ProvenPin Install

mime-types lookup: working versions (tested 2026-10-16)

Look up content-type from an extension and extension from a type with mime-types, asserting json, html, png and wasm plus the charset helper and graceful unknown handling, offline.

passed5 passed · 0 failed2026-10-16 15:20 UTC
Status
passed
Last passed
2026-10-16 15:20 UTC
Tests
5 / 5
Language
TypeScript
Runtime
node v22.23.3
pinned versions3
mime-types@3.0.2@types/node@26.6.5tsx@4.23.15
run it
npm install --no-audit --no-fund --ignore-scripts=false
npm test
test environment
node v22.23.3
linux 6.17.0-1022-azure
x64
runner: github-actions 38923127324

The code

Exactly the files that passed. Your agent can pull them with get_recipe("mime-types-lookup") (install), or see them on GitHub.

package.json
{
  "name": "mime-types-lookup",
  "private": true,
  "type": "module",
  "scripts": {
    "test": "node --import tsx --test test/*.test.ts"
  },
  "dependencies": {
    "mime-types": "3.0.2"
  },
  "devDependencies": {
    "@types/node": "26.6.5",
    "tsx": "4.23.15"
  }
}
src/mime.ts
import mime from "mime-types";

export function typeFromExtension(extension: string): string | undefined {
  const type = mime.lookup(extension);
  return type === false ? undefined : type;
}

export function extensionFromType(type: string): string | undefined {
  const extension = mime.extension(type);
  return extension === false ? undefined : extension;
}

export function contentTypeFor(extension: string): string | undefined {
  const type = mime.contentType(extension);
  return type === false ? undefined : type;
}

export function charsetFor(type: string): string | undefined {
  const charset = mime.charset(type);
  return charset === false ? undefined : charset;
}
test/mime.test.ts
import { test } from "node:test";
import assert from "node:assert/strict";
import {
  charsetFor,
  contentTypeFor,
  extensionFromType,
  typeFromExtension,
} from "../src/mime.ts";

test("resolves content-type from common extensions", () => {
  assert.equal(typeFromExtension("json"), "application/json");
  assert.equal(typeFromExtension(".json"), "application/json");
  assert.equal(typeFromExtension("html"), "text/html");
  assert.equal(typeFromExtension(".png"), "image/png");
  assert.equal(typeFromExtension("wasm"), "application/wasm");
});

test("resolves extension from common types", () => {
  assert.equal(extensionFromType("application/json"), "json");
  assert.equal(extensionFromType("text/html"), "html");
  assert.equal(extensionFromType("image/png"), "png");
  assert.equal(extensionFromType("application/wasm"), "wasm");
});

test("builds a full content-type with charset", () => {
  assert.equal(contentTypeFor("json"), "application/json; charset=utf-8");
  assert.equal(contentTypeFor("html"), "text/html; charset=utf-8");
  assert.equal(charsetFor("text/html"), "UTF-8");
  assert.equal(charsetFor("application/json"), "UTF-8");
});

test("handles unknown input gracefully", () => {
  assert.equal(typeFromExtension("not-a-real-ext-xyz"), undefined);
  assert.equal(extensionFromType("application/x-not-a-real-type"), undefined);
  assert.equal(contentTypeFor("not-a-real-ext-xyz"), undefined);
  assert.equal(charsetFor("application/wasm"), undefined);
});

test("round trips a lookup back to its extension", () => {
  const type = typeFromExtension("wasm");
  assert.equal(type, "application/wasm");
  assert.equal(extensionFromType(type as string), "wasm");
});

Connect to ProvenPin

Add the free MCP server so your agent can pull this recipe and others like it. Same setup as the docs.

terminal
claude mcp add --transport http provenpin https://mcp.provenpin.com/mcp

Any other MCP client: Streamable HTTP at https://mcp.provenpin.com/mcp. No API key, no signup.