diff --git a/src/isolate/backends/_base.py b/src/isolate/backends/_base.py
index d907e006..ecfde403 100644
--- a/src/isolate/backends/_base.py
+++ b/src/isolate/backends/_base.py
@@ -97,7 +97,13 @@ def log(
         source: LogSource = LogSource.BUILDER,
     ) -> None:
         """Log a message."""
-        log_msg = Log(message, level=level, source=source, bound_env=self)
+        log_msg = Log(
+            message,
+            level=level,
+            source=source,
+            bound_env=self,
+            is_json=self.settings.json_logs,
+        )
         self.settings.log(log_msg)
 
 
diff --git a/src/isolate/backends/settings.py b/src/isolate/backends/settings.py
index 2dee7394..0d435d9c 100644
--- a/src/isolate/backends/settings.py
+++ b/src/isolate/backends/settings.py
@@ -18,6 +18,7 @@
 
 _SYSTEM_TEMP_DIR = Path(tempfile.gettempdir())
 _STRICT_CACHE = os.getenv("ISOLATE_STRICT_CACHE", "0") == "1"
+JSON_LOGS = os.getenv("ISOLATE_JSON_LOGS", "0") == "1"
 
 
 @dataclass(frozen=True)
@@ -26,6 +27,7 @@ class IsolateSettings:
     serialization_method: str = "pickle"
     log_hook: Callable[[Log], None] = print
     strict_cache: bool = _STRICT_CACHE
+    json_logs: bool = JSON_LOGS
 
     def log(self, log: Log) -> None:
         self.log_hook(self._infer_log_level(log))
@@ -39,7 +41,7 @@ def _infer_log_level(self, log: Log) -> Log:
         if log.source in (LogSource.BUILDER, LogSource.BRIDGE):
             return replace(log, level=LogLevel.TRACE)
 
-        line = log.message.lower()
+        line = log.message_str().lower()
 
         if line.startswith("error") or "[error]" in line:
             return replace(log, level=LogLevel.ERROR)
diff --git a/src/isolate/connections/_local/_base.py b/src/isolate/connections/_local/_base.py
index 76f87a5a..2a8f387f 100644
--- a/src/isolate/connections/_local/_base.py
+++ b/src/isolate/connections/_local/_base.py
@@ -18,6 +18,7 @@
 
 from isolate import __version__ as isolate_version
 from isolate.backends.common import active_python, get_executable_path, logged_io
+from isolate.backends.settings import JSON_LOGS
 from isolate.connections.common import AGENT_SIGNATURE
 from isolate.logs import LogLevel, LogSource
 
@@ -102,6 +103,7 @@ class PythonExecutionBase(Generic[ConnectionType]):
     environment: BaseEnvironment
     environment_path: Path
     extra_inheritance_paths: list[Path] = field(default_factory=list)
+    json_logs: bool = True
 
     @contextmanager
     def start_process(
@@ -147,7 +149,7 @@ def start_process(
             ),
         ) as (stdout, stderr, log_fd):
             yield subprocess.Popen(
-                self.get_python_cmd(python_executable, connection, log_fd),
+                self.get_python_cmd(python_executable, connection, log_fd, JSON_LOGS),
                 env=env,
                 stdout=stdout,
                 stderr=stderr,
@@ -191,6 +193,7 @@ def get_python_cmd(
         executable: Path,
         connection: ConnectionType,
         log_fd: int,
+        json_logs: bool = False,
     ) -> list[str | Path]:
         """Return the command to run the agent process with."""
         raise NotImplementedError
diff --git a/src/isolate/connections/grpc/_base.py b/src/isolate/connections/grpc/_base.py
index 2b22e259..b258de04 100644
--- a/src/isolate/connections/grpc/_base.py
+++ b/src/isolate/connections/grpc/_base.py
@@ -165,6 +165,7 @@ def get_python_cmd(
         executable: Path,
         connection: str,
         log_fd: int,
+        json_logs: bool = False,
     ) -> List[Union[str, Path]]:
         return [
             executable,
@@ -173,6 +174,7 @@ def get_python_cmd(
             connection,
             "--log-fd",
             str(log_fd),
+            *(["--json-logs"] if json_logs else []),
         ]
 
