Simple Hypothesis MCP

Build a minimal MCP server for the Hypothesis web annotation API (https://web.hypothes.is/).

Goal

A stdio MCP server in TypeScript that lets Claude Code agents read and write Hypothesis annotations, focused on reading group annotations to drive code/doc updates.

Tech stack

• TypeScript (strict)
• @modelcontextprotocol/sdk (stdio server)
• Native fetch (Node 18+)
• Vitest for unit tests
• ESLint with typescript-eslint (strictTypeChecked)
• eslint-plugin-unicorn (selective rules)
• Prettier for formatting
• lint-staged + simple-git-hooks for commit hygiene
• No frameworks — stdio only

Auth

Read HYPOTHESIS_API_TOKEN from 1Password (MCP configuration should use 1Password CLI) with its reference: op://Private/Hypothesis-API/credential. Base URL is https://hypothes.is/api.

Tools to implement

1. get_groups — GET /api/profile/groups Returns user’s group memberships (id, name, public id).

2. search_annotations — GET /api/search Params: group? (pubid), uri?, text?, user?, tag?, limit? (default 50, max 200), offset? Returns: array of annotations with id, uri, text, tags, user, created, updated, target (includes quote/selector).

3. get_annotation — GET /api/annotations/:id Returns full annotation detail.

4. get_group_annotations — POST /api/bulk/annotation Fetches all annotations for a group efficiently. Params: group (pubid), limit? (default 200). Use the bulk endpoint for large datasets.

5. create_annotation — POST /api/annotations Params: uri (required), text (required), group? (pubid, defaults to “world” i.e. public), tags? (string[]) Minimal payload — no need to handle target selectors for now.

6. update_annotation — PATCH /api/annotations/:id Params: id (required), text?, tags?

Annotation shape to expose (normalized, drop noise)

interface Annotation {
  id: string
  uri: string          // page URL annotated
  text: string         // annotation body
  tags: string[]
  user: string         // acct:username@hypothes.is
  group: string        // group pubid
  created: string      // ISO
  updated: string      // ISO
  quote?: string       // selected text (from target[0].selector, TextQuoteSelector)
}

TypeScript config

Strict mode plus these additional flags:

{
  "noUncheckedIndexedAccess": true,
  "exactOptionalPropertyTypes": true,
  "noImplicitOverride": true
}

target ES2022, module NodeNext, outDir dist.

ESLint config

• Use typescript-eslint flat config with strictTypeChecked ruleset
• parserOptions.project pointing at tsconfig.json
• Add eslint-plugin-unicorn with these rules enabled selectively:
  • unicorn/prefer-node-protocol (enforce node: imports)
  • unicorn/no-nested-ternary
  • unicorn/prefer-module
  • unicorn/throw-new-error
• Run ESLint and Prettier as separate concerns (do NOT use eslint-plugin-prettier)

Prettier config

{
  "singleQuote": true,
  "semi": false,
  "trailingComma": "all"
}

Git hooks (simple-git-hooks + lint-staged)

On pre-commit: run prettier --write then eslint --fix on staged .ts files only.

package.json

"simple-git-hooks": {
  "pre-commit": "npx lint-staged"
},
"lint-staged": {
  "*.ts": ["prettier --write", "eslint --fix"]
}

Run npx simple-git-hooks after install to register the hook.

Error handling

• Throw descriptive errors on non-2xx responses, include status + body
• Validate required params and throw before making the request
• No unhandled promise rejections — ESLint’s strictTypeChecked will enforce this

Project structure

tools/mcp/hypothesis/
  src/
  index.ts        # MCP server setup and tool registration
  client.ts       # Hypothesis API client (typed fetch wrapper)
  types.ts        # Shared types
  tests/
  client.test.ts  # Vitest unit tests for API client
  tools.test.ts   # Vitest unit tests for tool input validation and response mapping
  package.json
  tsconfig.json
  .eslintrc.js (or eslint.config.js for flat config)
  .prettierrc
  vitest.config.ts
  README.md

package.json requirements

• "type": "module"
• Scripts:
  • build: tsc
  • start: node dist/index.js
  • test: vitest run
  • test:watch: vitest
  • lint: eslint src tests
  • format: prettier --write src tests
  • typecheck: tsc --noEmit
• bin entry so it can be run directly after build

Tests to write (Vitest)

• Mock fetch using vi.stubGlobal — do not make real HTTP calls
• client.test.ts:
  • Each API method constructs the correct URL and headers
  • Non-2xx responses throw with status and body included in message
  • quote is correctly extracted from TextQuoteSelector in target selectors
  • Missing required params throw before fetch is called
• tools.test.ts:
  • search_annotations default limit is applied when omitted
  • get_group_annotations uses the bulk endpoint
  • create_annotation defaults group to __world__ when omitted

Constraints

• No class-based architecture — plain functions only
• Keep src under 300 lines total
• No express or any HTTP server — stdio only
• All node: built-in imports must use the node: protocol prefix
• No any types — ESLint strictTypeChecked will flag them

README should include

• Install, build, and test steps
• How to get a Hypothesis API token (https://hypothes.is/account/developer)
• Claude Code MCP config snippet:

{
  "mcpServers": {
    "hypothesis": {
      "type": "stdio",
      "command": "node",
      "args": ["/absolute/path/to/hypothesis-mcp/dist/index.js"],
      "env": {
        "HYPOTHESIS_API_TOKEN": "$(op read 'op://Private/Hypothesis-API/credential')"
      }
    }
  }
}

Deliverable

Working, buildable, tested code. After writing all files:

1. Run npm install
2. Run npx simple-git-hooks to register git hooks
3. Run npm run build — must compile with zero errors
4. Run npm run lint — must pass with zero errors
5. Run npm test — all tests must pass

Fix any type, lint, or test errors before finishing.