Protocol Verification

Do not use uv run for one-off simulate/analyze calls. It checks and potentially rebuilds the venv on every invocation, adding significant latency. Call the venv binaries directly.

Working Directories

All local dev artifacts are gitignored and live at the monorepo root:

Simulation

Produces a human-readable runlog of every command the robot would execute. Use for quick validation.

⛔ RTP protocols cannot be simulated. opentrons_simulate has no --rtp-values or --rtp-files flag. If the protocol defines add_parameters() (any RTP — including CSV, int, bool, str, or float), you must tell the user this upfront and use opentrons analyze instead. Do not attempt to simulate an RTP protocol and let it fail; explain the limitation first, then switch to analyze automatically.

# Standard
api/.venv/bin/opentrons_simulate tmp-protocols/my_protocol.py

# With custom labware (can be specified multiple times)
api/.venv/bin/opentrons_simulate tmp-protocols/my_protocol.py \
    -L tmp-custom-labware/

The current working directory is always searched for custom labware implicitly.

Simulation Options

Interpreting Results

• Success: runlog prints, exit code 0
• Failure: Python traceback with error message, exit code 1

Common errors:

• DeckConflictError — labware placement conflict
• LabwareDefinitionDoesNotExist — invalid labware name
• OutOfTipsError — not enough tips for the protocol
• LiquidHeightUnknownError — .meniscus() called on a well without load_liquid() — see reference-source-map.md
• IncompatibleAddressableAreaError — wrong slot for robot type

Analysis

Produces structured JSON with predicted commands, labware layout, pipettes, modules, and errors. Use for deep inspection or CI validation. Also the only way to verify protocols with CSV RTPs.

# Standard
api/.venv/bin/python -m opentrons.cli analyze tmp-protocols/my_protocol.py \
    --check --human-json-output=-

# With custom labware — pass the JSON file(s) as extra positional arguments
api/.venv/bin/python -m opentrons.cli analyze \
    tmp-protocols/my_protocol.py \
    tmp-custom-labware/my_custom_plate.json \
    --check --json-output=-

# With primitive RTP values (int, float, bool, str)
api/.venv/bin/python -m opentrons.cli analyze tmp-protocols/my_protocol.py \
    --check --json-output=- \
    --rtp-values='{"sample_count": 8, "dry_run": false}'

# With CSV RTP file
api/.venv/bin/python -m opentrons.cli analyze tmp-protocols/my_protocol.py \
    --check --json-output=- \
    --rtp-files='{"transfer_map": "tmp-csv/transfer_map.csv"}'

# Combined: custom labware + CSV RTP
api/.venv/bin/python -m opentrons.cli analyze \
    tmp-protocols/my_protocol.py \
    tmp-custom-labware/my_custom_plate.json \
    --check --json-output=- \
    --rtp-files='{"transfer_map": "tmp-csv/transfer_map.csv"}'

Analysis Options

Custom labware in analyze: there is no -L flag. Pass each labware JSON as an extra positional file argument. The analyze command recognizes them by their JSON schema and registers them before running.

JSON Output Structure

{
  "createdAt": "...",
  "result": "ok",
  "robotType": "OT-3",
  "config": {"protocolType": "python", "apiVersion": [2, 28]},
  "metadata": {"protocolName": "..."},
  "commands": [...],
  "labware": [...],
  "pipettes": [...],
  "modules": [...],
  "liquids": [...],
  "errors": [],
  "runTimeParameters": [...]
}

Key fields: result ("ok" / "not-ok" / "parameter-value-required"), errors (empty = valid), commands (full ordered command list).

With Runtime Parameters

api/.venv/bin/python -m opentrons.cli analyze protocol.py \
    --check --json-output=output.json \
    --rtp-values='{"sample_count": 48, "dry_run": false}'

# CSV parameter files
api/.venv/bin/python -m opentrons.cli analyze protocol.py \
    --check --json-output=output.json \
    --rtp-files='{"plate_map": "/path/to/map.csv"}'

Standard Verification Workflow

Before running anything, check whether the protocol defines add_parameters(). If it does, skip simulate entirely and go straight to analyze — then tell the user why.

# 1. Quick check — simulate (only if protocol has NO add_parameters())
api/.venv/bin/opentrons_simulate tmp-protocols/my_protocol.py

# 1b. Quick check — simulate with custom labware (still no RTPs)
api/.venv/bin/opentrons_simulate tmp-protocols/my_protocol.py \
    -L tmp-custom-labware/

# 2. Deep check — analyze (required for any protocol with add_parameters())
api/.venv/bin/python -m opentrons.cli analyze \
    tmp-protocols/my_protocol.py \
    [tmp-custom-labware/my_plate.json] \
    --check --human-json-output=- \
    [--rtp-values='{"key": value}'] \
    [--rtp-files='{"csv_param": "tmp-csv/file.csv"}']

Decision guide:

Snapshot Testing Integration

For protocols to be tracked for regression, use analyses-snapshot-testing/:

cd analyses-snapshot-testing/

# Naming: {Robot}_{Status}_{Version}_{Pipettes}_{Modules}_{Description}.py
# Example: Flex_S_v2_28_P1000_GRIP_SerialDilution.py

make prep
make snapshot-test-update PROTOCOL_NAMES=Flex_S_v2_28_P1000_GRIP_SerialDilution OVERRIDE_PROTOCOL_NAMES=none

See the analyses-snapshot-testing skill for full details.

Keeping This Skill Current

When simulate or analyze surfaces a new error pattern, constraint, or CLI behavior that isn't already documented here, add it to the Troubleshooting section or update the relevant command example. The next person hitting the same issue will thank you.

Troubleshooting

api/.venv/ doesn't exist

make -C api setup

Simulation succeeds but analysis shows errors

Analysis is stricter. Check the errors array in JSON output for details.

Protocol works in simulation but fails on robot

Simulation doesn't verify physical constraints: actual tip presence, liquid volumes, module calibration, or physical deck geometry.

Slow runs

If you accidentally used uv run instead of the venv binaries, it checks/rebuilds the venv each time. Switch to api/.venv/bin/... for instant invocations.