FiftyOne Troubleshoot

Overview

Diagnose and fix common FiftyOne pain points. Match the user's symptom to the Issue Index, explain the root cause and proposed fix, get approval, then apply.

Shell commands in this skill are written for macOS/Linux. On Windows (non-WSL), adapt using PowerShell equivalents or use WSL.

Designed to grow: add new issues at the bottom as they are encountered.

Prerequisites

• FiftyOne installed: pip install fiftyone
• MCP server running (optional, for plugin-related fixes)

Key Directives

1. Always explain, propose, and confirm before acting

NEVER run a fix without first:

1. Explaining what is wrong and why
2. Describing what the fix will do
3. Asking the user to confirm: "Should I apply this fix?"

Wait for explicit user confirmation before executing anything that modifies files, config, or data.

2. Never touch user datasets — FiftyOne is the source of truth

• Except when given explicit and direct instructions by the user:
  • NEVER modify, edit, delete, or clone user datasets as part of troubleshooting
  • NEVER call fo.delete_dataset()
  • NEVER truncate, wipe, or alter dataset contents or sample fields to diagnose an issue
• Use FiftyOne's read-only API to inspect state: fo.list_datasets(), fo.load_dataset(), len(dataset), dataset.get_field_schema() — these are safe
• FiftyOne's state (datasets, fields, brain runs) is the ground truth; read it, never rewrite it to "fix" a problem

3. Never directly manipulate MongoDB

• NEVER use pymongo, db.drop_collection(), or raw MongoDB shell commands
• All data operations must go through the FiftyOne Python API

4. Never modify config or files silently

• NEVER change database_uri, database_name, or any config file without showing what will change and getting approval
• NEVER append to shell profiles (.zshrc, .bash_profile, virtualenv activate) without showing the exact line change and getting explicit user confirmation to apply

5. Restart processes after env / config changes

Any fix that sets an environment variable or modifies a config file only takes effect for new processes. Already-running App servers, service managers, and Python scripts will NOT pick up the change.

• After setting FIFTYONE_DATABASE_NAME or similar env vars, identify and restart any running FiftyOne processes
• Check with: ps aux | grep fiftyone
• Stop stale processes: pkill -f "fiftyone" (confirm with user first)

6. Always verify after fixing

Run the Health Check after every fix to confirm the environment is operational.

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Workflow

1. Diagnose — run the Diagnostic Quick-Check
2. Explain — describe the root cause in plain language
3. Propose — show the fix and what it will change
4. Confirm — ask the user: "Should I apply this?"
5. Execute — apply the fix only after approval
6. Verify — run the Health Check

---

Diagnostic Quick-Check

Handles connection failures gracefully — always produce useful output:

import sys

print(f"Python:  {sys.executable}")
print(f"Version: {sys.version.split()[0]}")

try:
    import fiftyone as fo
    print(f"FiftyOne: {fo.__version__}")
    print(f"Database: {fo.config.database_name}")
    print(f"DB URI:   {fo.config.database_uri or '(internal MongoDB)'}")
except ImportError:
    print("ERROR: fiftyone not installed — check Python environment, if needed run: pip install fiftyone")
    sys.exit(1)

try:
    print(f"Datasets: {fo.list_datasets()}")
    print("Connection: OK")
except Exception as e:
    print(f"Connection ERROR: {e}")
    print("→ Match this error to the Issue Index below")

---

Health Check

Run after any fix to confirm the environment is fully operational.

This script creates and destroys a temporary test dataset (_fo_health_check). It does not touch any user datasets. Do not manually create a dataset with the name "_fo_health_check".

import fiftyone as fo
import tempfile, os

TEST_NAME = "_fo_health_check"

try:
    # Clean up any debris from a previous failed check
    if TEST_NAME in fo.list_datasets():
        fo.delete_dataset(TEST_NAME)

    # Non-persistent: auto-removed if Python exits before cleanup
    dataset = fo.Dataset(TEST_NAME, persistent=False)
    dataset.add_sample(fo.Sample(
        filepath=os.path.join(tempfile.gettempdir(), "health_check.jpg")
    ))
    assert len(dataset) == 1, "Sample write failed"

    # Verify connection round-trip
    assert TEST_NAME in fo.list_datasets(), "Dataset not listed"

    print(f"OK — FiftyOne {fo.__version__} on database '{fo.config.database_name}'")

finally:
    # Always clean up, even on failure
    if TEST_NAME in fo.list_datasets():
        fo.delete_dataset(TEST_NAME)

---

Issue Index

Symptom	Section
Dataset disappeared after restart	Dataset Persistence
App won't open / not connected	App Connection
Changes not saved	Unsaved Changes
Video not playing / codec error	Video Codec
Too many open files (macOS)	Open Files Limit
App not loading in notebook / remote	Notebook / Remote
Plots not showing in notebook	Notebook Plots
MongoDB connection failure	MongoDB
Operator not found / plugin missing	Missing Plugin
"No executor available"	Delegated Operators
Dataset is read-only	Read-Only Dataset
Slow performance on large datasets	Performance
App showing stale / wrong data	Stale Data
Downgrading FiftyOne	Downgrading
Database version mismatch	DB Version Mismatch
Teams / OSS client type mismatch	Teams vs OSS

---

Issue: Dataset Disappeared

Cause: Datasets are non-persistent by default and are deleted when Python exits.

