add-resource

## Context Resources use the `resource()` builder from `@cyanheads/mcp-ts-core`. Each resource lives in `src/mcp-server/resources/definitions/` with a `.resource.ts` suffix. The standard registration pattern uses a `definitions/index.ts` barrel that collects all resources into an `allResourceDefinitions` array for `createApp()`. Fresh scaffolds start with direct imports in `src/index.ts` — the barrel is introduced as definitions grow. Match the pattern already used by the project you're editing. **Tool coverage.** Not all MCP clients expose resources — many are tool-only (Claude Code, Cursor, most chat UIs). Before adding a resource, verify the same data is reachable via the tool surface — either through a dedicated tool, included in another tool's output, or bundled into a broader tool. A resource whose data has no tool path is invisible to a large share of agents. ## Steps 1. **Gather** the resource's URI template, purpose, and data shape from the user's request — ask only if genuinely absent 2. **Design the URI** — use `{paramName}` for path parameters (e.g., `myscheme://{itemId}/data`) 3. **Create the file** at `src/mcp-server/resources/definitions/{{resource-name}}.resource.ts` 4. **Register** the resource in the project's existing `createApp()` resource list (directly in `src/index.ts` for fresh scaffolds, or via a barrel if the repo already has one) 5. **Run `bun run devcheck`** to verify 6. **Smoke-test** with `bun run rebuild && bun run start:stdio` (or `start:http`) ## Template ```typescript /** * @fileoverview {{RESOURCE_DESCRIPTION}} * @module mcp-server/resources/definitions/{{RESOURCE_NAME}} */ import { resource, z } from '@cyanheads/mcp-ts-core'; export const {{RESOURCE_EXPORT}} = resource('{{scheme}}://{{{paramName}}}/data', { description: '{{RESOURCE_DESCRIPTION}}', mimeType: 'application/json', // size: 1024, // optional: content size in bytes, if known params: z.object({ {{paramName}}: z.string().describe('{{PARAM_DESCRIPTION}}'), }), // auth: ['resource:{{resource_name}}:read'], async handler(params, ctx) { ctx.log.debug('Fetching resource', { {{paramName}}: params.{{paramName}} }); // Pure logic — throw on failure, no try/catch return { /* resource data */ }; }, list: async (extra) => ({ resources: [ { uri: '{{scheme}}://all', name: '{{RESOURCE_LIST_NAME}}', mimeType: 'application/json', }, ], }), }); ``` ### With pagination For resources that return large result sets, include `cursor` in the URI template params and use opaque cursor pagination in the `handler`. The cursor arrives as a validated URI param. `paginateArray` requires a `RequestContext` for logging — create one from `requestContextService`: ```typescript import { extractCursor, paginateArray, requestContextService } from '@cyanheads/mcp-ts-core/utils'; // URI template: '{{scheme}}://{{{paramName}}}/items' params: z.object({ {{paramName}}: z.string().describe('{{PARAM_DESCRIPTION}}'), cursor: z.string().optional().describe('Opaque pagination cursor'), }), async handler(params, ctx) { const allItems = await fetchAllItems(params.{{paramName}}); const cursor = extractCursor({ cursor: params.cursor }); const reqCtx = requestContextService.createRequestContext({ operation: 'list-{{paramName}}', parentContext: { requestId: ctx.requestId, traceId: ctx.traceId }, }); const page = paginateArray(allItems, cursor, 20, 100, reqCtx); return { items: page.items, nextCursor: page.nextCursor, }; }, ``` ### Registration ```typescript // src/index.ts (fresh scaffold default) import { createApp } from '@cyanheads/mcp-ts-core'; import { {{RESOURCE_EXPORT}} } from './mcp-server/resources/definitions/{{resource-name}}.resource.js'; await createApp({ tools: [/* existing tools */], resources: [{{RESOURCE_EXPORT}}], prompts: [/* existing prompts */], }); ``` If the repo already uses `src/mcp-server/resources/definitions/index.ts`, add the export to that barrel instead: ```typescript export { {{RESOURCE_EXPORT}} } from './{{resource-name}}.resource.js'; ``` ### Optional: declarative `errors[]` contract Resources can opt into the same typed error contract as tools — bound to a typed `ctx.fail(reason, …)` keyed by the declared reason union: ```typescript import { JsonRpcErrorCode } from '@cyanheads/mcp-ts-core/errors'; export const articleResource = resource('article://{pmid}', { description: 'Read an article by PMID.', errors: [ { reason: 'no_pmid_match', code: