ZwiftPower ZRS Browser Extension Updated: ZRS History, Power Curves, + More

A few months ago, I wrote about the ZwiftPower ZRS Browser Extension. Since then, it has undergone substantial upgrades, including an incredibly detailed new profile page that charts your ZRS history! So I reached out to the creator (who goes by the pseudonym “int” on socials) for a look at what has changed, including a detailed list of new features. Here’s what I received…

From the Creator

Since the last Zwift Insider article, the extension has grown quite a bit.

The very first version took only a few hours to build. I probably spent almost the same amount of time writing my response to Zwift Insider when he first reached out. It was just a simple script to inject ZRS scores into ZwiftPower event pages. Nothing fancy.

Back then, I mentioned the article may “give the project new life.” Well, it did. The article brought in more users, and with them came requests. Profile page support. History graphs. More detailed analytics. Each feature request led to another and the codebase went from a few hundred lines to… well, something more substantial.

So here we are again, writing another response after Eric reached out asking if I had any “juicy details” to share.

Recent Development

The active users of the extension already know that not everything went smoothly.

The first major update went live and didn’t last long. Users started processing their lifetime event histories, and some corrupt Zwift events from years ago triggered an infinite fetching loop.

The combination—hundreds of users processing thousands of events each, plus the bug causing endless retries—created an API spike. I fixed the bug immediately after it was reported, but the damage was already done. Zwift decided to enforce authentication requirements, breaking the extension for everyone.

I reached out to Zwift, acknowledged I should have coordinated beforehand, and didn’t hear back. So a few days later I implemented a workaround that captures the user’s Zwift token (with the user’s permission, of course) to get things going again.

Besides restoring functionality, authentication unlocked additional API endpoints that made most of the newly added features possible. In the end, the authentication enforcement turned out to be a good thing.

Looking Forward

The extension serves a niche within the Zwift community, and I’m glad people find it useful. There’s still plenty to improve—I won’t be running out of ideas anytime soon. I appreciate everyone who’s taken the time to report bugs, suggest features, or simply tell your buddy about it. And special thanks to the testers.

Hopefully, Eric will have a reason to check in again down the road.

If you have thoughts or ideas, feel free to reach out.

(That goes for Zwift, too. It would be cool if we could implement proper OAuth2 authentication and you could relax your CORS restrictions a little bit.)

ZRS Extension: Technical Overview

What ZRS Extension Does

The ZRS extension enhances ZwiftPower.com by adding ZRS (Zwift Racing Score) data, performance analytics, and racing statistics to profile and event pages. The extension operates as a fully decentralized system, running entirely within the browser environment. All data processing, storage, and analytics occur locally on the user’s device, with no external servers or databases involved.

Key Capabilities

• ZRS Score Integration: Adds ZRS scores and changes directly into ZwiftPower event tables
• Performance Analytics: Power analysis, phenotype detection, activity tracking
• Racing Statistics: Head-to-head comparisons, ranking points visualization, ZRS history graphs

The Profile Dashboard

Layout Overview

The extension redesigns the ZwiftPower profile page with a three-column dashboard layout:

• Left Column: Athlete profile, Zwift stats, and power analysis
• Middle Column: Activities, and context-aware panels (power curve for personal profiles, head-to-head for opponents)
• Right Column: ZRS score history and race ranking points

Left Column: Athlete Profile & Performance

Main Profile Panel

Identity Section:

• Profile picture (or ZRS logo placeholder if no picture)
• Zwift in-game name
• Country flag and name (or “Zwifterland” fallback)
• Team name (clickable link if available)
• Platform links: Zwift.com, ZwiftRacing.app, Strava.com
• Follower count button (links to Zwift follower page)
• Bio button (displays rider biography in modal)
• Refresh button (navigates to ZwiftPower profile update page)

Overlays (on profile picture):

• Online indicator (if currently riding)
• Signup indicator (if upcoming registered events exist)

Athlete Stats Section:

• Profile: Gender and age (e.g., “M45”, “F33”)
• Height (cm) with variation tooltip
• Weight (kg) with variation tooltip
• Power source (Smart Trainer, Power Meter, zPower)

Racing Stats Panel:

• Category: Shows racing category with color-coded circle (Mixed and Women’s categories for female riders)
• ZRS: Current racing score (dual badge showing both current and MAX30 score for personal profiles)
• ZPoints and Ranking Points (metrics from ZwiftPower)
• zFTP: Functional threshold power in watts and W/kg
• Race count with win and podium rate in tooltip

All sections use category-based color theming (A+ = black, A = red, B = green, etc.).