     def handle_agent_log(
diff --git a/src/isolate/connections/grpc/agent.py b/src/isolate/connections/grpc/agent.py
index 03d9acc6..18ddb3f0 100644
--- a/src/isolate/connections/grpc/agent.py
+++ b/src/isolate/connections/grpc/agent.py
@@ -11,9 +11,12 @@
 from __future__ import annotations
 
 import asyncio
+import contextvars
+import json
 import os
 import signal
 import sys
+import threading
 import traceback
 from argparse import ArgumentParser
 from concurrent import futures
@@ -22,6 +25,7 @@
     Any,
     AsyncIterator,
     Iterable,
+    TextIO,
 )
 
 from grpc import StatusCode, aio, local_server_credentials
@@ -41,6 +45,106 @@
 
 IDLE_TIMEOUT_SECONDS = int(os.getenv("ISOLATE_AGENT_IDLE_TIMEOUT_SECONDS", "0"))
 
+isolate_log_context: contextvars.ContextVar[dict[str, Any]] = contextvars.ContextVar(
+    "ISOLATE_CONTEXT_VAR_LOG", default={}
+)
+
+
+def get_log_context() -> dict[str, Any]:
+    """Extract the contextvar that is set to the log_context."""
+    value = isolate_log_context.get()
+    if not isinstance(value, dict):
+        return {}
+
+    return value
+
+
+class JsonStdoutProxy:
+    """
+    A proxy around a real text stream (usually sys.__stdout__).
+    - Intercepts write/writelines and emits JSON lines with contextvars
+    - Delegates everything else to the wrapped stream to preserve compatibility.
+    - Avoids recursion by always writing to the underlying stream.
+    """
+
+    def __init__(self, underlying):
+        self._u = underlying
+        self._local = threading.local()
+
+    def write(self, s: str) -> int:
+        # Many libs call write(""); keep semantics cheap.
+        if not s:
+            return 0
+
+        # Prevent re-entrancy if something in encoding/IO calls back into sys.stdout.
+        if getattr(self._local, "in_write", False):
+            return self._u.write(s)
+
+        self._local.in_write = True
+        try:
+            # Preserve "print" behavior: print() typically writes text
+            # possibly with '\n'
+            # Emit one JSON object per line. Keep partial lines buffered per-thread.
+            buf = getattr(self._local, "buf", "")
+            buf += s
+            lines = buf.splitlines(keepends=True)
+
+            out_count = 0
+            new_buf = ""
+
+            for chunk in lines:
+                if chunk.endswith("\n") or chunk.endswith("\r\n"):
+                    msg = chunk.rstrip("\r\n")
+                    payload = self._format_record(msg)
+                    out_count += self._u.write(payload + "\n")
+                else:
+                    # Incomplete line: keep buffering
+                    new_buf += chunk
+
+            self._local.buf = new_buf
+            return len(s)
+        finally:
+            self._local.in_write = False
+
+    def flush(self) -> None:
+        # Flush any buffered partial line as a final record (optional choice).
+        if getattr(self._local, "in_write", False):
+            return self._u.flush()
+
+        buf = getattr(self._local, "buf", "")
+        if buf:
+            self._local.buf = ""
+            payload = self._format_record(buf)
+            self._u.write(payload + "\n")
+        self._u.flush()
+
+    def writelines(self, lines: list[str]) -> None:
+        for line in lines:
+            self.write(line)
+
+    def _format_record(self, message: str) -> str:
+        record = {
+            "line": message,
+        }
+        # Add the log context to the json so we propagate contextvars
+        record.update(get_log_context())
+        return json.dumps(record, ensure_ascii=False)
+
+    def __getattr__(self, name: str) -> Any:
+        # Delegate missing attrs/methods to underlying stream
+        # (isatty, fileno, encoding, etc.)
+        return getattr(self._u, name)
+
+    def __iter__(self):
+        return iter(self._u)
+
+    def __enter__(self):
+        self._u.__enter__()
+        return self
+
+    def __exit__(self, exc_type, exc, tb):
+        return self._u.__exit__(exc_type, exc, tb)
+
 
