Kuberwastaken/claurst · error

rmcp list_resources failed

Error message

rmcp list_resources failed: {}

What it means

Raised in `RmcpClientBackend::list_resources` when the rmcp peer's `list_all_resources()` future fails during the `resources/list` round-trip. Like the other rmcp peer wrappers, any transport failure or JSON-RPC error response from the MCP server is re-wrapped with a uniform message so the caller sees which backend operation failed. The original rmcp error text follows the colon.

Solutions

  1. Check the inner error: 'method not found' means the server has no resources capability — treat the list as empty.
  2. Reconnect the MCP session and retry if the transport/session closed.
  3. Verify the server advertises the resources capability in its initialize response.
  4. Check server-side logs if the enumeration itself failed.

Example fix

// before: unconditional listing
let resources = backend.list_resources().await?;
// after: tolerate servers without the resources capability
let resources = match backend.list_resources().await {
    Ok(r) => r,
    Err(e) if e.to_string().contains("method not found") => Vec::new(),
    Err(e) => return Err(e),
};
Defensive patterns

Strategy: try-catch

Validate before calling

fn server_supports_resources(init_caps: &ServerCapabilities) -> bool {
    init_caps.resources.is_some()
}

Try / catch

match backend.list_resources().await {
    Ok(resources) => resources,
    Err(e) if e.to_string().contains("method not found") => Vec::new(),
    Err(e) => return Err(e.into()),
}

Prevention

When it happens

Trigger: Calling `list_resources` when the server rejects `resources/list`: server lacks the resources capability (JSON-RPC 'method not found'), the session is closed or stale, the transport failed mid-request, or the server errored enumerating its resources.

Common situations: Connecting to an MCP server that only exposes tools (very common — many servers skip resources); server restarted between connect and the listing call; legacy SSE endpoint no longer valid; a resource provider on the server side panicking during enumeration.

Understand the failure class

Background: "API request failed": what wrapped HTTP errors from external APIs mean and how to find the real cause — this error's family across 29 libraries.

Related errors

AI-assisted analysis of Kuberwastaken/claurst@b0637c97ec (2026-09-10). Data as JSON: /api/errors/69eed04f3f36f994. Report an issue: GitHub.

Appendix: source

Thrown at src-rust/crates/mcp/src/rmcp_backend.rs:534

    ) -> anyhow::Result<CallToolResult> {
        let mut params = rmcp_model::CallToolRequestParams::new(name.to_string());
        if let Some(arguments) = arguments {
            params = params.with_arguments(json_value_to_object(arguments)?);
        }
        let result = self
            .peer
            .call_tool(params)
            .await
            .map_err(|e| anyhow::anyhow!("rmcp call_tool '{}' failed: {}", name, e))?;
        Ok(convert_call_tool_result(result))
    }

    async fn list_resources(&self) -> anyhow::Result<Vec<McpResource>> {
        let resources = self
            .peer
            .list_all_resources()
            .await
            .map_err(|e| anyhow::anyhow!("rmcp list_resources failed: {}", e))?;
        Ok(resources.into_iter().map(convert_resource).collect())
    }

    async fn read_resource(&self, uri: &str) -> anyhow::Result<ResourceContents> {
        let result = self
            .peer
            .read_resource(rmcp_model::ReadResourceRequestParams::new(uri.to_string()))
            .await
            .map_err(|e| anyhow::anyhow!("rmcp read_resource '{}' failed: {}", uri, e))?;
        let first = result
            .contents
            .into_iter()
            .next()
            .ok_or_else(|| anyhow::anyhow!("rmcp read_resource '{}' returned no contents", uri))?;
        Ok(convert_resource_contents(first))
    }

    async fn list_prompts(&self) -> anyhow::Result<Vec<McpPrompt>> {

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