Fix:

import fiftyone as fo

# Make an existing dataset persistent
dataset = fo.load_dataset("my-dataset")
dataset.persistent = True

# Prevention: always create persistent datasets
dataset = fo.Dataset("my-dataset", persistent=True)

If the dataset is already gone from fo.list_datasets(), it cannot be recovered through FiftyOne — re-import from source files.

---

Issue: App Won't Open

Cause A — Script exits before the App loads. Fix: add session.wait().

session = fo.launch_app(dataset)
session.wait()  # keeps the process alive

Cause B — Windows multiprocessing. Fix: add the __main__ guard.

if __name__ == "__main__":
    session = fo.launch_app(dataset)
    session.wait()

Cause C — Port already in use.

session = fo.launch_app(dataset, port=<alternative-port>)  # e.g. 5152, 5153

Cause D — Stale process.

pkill -f "fiftyone"

---

Issue: Changes Not Saved

Fix — sample edits:

sample["my_field"] = "new_value"
sample.save()  # required

Fix — dataset-level properties:

dataset.info["description"] = "Updated"
dataset.save()  # required

Fix — bulk updates (no .save() needed):

dataset.set_values("my_field", [v1, v2, ...])

---

Issue: Video Codec

Cause: Video codec not supported by the browser's HTML5 player (requires MP4/H.264, WebM, or Ogg).

⚠️ Re-encoding overwrites files on disk. Show the user the exact paths that will be modified and get explicit confirmation before running.

import fiftyone.utils.video as fouv

# Re-encode all videos in a dataset
fouv.reencode_videos(fo.load_dataset("my-dataset"))

# Or a single file
fouv.reencode_video("/path/to/input.avi", "/path/to/output.mp4")

---

Issue: Too Many Open Files (macOS)

# Temporary (current session only)
ulimit -n 65536

# Permanent — add to your shell profile and reload it
# bash: ~/.bash_profile or ~/.bashrc
# zsh:  ~/.zshrc
echo "ulimit -n 65536" >> <your-shell-profile> && source <your-shell-profile>

---

Issue: App Not Loading in Notebook or Remote

Cause A — Remote Jupyter: localhost URL not reachable from browser.

fo.app_config.proxy_url = "http://your-server:<app-port>/proxy/<app-port>"
session = fo.launch_app(dataset)

Cause B — Google Colab / Databricks: works out of the box, no proxy needed.

Cause C — SSH remote: forward the port locally.

# Use the same port FiftyOne is listening on (default: 5151)
ssh -L <app-port>:localhost:<app-port> user@remote-server

---

Issue: Plots Not Appearing in Notebook

pip install plotly
jupyter labextension install jupyterlab-plotly

import plotly.offline as pyo
pyo.init_notebook_mode(connected=True)

---

Issue: MongoDB Connection Error

Symptoms: ConnectionFailure, ServerSelectionTimeoutError, hangs on import, port 27017 errors.

Diagnose:

ps aux | grep mongod     # is MongoDB running?
df -h                    # is disk full?

Fix A — Restart FiftyOne's MongoDB:

pkill -f "fiftyone.*mongod"   # kill stale process, then re-import fiftyone

Fix B — Free disk space. MongoDB will not start on a full disk.

Fix C — Use an external MongoDB instance (requires user confirmation):

// ~/.fiftyone/config.json
{ "database_uri": "mongodb://localhost:27017" }

Fix D — Reset internal MongoDB (last resort, destroys all datasets):

⚠️ Requires explicit user confirmation.

ls -la ~/.fiftyone/          # show what will be deleted
rm -rf ~/.fiftyone/var/      # only after user confirms

---

Issue: Operator Not Found

Diagnose:

fo.list_plugins()
# Via MCP:
list_plugins(enabled=True)
list_operators(builtin_only=False)

Fix:

fo.download_plugin("voxel51/fiftyone-plugins", plugin_names=["@voxel51/brain"])
fo.enable_plugin("@voxel51/brain")
# Via MCP:
download_plugin(url_or_repo="voxel51/fiftyone-plugins", plugin_names=["@voxel51/brain"])
enable_plugin(plugin_name="@voxel51/brain")

