_contributions_not_accepted(self) -> None:
+        text = "AI-generated contributions are not accepted here."
+        self.assertTrue(_prohibits_ai_or_bots(text))
+
+    def test_do_not_submit_ai(self) -> None:
+        text = "Please do not submit AI written code."
+        self.assertTrue(_prohibits_ai_or_bots(text))
+
+    def test_no_bot_contributions(self) -> None:
+        text = "We have a policy of no bot contributions."
+        self.assertTrue(_prohibits_ai_or_bots(text))
+
+    def test_bot_contributions_not_accepted(self) -> None:
+        text = "Bot contributions are not accepted in this project."
+        self.assertTrue(_prohibits_ai_or_bots(text))
+
+    def test_automated_pull_requests_not_accepted(self) -> None:
+        text = "Automated pull requests are not accepted."
+        self.assertTrue(_prohibits_ai_or_bots(text))
+
+    def test_case_insensitive_detection(self) -> None:
+        text = "NO AI GENERATED CODE PLEASE"
+        self.assertTrue(_prohibits_ai_or_bots(text))
+
+    def test_partial_phrase_not_detected(self) -> None:
+        text = "We use AI tools but accept all contributions."
+        self.assertFalse(_prohibits_ai_or_bots(text))
+
+
+class IsExternalRecentPrTest(unittest.TestCase):
+    def setUp(self) -> None:
+        self.candidate = RepoCandidate(
+            owner="testowner", repo="testrepo", url="https://github.com/testowner/testrepo"
+        )
+        self.since = datetime(2026, 1, 1, tzinfo=UTC)
+
+    def test_empty_merged_at_returns_false(self) -> None:
+        item = {"mergedAt": "", "author": {"login": "contributor"}}
+        self.assertFalse(_is_external_recent_pr(item, self.candidate, self.since))
+
+    def test_missing_author_returns_false(self) -> None:
+        item = {"mergedAt": "2026-06-15T10:00:00Z"}
+        self.assertFalse(_is_external_recent_pr(item, self.candidate, self.since))
+
+    def test_missing_login_returns_false(self) -> None:
+        item = {"mergedAt": "2026-06-15T10:00:00Z", "author": {}}
+        self.assertFalse(_is_external_recent_pr(item, self.candidate, self.since))
+
+    def test_old_pr_returns_false(self) -> None:
+        item = {"mergedAt": "2025-06-15T10:00:00Z", "author": {"login": "contributor"}}
+        self.assertFalse(_is_external_recent_pr(item, self.candidate, self.since))
+
+    def test_recent_external_pr_returns_true(self) -> None:
+        item = {"mergedAt": "2026-06-15T10:00:00Z", "author": {"login": "contributor"}}
+        self.assertTrue(_is_external_recent_pr(item, self.candidate, self.since))
+
+    def test_owner_pr_returns_false(self) -> None:
+        item = {"mergedAt": "2026-06-15T10:00:00Z", "author": {"login": "testowner"}}
+        self.assertFalse(_is_external_recent_pr(item, self.candidate, self.since))
+
+    def test_owner_pr_case_insensitive(self) -> None:
+        item = {"mergedAt": "2026-06-15T10:00:00Z", "author": {"login": "TestOwner"}}
+        self.assertFalse(_is_external_recent_pr(item, self.candidate, self.since))
+
+    def test_bot_pr_returns_false(self) -> None:
+        item = {"mergedAt": "2026-06-15T10:00:00Z", "author": {"login": "dependabot[bot]"}}
+        self.assertFalse(_is_external_recent_pr(item, self.candidate, self.since))
+
+    def test_rest_api_format_merged_at(self) -> None:
+        item = {"merged_at": "2026-06-15T10:00:00Z", "user": {"login": "contributor"}}
+        self.assertTrue(_is_external_recent_pr(item, self.candidate, self.since))
+
+    def test_rest_api_format_user_field(self) -> None:
+        item = {"merged_at": "2026-06-15T10:00:00Z", "user": {"login": "contributor"}}
+        self.assertTrue(_is_external_recent_pr(item, self.candidate, self.since))
+
+    def test_author_not_dict_treated_as_missing(self) -> None:
+        item = {"mergedAt": "2026-06-15T10:00:00Z", "author": "not-a-dict"}
+        self.assertFalse(_is_external_recent_pr(item, self.candidate, self.since))
+
+    def test_exactly_at_since_boundary(self) -> None:
+        item = {"mergedAt": "2026-01-01T00:00:00Z", "author": {"login": "contributor"}}
+        # Equal timestamps are considered recent (merged_at >= since)
+        self.assertTrue(_is_external_recent_pr(item, self.candidate, self.since))
+
+    def test_one_second_after_since(self) -> None:
+        item = {"mergedAt": "2026-01-01T00:00:01Z", "author": {"login": "contributor"}}
+        self.assertTrue(_is_external_recent_pr(item, self.candidate, self.since))