Newegg PC Builder MCP Skill

Connects Claude to the Newegg PC Builder MCP service. This skill is fully dynamic: it discovers available tools at runtime and lets the LLM decide which tool to call and how to fill its parameters. No tool names or parameter names are hard-coded, so the skill continues to work even after the MCP server updates its API.

MCP Endpoint: https://apis.newegg.com/ex-mcp/endpoint/pcbuilder Script: scripts/mcp_client.py

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Core Workflow (always follow this order)

Step 1 — Discover tools

Always start by listing available tools. Never assume tool names or parameters from previous runs or documentation.

python scripts/mcp_client.py list_tools

The output contains, for each tool:

• name — identifier to use when calling
• description — what it does (may be empty; infer from name + schema)
• inputSchema.properties — available parameters with types and descriptions
• inputSchema.required — mandatory parameters

Step 2 — Select tool and map parameters

Read the list_tools output and decide:

1. Which tool best matches the user's intent?

   • Match on description first; fall back to inferring from name + param names
   • If multiple tools apply, prefer the most specific one
   • If still ambiguous, pick the first one and note the assumption

2. How does user intent map to parameters?

   • Only use parameters present in inputSchema.properties
   • Free-text params (e.g. question, query, text): pass the user's request as a natural-language string describing their need
   • Typed/enum params: map user intent to the closest valid value
   • Leave optional params unset unless you have a clear value
   • Never invent parameters not present in the schema

Step 3 — Call the tool

python scripts/mcp_client.py call <tool_name> '<json_arguments>'

Tool name and arguments are determined at runtime from Step 2. Example:

python scripts/mcp_client.py call v2allin '{"question": "gaming PC RTX 5090 9800X3D best price"}'

Windows PowerShell (important)
PowerShell parses outer double quotes before Python runs. Using \"...\" inside "..." often breaks the JSON string (you may see errors like Got: {\ or “invalid JSON”). Prefer one of:

1. Single-quote the whole JSON (no backslash escapes needed):

   python scripts/mcp_client.py call v2allin '{"question": "gaming PC RTX 3070"}'
   

2. JSON in a file (most reliable for long or nested payloads):

   Set-Content -Path args.json -Encoding utf8 '{"question": "gaming PC RTX 3070"}'
   python scripts/mcp_client.py call v2allin @args.json
   

3. Stdin (pipe or redirect):

   '{"question": "gaming PC RTX 3070"}' | python scripts/mcp_client.py call v2allin -
   

The script supports @path\to\file.json and - for stdin so shells never need to escape inner double quotes.

Where to change things

• Skill + script (recommended): keep examples and mcp_client.py in sync — document PowerShell rules here, and use @file / - in the client to avoid quoting bugs.
• Repo-only docs do not fix agents that load this skill from ~/.agents; updating the skill is the right place for portable behavior.

Step 4 — Interpret the response

Parse the JSON output. Common response shapes:

{ "result": { "summary": "...", "popular": [...], "valued": [...] } }

• summary non-null → use as the primary answer text
• popular / valued arrays present → list the builds
• All result fields null → service returned no data; tell the user and offer to answer from general knowledge instead
• isError: true → report the error and suggest retry

Step 5 — Present results

• Build list: name, total price, key components, brief description
• Compatibility check: clear yes/no with reasoning
• Component details: specs, price, compatibility notes
• No results from API: explain clearly, then offer a manual recommendation

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Edge case handling

Situation	Action
list_tools returns 0 tools	Report service unavailable; answer from training knowledge
Tool description is empty	Infer purpose from name + parameter names
Schema has no required	Treat all params as optional; pass what you have
All response fields null	No data for this query; say so and fall back to general knowledge
HTTP error on list_tools	Report error; do not proceed to call step
HTTP error on call	Retry once; if still failing, fall back to general knowledge
Multiple tools match	Pick most specific; briefly note the choice

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Script reference

scripts/mcp_client.py uses Python standard library only (3.6+, no pip needed). Handles both application/json and text/event-stream responses automatically.

python scripts/mcp_client.py list_tools
    → prints all tools with full parameter schemas

python scripts/mcp_client.py call <tool_name> '<json_args>'
    → calls the tool and prints the JSON response

python scripts/mcp_client.py call <tool_name> @args.json
    → reads JSON arguments from a UTF-8 file (good on Windows)

echo '<json>' | python scripts/mcp_client.py call <tool_name> -
    → reads JSON from stdin

Errors go to stderr with a non-zero exit code. Invalid JSON prints a short hint for PowerShell users.