diff --git a/read_tools.py b/read_tools.py
index 36230ac..b09c08d 100644
--- a/read_tools.py
+++ b/read_tools.py
@@ -241,7 +241,15 @@ async def github_read_file(repo: str, path: str, ref: str = "") -> str:
         """
         if err := bad_repo(repo):
             return err
-        return "Error: github_read_file is not implemented yet (stub — to be built by the team)."
+        args = ["api", f"repos/{repo}/contents/{path}", "-H", "Accept: application/vnd.github.raw+json"]
+        if ref.strip():
+            args += ["-f", f"ref={ref}"]
+        rc, out, serr = await run_gh(args)
+        if gh_err := check_gh_error(rc, serr):
+            return gh_err
+        if len(out) > 20000:
+            out = out[:20000] + "\n… (truncated at 20000 chars)"
+        return out
 
     @tool
     async def github_repo_contents(repo: str, path: str = "", ref: str = "") -> str:
diff --git a/tests/test_read_tools.py b/tests/test_read_tools.py
new file mode 100644
index 0000000..a88aabd
--- /dev/null
+++ b/tests/test_read_tools.py
@@ -0,0 +1,68 @@
+"""github_read_file over a mocked `gh` — formats raw content, errors readably, caps size.
+
+Host-free: we mock ``ghplugin.read_tools.run_gh`` (the name bound in read_tools) so no
+real `gh`/network is touched. The tool is a langchain ``@tool``; invoke via ``ainvoke``.
+"""
+
+from __future__ import annotations
+
+from unittest.mock import AsyncMock, patch
+
+import pytest
+from ghplugin.read_tools import get_read_tools
+
+
+def _read_file_tool():
+    for t in get_read_tools():
+        if t.name == "github_read_file":
+            return t
+    raise AssertionError("github_read_file tool not found")
+
+
+@pytest.mark.asyncio
+async def test_success_returns_raw_content():
+    with patch("ghplugin.read_tools.run_gh", new=AsyncMock(return_value=(0, "file content", ""))):
+        result = await _read_file_tool().ainvoke({"repo": "owner/name", "path": "README.md"})
+    assert result == "file content"
+
+
+@pytest.mark.asyncio
+async def test_ref_is_passed_to_gh_args():
+    mock = AsyncMock(return_value=(0, "ok", ""))
+    with patch("ghplugin.read_tools.run_gh", mock):
+        await _read_file_tool().ainvoke({"repo": "owner/name", "path": "docs/guide.md", "ref": "main"})
+    args = mock.call_args.args[0]
+    assert "-f" in args
+    assert "ref=main" in args
+
+
+@pytest.mark.asyncio
+async def test_invalid_repo_returns_bad_repo_error():
+    # run_gh must NOT be called for an invalid repo.
+    mock = AsyncMock(return_value=(0, "nope", ""))
+    with patch("ghplugin.read_tools.run_gh", mock):
+        result = await _read_file_tool().ainvoke({"repo": "bad", "path": "README.md"})
+    assert result.startswith("Error: 'repo' must be")
+    mock.assert_not_called()
+
+
+@pytest.mark.asyncio
+async def test_gh_error_is_surfaced():
+    with patch("ghplugin.read_tools.run_gh", new=AsyncMock(return_value=(1, "", "not found"))):
+        result = await _read_file_tool().ainvoke({"repo": "owner/name", "path": "missing.md"})
+    assert result.startswith("Error (gh exit 1)")
+
+
+@pytest.mark.asyncio
+async def test_long_content_is_truncated():
+    with patch("ghplugin.read_tools.run_gh", new=AsyncMock(return_value=(0, "x" * 25000, ""))):
+        result = await _read_file_tool().ainvoke({"repo": "owner/name", "path": "big.txt"})
+    assert result.endswith("… (truncated at 20000 chars)")
+    assert len(result) == 20000 + len("\n… (truncated at 20000 chars)")
+
+
+@pytest.mark.asyncio
+async def test_empty_content_returns_empty_string():
+    with patch("ghplugin.read_tools.run_gh", new=AsyncMock(return_value=(0, "", ""))):
+        result = await _read_file_tool().ainvoke({"repo": "owner/name", "path": "empty.txt"})
+    assert result == ""