 @dataclass
 class AbortException(Exception):
@@ -48,11 +152,11 @@ class AbortException(Exception):
 
 
 class AgentServicer(definitions.AgentServicer):
-    def __init__(self, log_fd: int | None = None):
+    def __init__(self, log_file: TextIO | None = None):
         super().__init__()
 
         self._run_cache: dict[str, Any] = {}
-        self._log = sys.stdout if log_fd is None else os.fdopen(log_fd, "w")
+        self._log = log_file if log_file is not None else sys.stdout
         self._thread_pool = futures.ThreadPoolExecutor(max_workers=1)
         self._idle_timeout_seconds = IDLE_TIMEOUT_SECONDS
         self._is_running = asyncio.Event()
@@ -305,10 +409,24 @@ def create_server(address: str) -> aio.Server:
     return server
 
 
-async def run_agent(address: str, log_fd: int | None = None) -> int:
+async def run_agent(
+    address: str, log_fd: int | None = None, json_logs: bool = False
+) -> int:
     """Run the agent servicer on the given address."""
+    # Determine the base log file
+    if log_fd is None:
+        log_file: TextIO = sys.stdout
+    else:
+        log_file = os.fdopen(log_fd, "w")
+
+    # Apply JSON wrapper if requested
+    if json_logs:
+        sys.stdout = JsonStdoutProxy(sys.__stdout__)  # type: ignore[assignment]
+        sys.stderr = JsonStdoutProxy(sys.__stderr__)  # type: ignore[assignment]
+        log_file = JsonStdoutProxy(log_file)  # type: ignore[assignment]
+
     server = create_server(address)
-    servicer = AgentServicer(log_fd=log_fd)
+    servicer = AgentServicer(log_file=log_file)
 
     # This function just calls some methods on the server
     # and register a generic handler for the bridge. It does
@@ -335,9 +453,12 @@ async def main() -> int:
     parser = ArgumentParser()
     parser.add_argument("address", type=str)
     parser.add_argument("--log-fd", type=int)
+    parser.add_argument("--json-logs", action="store_true", default=False)
 
     options = parser.parse_args()
-    return await run_agent(options.address, log_fd=options.log_fd)
+    return await run_agent(
+        options.address, log_fd=options.log_fd, json_logs=options.json_logs
+    )
 
 
 if __name__ == "__main__":
diff --git a/src/isolate/connections/grpc/interface.py b/src/isolate/connections/grpc/interface.py
index 4e1d2829..4f9d948e 100644
--- a/src/isolate/connections/grpc/interface.py
+++ b/src/isolate/connections/grpc/interface.py
@@ -49,7 +49,7 @@ def _(message: definitions.Log) -> Log:
 @to_grpc.register
 def _(obj: Log) -> definitions.Log:
     return definitions.Log(
-        message=obj.message,
+        message=obj.message_str(),
         source=definitions.LogSource.Value(obj.source.name.upper()),
         level=definitions.LogLevel.Value(obj.level.name.upper()),
         timestamp=timestamp.from_datetime(obj.timestamp),
diff --git a/src/isolate/connections/ipc/_base.py b/src/isolate/connections/ipc/_base.py
index 2301d0f4..59175a8f 100644
--- a/src/isolate/connections/ipc/_base.py
+++ b/src/isolate/connections/ipc/_base.py
@@ -203,6 +203,7 @@ def get_python_cmd(
         executable: Path,
         connection: AgentListener,
         log_fd: int,
+        json_logs: bool = False,
     ) -> list[str | Path]:
         assert isinstance(connection.address, tuple)
         return [
@@ -217,6 +218,7 @@ def get_python_cmd(
             self.environment.settings.serialization_method,
             "--log-fd",
             str(log_fd),
+            *(["--json-logs"] if json_logs else []),
         ]
 
     def handle_agent_log(
diff --git a/src/isolate/logger.py b/src/isolate/logger.py
index 9727b0b9..51e7f217 100644
--- a/src/isolate/logger.py
+++ b/src/isolate/logger.py
@@ -15,7 +15,13 @@ class IsolateLogger:
     def __init__(self, log_labels: Dict[str, str]):
         self.log_labels = log_labels
 
