> For the complete documentation index, see [llms.txt](https://docs.tumbler.app/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.tumbler.app/getting-started/fetch-url.md).

# Validate the subscription URL

## Who this is for

Provider teams that already have a subscription link or are preparing an endpoint for Tumbler.

## What you can do

* Check that the existing URL is compatible with the backend fetcher.
* Understand the minimum requirements for domain, port, redirects, and stability.
* Decide whether to show the raw URL to the user or wrap it in `crypt3`.

## Examples

* `https://provider.example.com/sub/u_123`
* `https://cdn.provider.example.com/sub/u_123`
* `https://provider.example.com/sub/u_123?v=2026-07-01`, if the version is deterministic.

## See also

* [getting-started/add-link.md](/getting-started/add-link.md)
* [operations/fetcher-http-contract.md](/subscription-contract/fetcher-http-contract.md)
* [subscription/response-formats.md](/subscription-contract/response-formats.md)
* [subscription/metadata.md](/subscription-contract/metadata.md)
* [operations/mirrors-and-migration.md](/after-first-launch/mirrors-and-migration.md)

## What is a subscription URL

A subscription URL is the address from which the Tumbler backend downloads the provider configs.

The user can receive this URL directly only in the raw HTTPS scenario. In the `crypt3` scenario the user sees only an encrypted source link, and the backend calls the real URL after decryption.

## Recommendations

* Use HTTPS. HTTP is acceptable only as an intentional compatibility case.
* Keep the port standard: 443 for HTTPS or 80 for HTTP.
* Do not use `username:password@host` in the URL: credentials leak into logs, referrers, and error messages.
* Do not depend on cookies or interactive authorization. The backend fetcher performs a normal server-side `GET`.
* If the link is one-time-use or sensitive, do not give it to the user as raw HTTPS. Use `crypt3`.
* Keep the path long-lived. If you move the endpoint, use `new-url`, `new-domain`, mirrors, or a stable redirect.
* The response should stay identical for repeated fetcher requests until the subscription changes.
* For larger providers, enable `ETag`/`Last-Modified` so the backend can use `304 Not Modified`.

## How this relates to the add link

Raw HTTPS scenario:

```
subscription URL: https://provider.example.com/sub/u_123
add link:         tumbler://add?link=https%3A%2F%2Fprovider.example.com%2Fsub%2Fu_123
```

crypt3 scenario:

```
real URL:         https://provider.example.com/sub/u_123
source link:      schema://crypt3/<token>
add link:         tumbler://add?link=schema%3A%2F%2Fcrypt3%2F...
```

## Minimum response requirements

* HTTP status `200 OK` for the current subscription version.
* `Content-Type: text/plain; charset=utf-8` or `application/json; charset=utf-8`.
* UTF-8 without BOM.
* The body contains at least one valid VLESS node or a JSON/Xray/sing-box object from which a VLESS outbound can be extracted.
* The body size does not exceed fetcher limits. Recommended size is up to 200 KB; the hard limit is documented in [fetcher-http-contract.md](/subscription-contract/fetcher-http-contract.md).


---

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