Operator prefix	Plugin
@voxel51/brain/*	@voxel51/brain
@voxel51/io/*	@voxel51/io
@voxel51/utils/*	@voxel51/utils
@voxel51/evaluation/*	@voxel51/evaluation
@voxel51/zoo/*	@voxel51/zoo

---

Issue: No Executor Available

Cause: Brain, evaluation, and annotation operators require the FiftyOne App running as executor.

launch_app()              # 1. launch app first
# wait 5-10 seconds
execute_operator(...)     # 2. then run the operator

---

Issue: Dataset is Read-Only

writable = fo.load_dataset("read-only-dataset").clone("my-writable-dataset")
writable.persistent = True

---

Issue: Slow Performance

# Use views, not full dataset iteration
view = dataset.match({"label": "cat"}).take(1000)

# Bulk updates over per-sample saves
dataset.set_values("my_score", values_list)   # fast
# vs: sample["my_score"] = v; sample.save()  # slow

# Add indexes for frequently filtered fields
dataset.create_index("ground_truth.detections.label")

---

Issue: Stale App Data

dataset.reload()
# or
session.dataset = fo.load_dataset("my-dataset")
session.refresh()

Browser: Cmd+Shift+R (macOS) / Ctrl+Shift+R (Windows/Linux).

---

Issue: Downgrading FiftyOne

pip install fiftyone==X.Y.Z
python -c "import fiftyone as fo; fo.migrate_database_if_necessary()"

⚠️ Export important datasets before downgrading.

---

Issue: Database Version Mismatch

Symptom:

OSError: You must have fiftyone>=X.Y.Z to migrate from vX.Y.Z to vA.B.C

Cause: All FiftyOne installs on a machine share the same MongoDB database (fiftyone by default). A newer version writes a forward-only version marker that older installs cannot read. Common when a dev virtualenv runs an older version than the system pip install.

Diagnose:

# Current env
python -c "import fiftyone as fo; print(fo.__version__, fo.config.database_name)"

# Check if the database is accessible at all
python -c "
import fiftyone as fo
try:
    print('datasets:', fo.list_datasets())
except Exception as e:
    print('inaccessible:', e)
"

# All Python installs on this machine
which -a python python3 | xargs -I{} sh -c '{} -c "import fiftyone as fo; print(\"{}: \", fo.__version__)" 2>/dev/null'

Fix A — Isolate the environment (recommended, no data loss):

Give the affected env its own database so it never conflicts with other installs.

# Find the virtualenv activate script
ACTIVATE=$(python -c "import sys; print(sys.prefix)")/bin/activate
echo $ACTIVATE   # confirm before editing

# Append isolation — pick a name that reflects your project
echo '
# Isolate FiftyOne database from other installations
export FIFTYONE_DATABASE_NAME=fiftyone-<your-project>' >> $ACTIVATE

source $ACTIVATE
python -c "import fiftyone as fo; print(fo.config.database_name)"

Then run the Health Check.

⚠️ After applying this fix, restart any running FiftyOne App or Python processes — env var changes only affect new processes. Check for stale processes: ps aux | grep fiftyone. Confirm with user before killing them.

Fix B — Per-session (no file changes):

FIFTYONE_DATABASE_NAME=fiftyone-<your-project> python your_script.py

Fix C — Upgrade to match the database version:

pip install "fiftyone>=X.Y.Z"

Fix D — Global config (affects all installs, confirm with user):

// ~/.fiftyone/config.json
{ "database_name": "fiftyone-<your-project>" }

---

Issue: FiftyOne Teams vs OSS Type Mismatch

Symptom:

ConnectionError: Cannot connect to database type 'fiftyone' with client type 'fiftyone-teams'

(or the inverse)

Cause: Teams and OSS clients use incompatible database types and cannot share a database.

Diagnose:

import fiftyone as fo
print(fo.__version__)
print(fo.config.database_name)
print(fo.config.database_uri or "(internal MongoDB)")
try:
    fo.list_datasets()
except Exception as e:
    print(e)

Fix — Isolate the OSS environment:

ACTIVATE=$(python -c "import sys; print(sys.prefix)")/bin/activate
echo $ACTIVATE   # confirm before editing
echo '
# Isolate FiftyOne database from Teams installation
export FIFTYONE_DATABASE_NAME=fiftyone-<your-project>' >> $ACTIVATE
source $ACTIVATE

Fix — Inspect Teams config if the error is unexpected:

cat ~/.fiftyone/config.json 2>/dev/null || echo "(no config)"
python -c "import fiftyone as fo; import json; print(json.dumps(fo.config.serialize(), indent=2))"

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Adding a New Issue

1. Add a row to the Issue Index
2. Add a ## Issue: <Name> section with: Symptom → Cause → Fix
3. Keep it self-contained — each section should be readable in isolation

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Resources

• FiftyOne FAQ
• FiftyOne Installation Guide
• FiftyOne Discord
• FiftyOne GitHub Issues