Built for
Routes with story
Import, style, narrate, and export without leaving the browser.
Agents
Let an agent build the replay. You just drop the folder.
Marking twenty aid stations by hand, or ordering ten days of GPX files and sizing each one, is an hour of clicking. Describe it to an AI agent instead: it writes a small recipe next to your routes, you drop the folder here, and the map does the rest.
Best with
Rich GPX files
Tracks with timestamps and elevation make the replay immediately stronger.
Step 1
Ask your agent
Tell it what you want in plain words: the aid stations from a race page, the huts you slept in, or the order of your days. Point it at trailreplay.com/llms.txt so it knows the format.
Step 2
It writes a recipe
A short JSON file saved next to your GPX files. It describes places by kilometre, such as “the aid station at km 6.5,” never by coordinates because the map works those out itself.
Step 3
You drop the folder
Select the recipe and the GPX files together and drop them on TrailReplay. Routes, order, timing, pins and captions all arrive at once, ready to play.
Copy this
What to say to your agent
Any coding agent that can read a web page and write a file will do. This is enough to get a working recipe back.
Prompt
Read https://trailreplay.com/llms.txt and the format spec it links to. Then write a recipe.json in this folder for the GPX files here, following what I describe below. Do not compute coordinates. Anchor everything by kilometre and let the app resolve it. Before setting up video export, ask me whether I want a designed cover image shown for the first second of the video; wait for my answer and set includeCover accordingly. If I want a photo cover, name the image files in photoSlots and include those files with the recipe.
Then say what you actually want: the aid stations off a race page, the huts you stayed in, a caption at the big climb.
Camera distance that matches the website
Follow Behind does not use raw map zoom. Recipes use the same distance positions as the website slider, from 0 for the widest view to 100 for the closest.
| Website preset | Recipe level | Result |
|---|---|---|
| Far | 0 | The widest Follow Behind view. |
| Medium | 33 | The balanced default. |
| Close | 66 | Keeps the camera nearer the marker. |
| Very close | 100 | The tightest Follow Behind view. |
Exact slider stops: 0, 11, 22, 33, 49.5, 66, 83, and 100. Lower is farther away; higher is closer.
Two things worth handing over
Both recipes below are real and runnable. Neither contains a single coordinate.
A race with aid stations
Every aid station, at the right kilometre
A race page lists its aid stations by kilometre. Placing them by hand means finding each point on the map, adding a note, and typing the contents four times over. An agent reads the page and writes them all.
Each station becomes a card that rises as the runner approaches it and fades once past. It reads as something met, not a pin left on the map.
recipe.json
{
"name": "Valls del Freser XTREM 32K",
"tracks": [{ "file": "xtrem.gpx", "color": "#E86F51" }],
"landmarks": [
{ "auto": "start-finish", "type": "trailhead", "icon": "town" }
],
"annotations": [
{ "km": 6.5, "title": "Avituallament 1 - Collet de Barraques" },
{ "km": 13, "title": "Avituallament 2 - Torrent Gros" },
{ "km": 17, "title": "Avituallament 3 - Dòrria" },
{ "km": 25, "title": "Avituallament 4 - Les Casetes" }
]
}A ten-day trip
Ten files, in order, correctly sized
Ten days of walking is ten GPX files, out of order, and ten decisions about how long each should last on screen. Do it by hand and a 35 km day gets the same seconds as an 8 km one.
Files ordered by their own timestamps, screen time shared by distance, and a pin at every place you slept, worked out from where one day ends and the next begins.
recipe.json
{
"name": "Ten days across the Pyrenees",
"tracks": { "files": "*.gpx", "order": "chronological" },
"landmarks": [
{ "auto": "start-finish", "type": "trailhead" },
{ "auto": "overnight-stops", "type": "hut", "icon": "shelter" }
]
}Getting the files
It can help you get the routes too
You do not need the GPX files in hand before you start. Ask, and a good agent works through these in order. The first two cost you nothing.
- 1A public link
Race organisers and clubs publish GPX files on their own site. If you name the race, the agent can usually just fetch it.
- 2A folder you already have
Your Downloads folder, or a trip folder. It reads what is there and puts the days in order by their own timestamps.
- 3An archive you request
For everything at once, Strava and Garmin will email you your whole history. It arrives as a mix of GPX, FIT and TCX. TrailReplay reads GPX, KML and FIT, so only TCX needs converting.
- 4Your own browser
An agent that can use your browser presses Export GPX on a page you are already signed in to. Fine for a few activities, not for two hundred.
What it should never do: ask for your password, work around a paywall or a private setting, or scrape behind a login. If a provider wants you to click the button yourself, the agent should tell you which button.
Per-provider export steps →It checks the work
You do not have to take the agent’s word for it
When the folder lands, TrailReplay lists everything it placed: the kilometre along its route, the seconds it is on screen, and how far the moving marker is from each place at the moment it appears.
7.1 km 23-28s Les Casetes 25.0 km 42-47s Les Casetes marker 4.1 km away
That last number should be metres. Anything more means the entry is timed to the wrong part of the replay, and the app says so before you ever press play.
For your agent
Send it here. Everything it needs is on one origin, and none of it requires an install or an account.