21st Agents SDK vs Backstage vs Convai vs Invoice Ninja
| Attribute | ||||
|---|---|---|---|---|
| Category | Developer Tools | Developer Tools | AI Agents & Assistants | Billing & Invoicing |
| Pricing | Paid | Free tier | Free tier | Free tier |
| Starting price | $6/month | — | $5/month | $140/month |
| Free tier | No | Yes | Yes | Yes |
| Free trial | No | Unknown | Yes | No |
| Deployment | — | — | — | Cloud |
| API available | Unknown | Unknown | Unknown | Unknown |
| Platforms | — | — | — | ios, android, windows, linux |
| Certifications | — | — | — | — |
| Integrations | 1 | 3 | — | 1 |
| Company | — | — | — | — |
| Feature attributes | ||||
Also consider
Unknown values show as “Unknown”/“—”. Nothing is inferred — see each tool page for sources.