Build mcp use client

Build mcp-use Client

Build or audit deterministic TypeScript MCP client code using the mcp-use SDK: MCPClient, MCPSession, mcp-use/browser, mcp-use/react (useMcp, McpClientProvider, useMcpClient, useMcpServer), code mode, and the npx mcp-use client CLI.

The client is the half that connects to an MCP server, lists/calls tools, reads resources, manages sessions, and handles auth — without an LLM choosing what to call.

When to use this skill

Use this skill when any of these are true:

• the user imports from "mcp-use", "mcp-use/browser", or "mcp-use/react"
• the code constructs new MCPClient(...), calls createSession()/createAllSessions(), or uses client.close()/closeAllSessions()
• a React app uses useMcp, McpClientProvider, useMcpClient, or useMcpServer (note: state not status; storageProvider not persistenceProvider)
• the project runs npx mcp-use client or has mcp.json, mcp.config.json, or .vscode/mcp.json config files
• the work is connecting to existing MCP servers, listing tools/resources/prompts, calling them deterministically, or wiring up auth/sampling/elicitation callbacks on the client side
• the request involves code mode via executeCode()/search_tools() from a client
• the task is fixing client-side issues: 404 session recovery, idle proxy timeouts, dropped reconnects, OAuth re-auth loops, or React StrictMode duplicate sessions

Do NOT use this skill if:

• an LLM picks and orchestrates tools via MCPAgent — route to build-mcp-use-agent
• the work imports from "mcp-use/server", defines server.tool/server.resource/server.prompt, or builds widgets/transports/server auth — route to build-mcp-use-server
• the code imports directly from @modelcontextprotocol/sdk without the mcp-use wrapper — route to build-mcp-server-sdk-v1 or build-mcp-server-sdk-v2
• the only goal is headless CLI verification of an already-running MCP server with mcpc — route to test-by-mcpc-cli

Inspect the path the user named directly. Do not start with a repo-wide scan when a subdirectory is given.

Non-Negotiable Rules

These rules are load-bearing — violating them is the most common source of client bugs.

#	Rule	Why
1	Import from mcp-use, mcp-use/browser, or mcp-use/react only	Hand-rolling raw @modelcontextprotocol/sdk calls inside a wrapper-library project re-implements features and breaks reconnection/auth integration
2	await createSession() / createAllSessions() before use	Sessions are async; using an unresolved promise yields runtime errors that look like config bugs
3	Always cleanup: closeAllSessions() for normal clients; client.close() for code mode	Code mode allocates external executors (VM/E2B) that leak without close()
4	Discover before hardcoding: list tools/resources/prompts before assuming names	Server schemas drift; hardcoded names break silently when the server adds optional args
5	Handle CallToolResult.isError, content, structuredContent, and _meta deliberately	The shape is union-like; assuming content[0].text exists masks real tool errors
6	Set timeout, maxTotalTimeout, and AbortSignal for long-running tools	Defaults will hang on slow tools; production work needs explicit cancellation
7	Tokens belong server-side or in OAuth flows; browser headers carry only public values	mcp-use/browser headers are visible to anyone who opens devtools
8	Use mcp.state (not status) and storageProvider (not persistenceProvider)	These names changed; older docs and AI-generated code still ship the old ones
9	Check optional capabilities (e.g. completion) before calling them	Servers advertise capabilities — calling unsupported ones throws confusing errors
10	Report what validation actually ran; do not imply runtime coverage from tsc alone	Type checks are necessary but not sufficient for client behavior verification

Workflow

1. Detect what exists

Inspect the target path and look for client-side signals:

tree -L 3 2>/dev/null || find . -maxdepth 3 -type f | sort

Confirm:

• package.json has "mcp-use" as a dependency
• imports from "mcp-use", "mcp-use/browser", or "mcp-use/react"
• presence of MCPClient, MCPSession, useMcp, McpClientProvider, useMcpClient, useMcpServer
• npx mcp-use client scripts, mcp.json, mcp.config.*, .vscode/mcp.json
• direct imports from @modelcontextprotocol/sdk — these route to raw SDK skills, not here
• imports from "mcp-use/server" — these route to build-mcp-use-server
• MCPAgent usage — that routes to build-mcp-use-agent

Run the version preflight when Node/npm are available:

bash skills/build-mcp-use-client/skills/build-mcp-use-client/scripts/check-mcp-use-version.sh <target-path>

Read scripts/check-mcp-use-version.sh.md before changing the script or interpreting non-obvious output.

