# Atlas webfetch error: URL must start with http:// or https:// > Pass a full absolute URL including the scheme: Atlas WebFetchTool validates the scheme first, so file://, data:, and bare hostnames are refused before the permission prompt. Atlas webfetch fails with URL must start with http:// or https:// because WebFetchTool validates the scheme before asking for the webfetch permission, so file://, data:, and bare hostnames are refused up front. The fix is to pass a full absolute URL including the scheme. If you were given a bare domain, prefix it with https://. To read a local file, use the read tool, not webfetch. ## Symptom The webfetch tool fails with: URL must start with http:// or https://. The call stops immediately, no request leaves the machine, and no webfetch permission prompt is shown. ## Cause WebFetchTool validates the scheme before asking for the webfetch permission, so file://, data:, and bare hostnames are refused up front, before any network request or permission check happens. ## Fix 1. Pass a full absolute URL including the scheme, for example https://example.com/docs rather than example.com/docs. 2. If you were given a bare domain, prefix it with https:// before handing it to webfetch. 3. To read a local file, use the read tool, not webfetch, because WebFetchTool refuses file:// and data: URLs during scheme validation. 4. Re-run the call; the permission prompt only appears once the URL passes validation. ## Why does Atlas report URL must start with http:// or https:// Atlas reports URL must start with http:// or https:// because WebFetchTool validates the scheme before asking for the webfetch permission. In 2026 that check runs first, so file://, data:, and bare hostnames are refused up front, before the request is made or the permission prompt appears. The error is a validation result, not a network failure. WebFetchTool inspects the URL string you passed, sees that it does not begin with http:// or https://, and stops. Nothing is dialed, nothing is downloaded, and the allow, ask, and deny permission rules are never consulted, because every Atlas tool call is permission-gated only after the tool's own arguments are considered valid. That ordering is why the message arrives instantly instead of after a hang. Three input shapes trigger it in practice: a file:// URL, a data: URL, and a bare hostname such as docs.example.com with no scheme in front of it. ## How to fix the Atlas webfetch invalid URL error Fix the Atlas webfetch error in 1 step: pass a full absolute URL including the scheme. If you were given a bare domain, prefix it with https://. For anything on local disk, use the read tool instead, because WebFetchTool refuses file:// during scheme validation, before the webfetch permission prompt ever appears. Rewrite the argument so the very first characters are http:// or https://. A bare domain like api.example.com becomes https://api.example.com. A path copied from a browser address bar that dropped the scheme becomes https:// plus that path. Once the URL passes validation, webfetch proceeds to the permission stage, where Atlas checks the call against your allow, ask, and deny rules and prompts if the rule set says ask. There is a caveat worth stating plainly: adding https:// makes the URL valid, but it does not make the host reachable. Validation only proves the shape of the string, not that the server exists. ## How to read a local file in Atlas instead of using webfetch Use the Atlas read tool instead of webfetch for anything on local disk. WebFetchTool accepts only 2 schemes, http:// and https://, and refuses file:// and data: URLs during scheme validation, so a local path will never fetch, no matter how it is quoted. Atlas read opens the file directly. Developers commonly hit URL must start with http:// or https:// while trying to point webfetch at a file on their own machine, either as file:///home/me/spec.html or as a raw path. Neither passes the scheme check. The read tool is the correct instrument for local content, and Atlas pairs it with grep and glob for locating files. For code specifically, Atlas also searches with hybrid semantic and keyword retrieval fused by reciprocal rank fusion, indexing by AST declarations using tree-sitter rather than blind line windows, so you rarely need a URL at all to answer a question about the repository in front of you. ## How to verify the Atlas webfetch fix worked Verify the Atlas webfetch fix by re-running the call. The permission prompt only appears once the URL passes validation, so there is exactly 1 signal to watch for: Atlas asking for webfetch permission, rather than printing URL must start with http:// or https://, means the scheme check passed and the request is proceeding. The permission prompt is the confirmation. Because WebFetchTool validates the scheme before asking for the webfetch permission, the prompt is proof that validation succeeded. If your rules already allow webfetch, no prompt appears and you will instead see the fetched content come back. If you still see the same error text after editing the URL, the string in the tool call is not the string you think it is: check for a leading space, a stray quote, or a scheme that was stripped when the value was interpolated from a variable or a previous tool result. ## Which URL schemes does Atlas webfetch accept Atlas webfetch accepts exactly 2 URL schemes: http:// and https://. WebFetchTool refuses everything else, including file:// URLs, data: URLs, and bare hostnames with no scheme at all. The check runs before the webfetch permission prompt, so a refused URL never reaches your allow, ask, and deny rules. Keep the accepted set in mind when you build URLs programmatically or when an earlier step in a session hands webfetch a value it scraped from documentation. Anything that is not an absolute http:// or https:// URL is rejected up front. That includes protocol-relative URLs that start with two slashes and links copied without their scheme. The rule is simple enough to apply mechanically: if the string does not literally begin with http:// or https://, webfetch will not take it, and the fix is either to add the scheme or to switch to the read tool for local content. ## FAQ ### how to fix URL must start with http:// or https:// in Atlas Pass a full absolute URL including the scheme. Atlas WebFetchTool validates the scheme before asking for the webfetch permission, so example.com must be written as https://example.com before the call will run. ### can Atlas webfetch open a file:// URL No. Atlas WebFetchTool refuses file:// and data: URLs during scheme validation. To read a local file, use the read tool, not webfetch. ### why does Atlas webfetch fail before showing a permission prompt WebFetchTool validates the scheme before asking for the webfetch permission. An invalid URL fails validation first, so the allow, ask, and deny rules are never reached and no prompt is shown. ### does Atlas webfetch accept a bare domain like example.com No. Bare hostnames are refused up front. Prefix the domain with https:// so the URL begins with an accepted scheme, then re-run the call. ### how do I know the Atlas webfetch URL error is fixed Re-run the call. The permission prompt only appears once the URL passes validation, so a prompt for webfetch, or returned content when webfetch is already allowed, confirms the scheme check passed. ### what should I use instead of Atlas webfetch for local files Use the Atlas read tool. It opens files on disk directly, while webfetch is limited to absolute http:// and https:// URLs. --- Canonical HTML: https://runatlas.sh/resources/troubleshooting/webfetch-invalid-url Source of truth: aeo_pages row `/resources/troubleshooting/webfetch-invalid-url` (segment: Troubleshooting) (this file is generated from it, never hand-edited). Licence: Atlas is proprietary with a free core. It is not open source and there is no public source repository.