Zwift Stats Panel

Progression Subpanel:

• Level with progress bar showing percentage to next level
• XP (experience points)
• Current bike frame model
• Drops

Riding Stats Subpanel (toggleable between 30d/Year/Total):

• Distance (km)
• Elevation climbed (m)
• Longest ride (km)
• Highest climb (m)

Header: Shows total hours and “since [year]” (year joined Zwift)

Power Panel

Power Radar Chart:

• Spider web visualization for 7 durations (5s, 15s, 30s, 1min, 2min, 5min, 20min)
• Shows both 90-day recent bests and all-time bests
• Overlays intervals.icu distribution data (toggle between gender or gender-age data)
• Interactive hover tooltips for exact values
• Toggle between watts and W/kg display modes

Duration Power Table:

• Numerical values for all durations plus FTP

Power Skills:
Three skill categories rated 0.0-10.0 based on percentile vs. intervals.icu distribution data:

• Sprint (5s, 15s, 30s)
• Attack (1min, 2min, 5min)
• Endurance (20min)
• General average score

Phenotype Detection:
Analyzes power distribution to classify rider into one of six types:

• Sprinter: Explosive short-duration power specialist (example: Mark Cavendish)
• Puncheur: 1-5 minute effort specialist (example: Mathieu van der Poel)
• Time Trialist: High sustained raw watts (example: Stefan Küng)
• Climber: High sustained W/kg (example: Nairo Quintana)
• Allrounder: Balanced across all durations (example: Tadej Pogačar)
• Pursuiter: High sprint and endurance, weak middle durations (example: Dan Bigham)

Middle Column: Context-Aware Analytics

The middle column displays different panels depending on whether viewing your own profile or an opponent’s profile.

Activity Panel

4-Week Calendar Grid:

• Last 28 days displayed as 4 weeks × 7 days
• Activity type icons color-coded by type (race, TT, group workout, group ride, etc.)
• Signup indicator (calendar icon) for upcoming registered events
• Weekly totals column

Scrollable Activity List:

• Chronological list of recent activities
• Background colors match activity type
• Clickable rows link to detailed activity page on zwift.com

1v1 Head-to-Head Panel (Opponent Profile)

Summary Metrics:

• Total shared events (same category races)
• Win/loss record
• Win rate percentage
• Average position advantage/disadvantage (% of field size)

Match History List:

• Scrollable list of all shared events
• Each row shows: event name, category circle, zwift ingame name, date
• Win/loss indicator (green/red)
• Clickable to view full event results

This feature requires complete lifetime event processing for the user’s own profile. First-time processing may require a few minutes depending on race history volume.

Power Curve Panel (Personal Profile Only)

Power Curve Graph:

• Line chart of best power outputs across all durations
• X-axis: Duration (logarithmic scale, 5s to 60min)
• Y-axis: Power (toggle between watts and W/kg)
• Shows only 90-day best (all-time data from Zwift API is unreliable)

Power Zone Background:

Shaded regions showing Zwift’s 7 power zones based on FTP percentage:

• Z1 Recovery (<60% FTP) – Gray
• Z2 Endurance (60-75%) – Cyan
• Z3 Tempo (75-89%) – Green
• Z4 Threshold (89-104%) – Yellow
• Z5 VO2 Max (104-118%) – Orange
• Z6 Anaerobic (118-200%) – Red
• Z7 Sprint (>200%) – Magenta

Interactive hover shows exact values at specific durations.

