Deno "Relative import path not prefixed with / or ./ or ../"

Deno does not resolve bare module specifiers from node_modules by default. An import that is neither a URL, a node:/npm: specifier, nor prefixed with /, ./, or ../ has nowhere to resolve from unless an import map defines it.

What this error means

A run fails with "error: Relative import path \"<name>\" not prefixed with / or ./ or ../ and not in import map". It typically appears when porting Node code that imports packages by bare name.

deno output

error: Relative import path "express" not prefixed with / or ./ or ../
and not in import map from "file:///app/server.ts"
    at file:///app/server.ts:1:21

Common causes

Bare specifier with no import-map entry

Code written for Node uses import express from "express". Deno has no implicit node_modules resolution, so without a map entry the bare name cannot resolve.

Missing npm:/node: prefix

Deno supports npm and Node builtins via explicit npm: and node: prefixes. Omitting the prefix leaves the specifier unresolved.

How to fix it

Use an npm: or node: specifier

Prefix the import so Deno knows where to resolve it.

TypeScript

import express from "npm:express@4";
import { readFile } from "node:fs/promises";

Map the bare name in deno.json

Alternatively, add the bare specifier to the import map so existing imports work unchanged.

deno.json

{
  "imports": {
    "express": "npm:express@4"
  }
}

How to prevent it

Prefix Node/npm imports with npm: / node:, or map them in deno.json.
Commit deno.json so the import map is consistent across runners.
Run deno check in CI to catch unresolved specifiers before deploy.