JsonRpcErrorCode.NotFound, when: 'PMID not found in the index.', recovery: 'Use pubmed_search_articles to discover valid PMIDs first.' }, { reason: 'withdrawn', code: JsonRpcErrorCode.NotFound, when: 'Article was withdrawn upstream.', recovery: 'Check PubMed directly for retraction or withdrawal notices.' }, { reason: 'upstream_throttled', code: JsonRpcErrorCode.RateLimited, when: 'Upstream PubMed quota hit.', retryable: true, recovery: 'Wait a few seconds and retry the request.' }, ], params: z.object({ pmid: z.string().describe('PubMed ID') }), async handler(params, ctx) { const article = await fetchOne(params.pmid); if (!article) throw ctx.fail('no_pmid_match', `PMID ${params.pmid} not indexed`); if (article.withdrawn) throw ctx.fail('withdrawn'); return article; }, }); ``` Without `errors[]`, the handler receives plain `Context` (no `fail` method) and throws via error factories (`notFound`, `serviceUnavailable`, …) directly. The contract is opt-in. See `skills/api-errors/SKILL.md` for the full pattern, baseline codes, and conformance rules. ### URI template variable completion Add a `complete` map to enable autocompletion for URI template variables. The SDK auto-installs `completion/complete` handling and advertises the `completions` capability when a registered resource template has completion callbacks — no other changes needed. ```typescript import { resource, z } from '@cyanheads/mcp-ts-core'; const ITEM_IDS = ['item-001', 'item-002', 'item-abc']; export const itemResource = resource('items://{itemId}', { description: 'Retrieve an item by ID.', params: z.object({ itemId: z.string().describe('Item identifier') }), handler: (params) => ({ id: params.itemId }), list: () => ({ resources: ITEM_IDS.map((id) => ({ uri: `items://${id}`, name: id })) }), // Per-variable completion callbacks — keys must match URI template variable names. complete: { itemId: async (partial) => ITEM_IDS.filter((id) => id.startsWith(partial)), }, }); ``` Only applies to templated resources (URI templates with `{variable}` syntax). Static URIs don't support completion. ### Other `resource()` options Beyond `description`, `params`, `handler`, and `list`, the builder also supports: | Field | Purpose | |:------|:--------| | `name` | Short human-readable name for `resources/list`. Defaults to a slug derived from the URI template if omitted. | | `output` | Optional Zod schema for runtime validation of the handler return value (parity with `tool()`'s `output`). | | `format` | Optional formatter mapping the handler's return to the `ReadResourceResult.contents[]` shape. Default: string passthrough; objects serialized to JSON. Override when you need to attach permissions, custom encodings, or split into multiple content items. | | `annotations` | Resource annotations (e.g., `audience`, `priority`) — see `ResourceAnnotations`. | | `title` | Human-readable display title (defaults to `name`). | | `examples` | Array of `{ name, uri }` example entries surfaced in `resources/list` for discoverability. | | `complete` | Per-variable completion callbacks for URI template variables. Keys match template variable names. Enables `completion/complete` and the `completions` capability. | ## Checklist - [ ] File created at `src/mcp-server/resources/definitions/{{resource-name}}.resource.ts` - [ ] Resource name passed to `resource()` uses a valid URI template with `{paramName}` syntax - [ ] All Zod `params` fields have `.describe()` annotations - [ ] `output` schema added if the handler returns structured data that benefits from runtime validation - [ ] JSDoc `@fileoverview` and `@module` header present - [ ] `handler(params, ctx)` is pure — throws on failure, no try/catch - [ ] If `errors[]` contract declared: every entry has a `recovery` field (≥5 words, lint-enforced) - [ ] Data is reachable via the tool surface — confirm by checking `src/mcp-server/tools/definitions/` for a tool that exposes this data, or document why this resource is resources-only - [ ] `list()` function provided if the resource is discoverable - [ ] Pagination used for large result sets (`extractCursor`/`paginateArray`) — applies to both `handler` data and `list()` catalogs with many entries - [ ] Registered in the project's existing `createApp()` resource list (directly or via barrel) - [ ] `bun run devcheck` passes - [ ] Smoke-tested with `bun run rebuild && bun run start:stdio` (or `start:http`)