Right Column: Racing Performance

ZRS Graph Panel

Dashboard Metrics (7 cells):

• Current ZRS score
• Lowest score in last 90 days
• Highest score in last 90 days
• Net change (total gains/losses)
• Average change per event
• Worst single event loss
• Best single event gain
• Eligible race categories (hexagon badges, clickable to show upcoming events in that category)

Score History Graph:

• Time-series line chart showing ZRS progression (last 90 days)
• X-axis: Time with month labels
• Y-axis: ZRS score (0-1000)
• Background diagonal stripe patterns show category boundaries:
• Range 1: E (0-159), D (160-269), C (270-389), B (390-509), A (510-649)
• Range 2: E (0-209), D (210-329), C (330-449), B (450-569), A (570-724)
• Advanced: A+ (650-1000)
• Data points colored by category of event
• Trophy icons displayed to highlight podium finishes
• Hover tooltips show event name, date, score change, rank, field size
• Smooth connecting lines show trajectory

Race Ranking Panel

Ranking Points Bar Chart:

• X-axis: Chronological event sequence (oldest to newest)
• Y-axis: Ranking points earned (0-100)
• Each bar represents one ranked event
• Bar height = points earned
• Bar color = event category
• Top 5 events highlighted with filled background (these count toward ranking)
• Hover tooltips: event name, category, exact points, rider’s position

ZwiftPowers’s ranking system uses top 5 events from last 90 days. This visualization shows which races currently contribute to the ranking score.

Event Pages & Table Enhancements

ZwiftPower Table Enhancement

New ZRS Columns

• “ZRS” column displaying current score
• “±” column showing score change from the event
• Score change type indicators (floor increased, at floor)

ZRS Prediction Accuracy

The extension calculates how accurately ZRS scores predicted the actual race results using Spearman’s rank correlation coefficient (ρ):

• Compares predicted finishing order (based on pre-race ZRS scores) vs. actual results
• Calculated per category, then weighted by field size for overall accuracy
• Displayed as percentage: +100% = perfect prediction, 0% = random, -100% = inverse
• Color-coded indicator: green (≥60%), yellow (30-59%), red (<30%)

This metric provides insight into whether the race results aligned with pre-race ZRS expectations (an objective way of determining how well ZRS is actually working).

Non-ZRS Event Detection

Events where no ZRS changes occurred (workouts, group rides, etc.) are identified and labeled with a “Non-ZRS Event” indicator, preventing confusion when no scores appear.

Under the Hood: Data Sources & Integration

The extension aggregates data from multiple sources to provide comprehensive racing analytics:

ZwiftPower

Profile and event metadata is extracted from ZwiftPower.com through two complementary methods:

Scraping: The extension reads visible event tables directly from the rendered page HTML to extract:

• Event IDs and dates
• Race categories and results
• Rider rankings and positions
• Event names and metadata

Interception: When ZwiftPower loads profile data via API calls, the extension intercepts these requests to capture:

• Complete event history
• ZwiftPower-specific metadata (race types, categories)
• Signup information
• Event results

Zwift Official API

ZRS scores and detailed race results come directly from Zwift’s official API.

Race Results Endpoint:

• ZRS scores (current and change)
• Score change types (floor increased, etc.)
• Subgroup assignments
• Field sizes and rankings

Profile Endpoint:

• Rider name and basic info
• Weight, height, FTP
• Country and platform data

Activities Endpoint:

• Recent ride history
• Activity types (races, group rides, workouts)
• Performance metrics

Max30 Endpoint: (personal profile only)

• Only accessible for the authenticated user’s own profile

Power Curve Endpoint:

• Complete power profile data across all durations
• Recent best efforts (5s, 15s, 30s, 1min, 2min, 5min, 10min, 20min, 60min, etc.)
• Only accessible for the authenticated user’s own profile

Intervals.icu Power Data

Benchmark power data embedded directly in the extension from Intervals.icu’s analysis of thousands of real cyclist power files:

Coverage: Age/gender-specific percentile data for:

• Multiple age brackets (Under 23, 30-34, 40+, 50+, 60+, etc.)
• Male and female categories
• Seven key durations (5s, 15s, 30s, 1min, 2min, 5min, 20min)

Questions or Comments

Share your thoughts below!