-    def log(self, level: LogLevel, message: str, source: LogSource) -> None:
+    def log(
+        self,
+        level: LogLevel,
+        message: str,
+        source: LogSource,
+        line_labels: Dict[str, str],
+    ) -> None:
         record = {
             # Set the timestamp from source so we can be sure no buffering or
             # latency is affecting the timestamp.
@@ -25,6 +31,7 @@ def log(self, level: LogLevel, message: str, source: LogSource) -> None:
             "message": message,
             **self.log_labels,
             **self.extra_labels,
+            **line_labels,
         }
         print(json.dumps(record))
 
diff --git a/src/isolate/logs.py b/src/isolate/logs.py
index e70de110..ddd5f194 100644
--- a/src/isolate/logs.py
+++ b/src/isolate/logs.py
@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+import json
 import tempfile
 from dataclasses import dataclass, field
 from datetime import datetime, timezone
@@ -63,6 +64,8 @@ class Log:
     level: LogLevel = LogLevel.INFO
     bound_env: BaseEnvironment | None = field(default=None, repr=False)
     timestamp: datetime = field(default_factory=lambda: datetime.now(timezone.utc))
+    is_json: bool = field(default=False)
+    _parsed_message: dict | None = field(default=None, init=False, repr=False)
 
     def __str__(self) -> str:
         parts = [self.timestamp.strftime("%m/%d/%Y %H:%M:%S")]
@@ -74,3 +77,26 @@ def __str__(self) -> str:
         parts.append(f"[{self.source}]".ljust(10))
         parts.append(f"[{self.level}]".ljust(10))
         return " ".join(parts) + self.message
+
+    def message_str(self) -> str:
+        parsed = self.from_json()
+        return parsed["line"] if "line" in parsed else self.message
+
+    def message_meta(self) -> dict:
+        parsed = self.from_json()
+        if "line" in parsed:
+            # The metadata is everything except the actual log line.
+            return {k: v for k, v in parsed.items() if k != "line"}
+        return parsed
+
+    def from_json(self) -> dict[str, str]:
+        if not self.is_json:
+            return {}
+        if self._parsed_message is not None:
+            return self._parsed_message
+        try:
+            self._parsed_message = json.loads(self.message)
+            return self._parsed_message
+        except json.JSONDecodeError:
+            self._parsed_message = {}
+            return self._parsed_message
diff --git a/src/isolate/server/server.py b/src/isolate/server/server.py
index f659e913..e2a81c85 100644
--- a/src/isolate/server/server.py
+++ b/src/isolate/server/server.py
@@ -541,8 +541,13 @@ class LogHandler:
     task: RunTask
 
     def handle(self, log: Log) -> None:
-        if not SKIP_EMPTY_LOGS or log.message.strip():
-            self.task.logger.log(log.level, log.message, source=log.source)
+        if not SKIP_EMPTY_LOGS or log.message_str().strip():
+            self.task.logger.log(
+                log.level,
+                log.message_str(),
+                source=log.source,
+                line_labels=log.message_meta(),
+            )
             self._add_log_to_queue(log)
 
     def _add_log_to_queue(self, log: Log) -> None:
diff --git a/tests/test_log.py b/tests/test_log.py
index fc08d11e..09cbc844 100644
--- a/tests/test_log.py
+++ b/tests/test_log.py
@@ -33,3 +33,44 @@ def test_log_definition_conversion():
     message = definitions.Log(message="message", source=0, level=3)
     level_definition = definitions.LogLevel.Name(message.level)
     assert LogLevel[level_definition.upper()] == LogLevel.WARNING
+
+
+def test_json_logs():
+    log = Log(
+        message='{"line": "This is a log line", "user_id": 123, "task": "test"}',
+        source=LogSource.USER,
+        level=LogLevel.INFO,
+        is_json=True,
+    )
+    assert log.message_str() == "This is a log line"
+    meta = log.message_meta()
+    assert meta["user_id"] == 123
+    assert meta["task"] == "test"
+    assert "line" not in meta
+
+    # Ensure metatada didn't modify the original message
+    assert log.message_str() == "This is a log line"
+
+    non_json_log = Log(
+        message="This is a plain log line",
+        source=LogSource.USER,
+        level=LogLevel.INFO,
+        is_json=False,
+    )
+    assert non_json_log.message_str() == "This is a plain log line"
+    meta = non_json_log.message_meta()
+    assert meta == {}
+
+    malformed_json_log = Log(
+        # Missing closing brace
+        message='{"line": "This is a line", "user_id": 123, "task": "test"',
+        source=LogSource.USER,
+        level=LogLevel.INFO,
+        is_json=True,
+    )
+    assert (
+        malformed_json_log.message_str()
+        == '{"line": "This is a line", "user_id": 123, "task": "test"'
+    )
+    meta = malformed_json_log.message_meta()
+    assert meta == {}