Anthropic API / Anthropic API

Anthropic SDK MCP connector intermittently emits tool_use instead of mcp_tool_use

Debug why Anthropic SDK with MCP beta returns plain tool_use instead of expected mcp_tool_use, causing agent loops to hang Includes evidence for Anthropic API troubleshooting demand.

Source-backed Last updated May 23, 2026 1 source Needs local verification

Category: Anthropic API
Error signature: MCP connector model intermittently emits tool_use instead of mcp_tool_use for tools declared in mcp_toolset — conversation stalls on client side
Quick fix: Compare the failing environment with a known working setup, then change one configuration value at a time.
Updated: May 23, 2026
Verification status: Source-backed
Evidence: 1 public source URL

Before you change production

This page includes public source URLs in the imported troubleshooting record. Compare those references with your version and environment before applying changes.

Reproduce the smallest failing action and save non-secret logs before changing configuration.
Check versions for Anthropic API, related SDKs, package managers, CI runners, and hosting providers.
Change one setting or dependency at a time, then rerun the same failing command or request.
Avoid destructive commands, credential rotation, billing changes, or security relaxations without a rollback plan.

What this error means

MCP connector model intermittently emits tool_use instead of mcp_tool_use for tools declared in mcp_toolset — conversation stalls on client side is a Anthropic API failure pattern reported for developers trying to debug why anthropic sdk with mcp beta returns plain tool_use instead of expected mcp_tool_use, causing agent loops to hang. Based on the imported evidence, treat this as a tool-specific troubleshooting page rather than a generic API error.

Why this happens

GitHub Issue anthropics/anthropic-sdk-python#1581 (open, created 2026-05-21, 1 comment, 2605 related MCP/Auth issues in claude-code repo). Affects claude-sonnet-4-6 and other 4.x models under streaming API. Intermittent bug with multi-turn agentic loops mixing local function tools + mcp_toolset. This causes API billing charges for failed turns plus developer time wasted debugging. Category mapping: Anthropic SDK/MCP errors → Anthropic API per SKILL.md category table.

Common causes

GitHub Issue anthropics/anthropic-sdk-python#1581 (open, created 2026-05-21, 1 comment, 2605 related MCP/Auth issues in claude-code repo). Affects claude-sonnet-4-6 and other 4.x models under streaming API. Intermittent bug with multi-turn agentic loops mixing local function tools + mcp_toolset. This causes API billing charges for failed turns plus developer time wasted debugging. Category mapping: Anthropic SDK/MCP errors → Anthropic API per SKILL.md category table.

Quick fixes

Confirm the exact error signature matches MCP connector model intermittently emits tool_use instead of mcp_tool_use for tools declared in mcp_toolset — conversation stalls on client side.
Check the Anthropic API account, local tool state, and provider configuration involved in the failing workflow.
Compare the failing environment with a known working setup, then change one configuration value at a time.

Platform/tool-specific checks

Verify the command, editor, extension, or API client that produced the error.
Compare local settings with CI, deployment, or editor-level settings when the error appears in only one environment.
Avoid deleting credentials, local model data, or project settings until the failing scope is clear.

Step-by-step troubleshooting

Capture the exact error message and the command, editor action, or request that triggered it.
Check whether the failure is account/auth, quota/rate, model/provider, local runtime, or deployment configuration.
Review the source evidence below and compare it with your environment.
Apply one change at a time and rerun the smallest failing action.
Keep the working fix documented for the team or deployment environment.

How to prevent it

Keep provider/tool configuration documented.
Record non-secret diagnostics such as tool version, provider name, model name, and command path.
Add a lightweight check before CI or production workflows depend on the tool.

Diagnostic flow for this page

Match MCP connector model intermittently emits tool_use instead of mcp_tool_use for tools declared in mcp_toolset — conversation stalls on client side exactly before applying the quick fix.
Compare the failing environment with Anthropic API versions, account scope, provider settings, and deployment context.
Check the listed common causes in order, starting with the cause that best matches your logs.
Use the evidence status below to decide whether to confirm against public sources or official documentation.
Apply one reversible change, rerun the smallest failing action, and keep rollback notes.

FAQ

What does MCP connector model intermittently emits tool_use instead of mcp_tool_use for tools declared in mcp_toolset — conversation stalls on client side mean in Anthropic API?

MCP connector model intermittently emits tool_use instead of mcp_tool_use for tools declared in mcp_toolset — conversation stalls on client side indicates the workflow described by "Anthropic SDK MCP connector intermittently emits tool_use instead of mcp_tool_use" failed in a Anthropic API context. Start by confirming the exact signature and the component that emitted it.

What should I check first for MCP connector model intermittently emits tool_use instead of mcp_tool_use for tools declared in mcp_toolset — conversation stalls on client side?

Check whether this cause matches your environment: GitHub Issue anthropics/anthropic-sdk-python#1581 (open, created 2026-05-21, 1 comment, 2605 related MCP/Auth issues in claude-code repo). Affects claude-sonnet-4-6 and other 4.x models under streaming API. Intermittent bug with multi-turn agentic loops mixing local function tools + mcp_toolset. This causes API billing charges for failed turns plus developer time wasted debugging. Category mapping: Anthropic SDK/MCP errors → Anthropic API per SKILL.md category table.

Is the MCP connector model intermittently emits tool_use instead of mcp_tool_use for tools declared in mcp_toolset — conversation stalls on client side guidance source-backed?

The "Anthropic SDK MCP connector intermittently emits tool_use instead of mcp_tool_use" page is labeled source-backed. It has 1 public source URL from github.com, so use that evidence status when deciding how much additional verification you need.

When should I avoid the quick fix for MCP connector model intermittently emits tool_use instead of mcp_tool_use for tools declared in mcp_toolset — conversation stalls on client side?

For "Anthropic SDK MCP connector intermittently emits tool_use instead of mcp_tool_use", avoid applying "Compare the failing environment with a known working setup, then change one configuration value at a time." when the error text differs, the affected version or provider is different, or the change would touch credentials, billing, DNS, production deploy settings, or irreversible data.

What should I collect before debugging MCP connector model intermittently emits tool_use instead of mcp_tool_use for tools declared in mcp_toolset — conversation stalls on client side?

For "Anthropic SDK MCP connector intermittently emits tool_use instead of mcp_tool_use", collect the failing Anthropic API command or request, non-secret configuration, versions, timestamps, request IDs when available, and the smallest reproduction that still triggers the signature.