How to parse a GPS NMEA log
- Paste complete sentences, one per line, or try the sample messages.
- Choose Parse sentences. Review the checksum counts and select a line.
- Read the raw and decoded fields together. Empty fields remain unavailable, not zero. Errors and receiver-reported invalid fixes stay visible.
- Copy the original or decoded JSON, or preview and copy checksum-only corrections. Editing the input clears old results; parse again to refresh.
Supported sentence types
GGA: UTC time, position, fix quality, satellites used, HDOP, mean-sea-level altitude, and geoid separation. RMC: time, receiver status, position, speed, true course, date, and optional mode/navigation status.
GSA: fix dimension, twelve active-satellite slots, and PDOP/HDOP/VDOP. GSV: message part and up to four satellite groups, with optional signal ID. VTG: course and speed in knots and km/h.
Mixed-GNSS and other talker prefixes are retained. Proprietary and unsupported sentences, including !-prefixed messages, receive checksum inspection and raw-field display only. AIS payloads are not decoded.
NMEA coordinates and UTC dates
Latitude uses ddmm.mmmm; longitude uses dddmm.mmmm. Decimal degrees equal degrees plus minutes divided by 60, with south and west negative. For example, 4807.038,N becomes 48.11730000°. These are not plain decimal-degree inputs.
Times are UTC, not your local timezone. RMC dates use DDMMYY and do not encode a century; the parser deliberately does not guess one. Leap-second time notation is retained raw but not decoded. Course over ground describes travel direction, not a compass heading.
How the NMEA checksum works
Start at zero and XOR each ASCII byte between the sentence's starting delimiter and the asterisk, including all commas and empty-field delimiters. Write the result as two hexadecimal digits. For the GGA sample shown in the input placeholder, the checksum is 47.
A missing or mismatched checksum does not stop field inspection, but the result is explicitly unverified. Malformed framing cannot be corrected safely. Some receivers exceed the conventional 82-character limit; these messages receive a warning rather than automatic rejection within this tool's processing limits.
Questions and limitations
Does a matching checksum mean the GPS fix is valid?
No. Read the receiver's fix/status fields. Even an active fix and a matching checksum do not establish accuracy or suitability for navigation. DOP is a geometry indicator, not an error distance.
Does this combine multipart GSV messages?
No. Each line is inspected independently. A pasted batch may contain different epochs, receivers, constellations, or signals; combining it would risk inventing a single satellite view.
Are optional fields and receiver extensions supported?
The common optional RMC mode/navigation status, GSA system ID, GSV signal ID, and VTG mode are displayed. Unknown codes and extra fields remain visible, with warnings. Consult your receiver's manual for version-specific meanings; this is not certification against the licensed NMEA standard.
Are my coordinates sent anywhere?
The parser does not upload or save your pasted log. Copy and download are explicit actions. The site's shared analytics is unchanged and is not given your input or decoded results.
Public manufacturer references
Field interpretation follows Trimble's common NMEA message elements and its public GGA, RMC, GSA, GSV, and VTG documentation. u-blox's public interface description documents version-dependent extensions. NovAtel distinguishes NMEA's 8-bit XOR checksum from its other CRC formats.