resource URI ' ' was not advertised by any running MCP…

Error message

resource URI '{}' was not advertised by any running MCP server

What it means

read_resource_by_uri looks up a resource URI among resources advertised by running servers. For a standard (non server-prefixed) URI, if no running server advertised it (and no server-embedded URI matches a running client), the library reports the URI is unknown.

Solutions

Verify the URI against resources advertised by the running server
Ensure the owning MCP server is running and registered
Re-fetch the resource list after servers start

Example fix

// before
manager.read_resource_by_uri("file:///missing.txt", None)?
// after
let advertised = manager.list_resources()?;
if advertised.iter().any(|r| r.uri == uri) {
    manager.read_resource_by_uri(&uri, None)?
}

Defensive patterns

Strategy: validation

Validate before calling

if !manager.list_resources()?.iter().any(|r| r.uri == uri) { return Err("uri not advertised"); }

Try / catch

match manager.read_resource_by_uri(uri, server) { Err(e) if e.to_string().contains("was not advertised") => /* refresh resource list and retry */, other => other }

Prevention

Refresh the advertised resource list after server start/stop
Copy URIs from list_resources output rather than typing them
Check server liveness before resource reads

When it happens

Trigger: Calling read_resource_by_uri with a URI that no running server advertised via resources/list, or where the embedded server name in the URI does not correspond to a running client.

Common situations: Typo in the URI; server that advertised the resource has been stopped/unregistered; resource listing cached before the server started; passing a raw server-prefixed URI when the server is not running.

Understand the failure class

Background: 'Could not be found', 'does not exist', 'not found in database': the resource-not-found family when an ID, slug, key, or URI lookup comes back empty — this error's family across 20 libraries.

Related errors

AI-assisted analysis of Hmbown/CodeWhale@433685b202 (2026-09-15). Data as JSON: /api/errors/51236cdc0a26893e. Report an issue: GitHub.

Appendix: source

Thrown at crates/mcp/src/lib.rs:595

                .list_resources()?
                .iter()
                .any(|resource| resource.uri == uri)
            {
                matches.push(server_name.clone());
            }
        }

        match matches.len() {
            1 => self.read_resource(&matches[0], uri),
            0 => {
                // Preserve the pre-standard URI convention for clients whose
                // server does not implement resources/list.
                if let Some(server_name) = parse_server_from_uri(uri)
                    && self.clients.contains_key(&server_name)
                {
                    return self.read_resource(&server_name, uri);
                }
                bail!("resource URI '{uri}' was not advertised by any running MCP server")
            }
            _ => {
                matches.sort();
                bail!(
                    "resource URI '{uri}' is ambiguous across MCP servers: {}; pass the legacy \
                     server parameter to disambiguate",
                    matches.join(", ")
                )
            }
        }
    }

    /// Generate sandbox state update notices for all registered servers.
    pub fn update_sandbox_state(&self, sandbox_mode: &str, cwd: &str) -> Result<Vec<Value>> {
        let mut notices = Vec::new();
        for server_name in self.configs.keys() {
            notices.push(json!({
                "server_name": server_name,

View on GitHub (pinned to 433685b202)