wsdot-mcp-server: Instructions file for Claude Code

Developer Protocol

Server: @cyanheads/wsdot-mcp-server Version: 0.2.5 Framework: @cyanheads/mcp-ts-core ^0.12.3 Engines: Bun ≥1.3.0, Node ≥24.0.0 MCP SDK: @modelcontextprotocol/server ^2.0.0 (protocol revisions 2026-07-28 and 2025-*) Zod: ^4.4.3

Read the framework docs first: node_modules/@cyanheads/mcp-ts-core/CLAUDE.md contains the full API reference — builders, Context, error codes, exports, patterns. This file covers server-specific conventions only.

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Core Rules

• Logic throws, framework catches. Tool/resource handlers are pure — throw on failure, no try/catch. Plain Error is fine; the framework catches, classifies, and formats. Use error factories (notFound(), validationError(), etc.) when the error code matters.
• Use ctx.log for request-scoped logging. No console calls.
• Use ctx.state for tenant-scoped storage. Never access persistence directly.
• Need input the caller didn't supply? return ctx.requestInput(...) and read ctx.inputs when the handler is re-entered. Never await for user input mid-handler.
• Secrets in env vars only — never hardcoded.
• Close the loop on issues. When implementing work tracked by a GitHub issue, comment on the issue with what landed and close it. Do both — a comment without a close leaves stale issues open; a close without a comment leaves no record of what shipped. The comment is for future readers — state the concrete changes, not the conversation that produced them.

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Patterns

Tool

import { tool, z } from '@cyanheads/mcp-ts-core';
import { getTrafficApiService } from '@/services/traffic/traffic-service.js';

export const getMountainPasses = tool('wsdot_get_mountain_passes', {
  description: 'Returns current road conditions for all Washington State mountain passes.',
  annotations: { readOnlyHint: true },
  input: z.object({}),
  output: z.object({
    passes: z.array(z.object({
      passName: z.string().optional().describe('Name of the mountain pass.'),
      roadCondition: z.string().optional().describe('Current road condition.'),
    })).describe('Current conditions for all WA mountain passes.'),
  }),

  async handler(input, ctx) {
    const svc = getTrafficApiService();
    const passes = await svc.getMountainPassConditions();
    ctx.log.info('Mountain passes fetched', { count: passes.length });
    return { passes };
  },

  // format() populates content[] — the markdown twin of structuredContent.
  // Different clients read different surfaces (Claude Code → structuredContent,
  // Claude Desktop → content[]); both must carry the same data.
  // Enforced at lint time: every field in `output` must appear in the rendered text.
  format: (result) => [{
    type: 'text',
    text: result.passes.map(p => `**${p.passName}**: ${p.roadCondition}`).join('\n'),
  }],
});