If you're a solo developer who just shipped an app, you have a monetization problem. Not because your app isn't good — because the ad industry doesn't care about you yet.
The gatekeeping problem
Google AdSense is the default answer to "how do I put ads on my site." But AdSense has gotten increasingly selective. Sites with thin content, low traffic, or unconventional formats get rejected. The approval process takes days to weeks, and rejections often come with vague explanations. For a weekend project that gets 500 visitors a month, AdSense isn't an option.
Carbon Ads is beautiful. Developer-friendly. Non-intrusive. Also invite-only. Carbon hand-picks publishers that fit their premium advertiser base. If you're not already a well-known developer blog or tool site, the door is closed.
EthicalAds is open-source-friendly and privacy-respecting. Their minimum is 50,000 monthly pageviews. That's a high bar. Most indie apps never reach it.
BuySellAds requires you to list your site and wait for advertisers to pick you. Low-traffic sites sit in the marketplace indefinitely with zero bids.
The pattern is clear: every ad network optimizes for publishers who already have scale. If you're small, you don't exist.
The chicken-and-egg trap
This creates a vicious cycle for indie developers:
You can't earn money without traffic. You can't buy traffic without money. You can't get approved for an ad network without traffic you don't have. You can't grow without the distribution that ad revenue could fund.
So your app sits there. Maybe you tweet about it once. A few friends try it. Traffic flatlines. You move on to the next idea. The app dies.
This isn't a failure of the developer. It's a failure of the monetization infrastructure.
A network built for the small
Fill takes a fundamentally different approach. Instead of connecting publishers with outside advertisers (which requires scale to be attractive), Fill connects builders with each other.
When you add Fill to your app, you join a cross-promotion network. Your app shows ads for other builders' apps. Their apps show ads for yours. Every impression you serve earns credits. Every credit you spend drives traffic to your app from other apps in the network.
The requirements:
- Minimum traffic: None. Zero. Your first visitor starts earning.
- Approval process: None. Register via API or MCP, and you're in.
- Exclusivity: None. Run Fill alongside anything else.
- Content requirements: Don't be illegal or harmful. That's it.
The credit flywheel
Here's why cross-promotion is powerful at small scale:
Traditional advertising is a one-way cash drain. You pay money, you get impressions, end of transaction. Cross-promotion is circular. You show someone else's app to your users. They show your app to their users. Both apps grow. No money changes hands.
Credits are the unit of exchange. Earn them by showing ads. Spend them to promote. The network IS the distribution channel. Every app that joins makes every other app's promotion more effective, because there's more inventory to fill and more apps to discover.
When you're small, this matters more than dollars. A solo dev with 500 monthly visitors doesn't need $0.50/month from AdSense. They need 500 new users discovering their app from other apps. That's what Fill provides.
How Fill compares
| Fill | AdSense | Carbon Ads | EthicalAds | |
|---|---|---|---|---|
| Min. traffic | None | ~3K/mo | Invite-only | 50K/mo |
| Approval | Instant | Days-weeks | Application | Application |
| Revenue model | Credits + cash | Cash (CPM/CPC) | Cash (CPM) | Cash (CPM) |
| Cross-promotion | Built-in | No | No | No |
| Agent-native | MCP tools | No | No | No |
| Privacy | No cookies/tracking | Cookies + tracking | Minimal | No tracking |
| Best for | Indie / vibe-coded | Established sites | Dev/design blogs | OSS projects |
The existing ad networks serve an important role for publishers at scale. Fill serves the long tail — the thousands of small apps that existing networks ignore.