continuedev/continue · error · Error

No tool use found

Error message

No tool use found

What it means

While streaming an Anthropic response, an input_json_delta event (partial tool-call arguments JSON) arrived before any content_block_start established a tool_use block. The adapter tracks lastToolUseId/lastToolUseName from prior events; if either is unset, the stream is malformed and the adapter aborts. This almost always indicates an out-of-order or non-compliant event stream from the provider or a proxy.

Source

Thrown at packages/openai-adapters/src/apis/Anthropic.ts:411

          } as any;
          break;
        case "message_delta":
          const deltaEvent = rawEvent as RawMessageDeltaEvent;
          usage.completion_tokens = deltaEvent.usage?.output_tokens ?? 0;
          break;
        case "content_block_delta":
          // https://docs.anthropic.com/en/api/messages-streaming#delta-types
          const blockDeltaEvent = rawEvent as RawContentBlockDeltaEvent;
          switch (blockDeltaEvent.delta.type) {
            case "text_delta":
              yield chatChunk({
                content: blockDeltaEvent.delta.text,
                model,
              });
              break;
            case "input_json_delta":
              if (!lastToolUseId || !lastToolUseName) {
                throw new Error("No tool use found");
              }
              yield chatChunkFromDelta({
                model,
                delta: {
                  tool_calls: [
                    {
                      id: lastToolUseId,
                      type: "function",
                      index: 0,
                      function: {
                        name: lastToolUseName,
                        arguments: blockDeltaEvent.delta.partial_json,
                      },
                    },
                  ],
                },
              });
              break;

View on GitHub (pinned to 5522c6f44c)

Solutions

1. Inspect the raw SSE stream to confirm a content_block_start for a tool_use block precedes input_json_delta
2. Update or bypass any proxy/gateway between the client and Anthropic that rewrites stream events
3. If mocking Anthropic streams in tests, emit content_block_start (tool_use) before any input_json_delta
4. Pin/upgrade the openai-adapters package in case a schema change was fixed in a newer version

Example fix

// before (mock SSE missing block start)
const sse = `event: content_block_delta
data: {"type":"input_json_delta","partial_json":"{\"city\":"}

// after
event: content_block_start
data: {"type":"content_block_start","index":0,"content_block":{"type":"tool_use","id":"toolu_1","name":"get_weather","input":{}}}
event: content_block_delta
data: {"type":"content_block_delta","index":0,"delta":{"type":"input_json_delta","partial_json":"{\"city\":"}"}

try { for await (const chunk of api.chatCompletionStream(body, signal)) {} }
catch (e) { if (e.message === 'No tool use found') { logger.error('Malformed Anthropic stream — check proxy/fixtures', e); } throw e; }

When it happens

Trigger: Streaming a chat completion with tool use through the Anthropic adapter where an input_json_delta event arrives without a preceding tool_use content_block_start (malformed SSE, buggy proxy, or mocked stream missing block-start events).

Common situations: Using an Anthropic-compatible gateway/proxy that reorders or drops content_block_start events; unit tests with hand-crafted SSE fixtures missing the tool_use block start; upstream API changes to the streaming event schema.

Related errors

• Error getting prompt: MCP Connection ${serverName} not found
• Error streaming response: ${data.error.message}
• Error streaming response: ${JSON.stringify(data.error)}
• Malformed JSON sent from server: ${json}
• Unsupported tool type in Anthropic: ${tool.type}

AI-assisted analysis of continuedev/continue@5522c6f44c (2026-08-27). Data as JSON: /api/errors/30ee36184310abb3. Report an issue: GitHub.