2A. Existing client found — audit then fix

Run the diagnostic script first:

bash skills/build-mcp-use-client/skills/build-mcp-use-client/scripts/diagnose-client.sh <target-path>

Read scripts/diagnose-client.sh.md for the diagnostic categories and exit-code contract.

Audit the implementation against the surface map below before editing. Apply focused fixes — do not rebuild a working client from scratch.

Audit surface	Read	Check for
constructor, config files, sessions, imports	references/guides/client-configuration.md, references/guides/environments.md	correct entry point, current Node/package baseline, awaited session creation, cleanup
tools, resources, prompts, completion	references/guides/tools.md, references/guides/resources.md, references/guides/prompts.md, references/guides/completion.md	discovery before calls, isError handling, structuredContent, pagination, capability checks, timeouts/abort
callbacks, auth, notifications	references/guides/sampling.md, references/guides/elicitation.md, references/guides/authentication.md, references/guides/notifications-and-logging.md	callback names, browser secret boundary, token expiry/re-auth, list-changed handlers
React	references/guides/usemcp-and-react.md	state not status, one provider for multi-server apps, StrictMode-safe addServer, cleanup, all states handled
code mode	references/guides/code-mode.md	executor isolation, executeCode(), search_tools(), client.close()
production hardening	references/patterns/production-patterns.md, references/patterns/anti-patterns.md, references/troubleshooting/common-errors.md	reconnection, 404 recovery, idle proxy timeout, process shutdown, dropped connections

2B. No client found — build the smallest working integration

If repo context already gives the environment, server target, and auth shape, skip the questionnaire and build directly.

Pick the server target before coding:

• Existing MCP server in the repo: connect to it and discover real capabilities.
• Client mechanics only, no domain server: use @modelcontextprotocol/server-everything for a smoke test.
• Domain-specific tool required but no server exists: route to build-mcp-use-server first.

If context is missing, ask only the questions you cannot answer:

1. Environment — Node CLI, Node service, browser app, React app, or npx mcp-use client.
2. Server count — one server or multiple.
3. Transport — stdio, Streamable HTTP, or mixed.
4. Auth — none, bearer token, OAuth, or custom public headers.
5. React shape — standalone useMcp or provider-based multi-server app.
6. Callbacks — sampling, elicitation, notifications/logging, or none.
7. Code mode — no, trusted-local VM, E2B, or custom isolation.
8. Production hardening — basic cleanup, reconnect/health checks, or full setup.

3. Build or fix in this order

1. Align prerequisites against current npm view mcp-use metadata; do not keep old Node 18 guidance for current releases.
2. Use the right import path: mcp-use for Node, mcp-use/browser for browser, mcp-use/react for React.
3. Configure real server IDs and discover capabilities before hardcoding tool/resource/prompt names.
4. Add auth without printing or committing secrets.
5. Add timeouts, abort handling, cleanup, and reconnection before calling the work production-ready.
6. Validate with type/lint/tests and, when possible, a real connect/list/call/read smoke test.

Core Surface Map

Route to the reference file matching the user's intent. Do not load files speculatively.

Trigger	File	Why
install, first Node/browser/React/CLI client	references/guides/quick-start.md	minimal runnable paths and first calls
choose Node/browser/React/CLI entry point	references/guides/environments.md	environment matrix, imports, limits
configure MCPClient, config files, sessions	references/guides/client-configuration.md	constructor shape, callbacks, 404 recovery
manage multiple servers dynamically	references/guides/server-manager.md	server manager and dynamic config patterns
list/call tools, set timeouts, abort	references/guides/tools.md	result handling, progress, cancellation
read resources, templates, subscriptions	references/guides/resources.md	pagination, content shapes, notifications
list/get prompts	references/guides/prompts.md	prompt arguments and prompt updates
implement argument/resource completion	references/guides/completion.md	capability checks and debounce guidance
handle sampling requests	references/guides/sampling.md	onSampling, model preferences, React callbacks
handle elicitation requests	references/guides/elicitation.md	onElicitation, helpers, form and URL modes
handle auth, re-auth, browser secrets	references/guides/authentication.md	OAuth, bearer tokens, headers, CLI auth, DCR/manual registration
receive list-changed events, roots, logs	references/guides/notifications-and-logging.md	notification listeners and logging callbacks
build React clients	references/guides/usemcp-and-react.md	hook/provider props, lifecycle, states, reconnection
use code mode	references/guides/code-mode.md	executors, imports, safety, browser/React limits
use npx mcp-use client	references/guides/cli-reference.md	CLI commands, sessions, JSON scripting
copy complete examples	references/examples/client-recipes.md	Node, browser, React, code mode recipes
scaffold project layouts	references/examples/project-templates.md	package structures and starter files
harden production behavior	references/patterns/production-patterns.md	shutdown, retries, reconnect, observability
review mistakes before finalizing	references/patterns/anti-patterns.md	known bad patterns and fixes
diagnose specific errors	references/troubleshooting/common-errors.md	connection, auth, React, code mode, import failures
verify package baseline	scripts/check-mcp-use-version.sh	Node/package/npm drift diagnostics
diagnose a stuck client	scripts/diagnose-client.sh	config/import/auth/lifecycle scan

Decision Rules

Runtime and version

• Treat npm view mcp-use version engines peerDependencies --json as the source of truth for current install guidance.
• Run scripts/check-mcp-use-version.sh before copying examples into a project.
• Prefer examples that use the major/minor line npm metadata confirms. Avoid stale ^1.21.0 style pins.

React

• Use one McpClientProvider for multi-server apps.
• Make dynamic addServer() calls inside useEffect idempotent under StrictMode; clean up temporary servers with removeServer() when appropriate.
• Gate UI and effects on every state: discovering, authenticating, pending_auth, ready, failed.
• Resource-reading effects must avoid setting state after unmount or after a newer request supersedes the old one.

Code mode

• VM executor for trusted local code only.
• E2B or custom isolation for untrusted or multi-tenant code.
• Always call client.close() because code mode may allocate external resources.

Streaming and reconnection

• Prefer Streamable HTTP for new HTTP clients; legacy SSE only for compatibility.
• Do not build WebSocket clients for MCP — mcp-use does not target WebSocket transport.
• Route long-running tools through timeout/progress/abort guidance in references/guides/tools.md and reconnection guidance in references/patterns/production-patterns.md.

Validation

Use the smallest honest set:

npm run typecheck
npm run lint
npm test
npx tsx src/client.ts
npx mcp-use client connect --stdio "npx -y @modelcontextprotocol/server-everything" --name smoke

For React, exercise every rendered state: discovering, authenticating, pending_auth, ready, failed. For auth issues, test 401/403, expired refresh token, popup blocked, redirect callback failure, and pending_auth loops against references/guides/authentication.md plus references/troubleshooting/common-errors.md.

Output Contract

When finishing a client task, report:

1. Target path and environment: Node, browser, React, or CLI.
2. Servers discovered or configured.
3. Key APIs used: MCPClient, MCPSession, useMcp, provider hooks, code mode, CLI.
4. Validation commands actually run.
5. Whether runtime behavior was exercised or only type/lint passed.
6. References consulted.
7. Auth/secrets caveat — without printing the secret values.