Invalid API Key

What the error looks like

# Python SDK
anthropic.AuthenticationError: Error code: 401 - {
  "type": "error",
  "error": {
    "type": "authentication_error",
    "message": "invalid x-api-key"
  }
}

# If key is missing entirely:
anthropic.AuthenticationError: Error code: 401 - {
  "error": {
    "type": "authentication_error",
    "message": "x-api-key is required"
  }
}

# TypeScript SDK
APIError [AuthenticationError]: 401 invalid x-api-key

Step 1 — Get a valid API key

1. Go to console.anthropic.com → Settings → API Keys
2. Click Create Key and give it a descriptive name
3. Copy the key immediately — Anthropic shows it only once
4. The key starts with sk-ant- (e.g., sk-ant-api03-eyJ...)

If you lost an existing key, you must revoke it and create a new one.

Step 2 — Set the environment variable correctly

# Terminal (Linux/Mac) — for current session only
export ANTHROPIC_API_KEY="sk-ant-api03-your-key-here"

# Terminal (Windows PowerShell)
$env:ANTHROPIC_API_KEY = "sk-ant-api03-your-key-here"

# Permanently (Linux/Mac) — add to ~/.bashrc or ~/.zshrc
echo 'export ANTHROPIC_API_KEY="sk-ant-api03-your-key-here"' >> ~/.zshrc
source ~/.zshrc

# Verify it's set
echo $ANTHROPIC_API_KEY

Common mistakes:

• Including quotes in the value: ANTHROPIC_API_KEY="sk-ant-..." — the quotes should only be in the shell command, not stored as part of the value
• Spaces around the =: ANTHROPIC_API_KEY = sk-ant-... — no spaces allowed in shell assignment
• Setting it in a different terminal tab than where you run the script

Step 3 — Using .env files (Python)

# .env file (in project root, never commit to git)
ANTHROPIC_API_KEY=sk-ant-api03-your-key-here

# ⚠️ No quotes around the value in .env files
# ⚠️ Add .env to .gitignore immediately

# your Python script
from dotenv import load_dotenv  # pip install python-dotenv
import os
import anthropic

load_dotenv()  # MUST call this before creating the client

api_key = os.getenv("ANTHROPIC_API_KEY")
if not api_key:
    raise ValueError("ANTHROPIC_API_KEY not found in environment")

client = anthropic.Anthropic(api_key=api_key)

# Or let the SDK pick it up automatically after load_dotenv():
client = anthropic.Anthropic()  # reads ANTHROPIC_API_KEY automatically

Step 4 — Using .env files (Node.js / TypeScript)

# Install dotenv
npm install dotenv

# .env file
ANTHROPIC_API_KEY=sk-ant-api03-your-key-here

// your script.js — add this FIRST
require("dotenv").config();  // CommonJS
// OR
import "dotenv/config";      // ESM

import Anthropic from "@anthropic-ai/sdk";

const client = new Anthropic(); // reads process.env.ANTHROPIC_API_KEY

// Or pass explicitly:
const client = new Anthropic({
  apiKey: process.env.ANTHROPIC_API_KEY,
});

Verify your key with curl (fastest debug)

# Test your key directly — bypasses all SDK complexity
curl -s https://api.anthropic.com/v1/models \
  -H "x-api-key: $ANTHROPIC_API_KEY" \
  -H "anthropic-version: 2023-06-01" | jq .

# If valid: {"data": [...list of models...]}
# If invalid: {"type":"error","error":{"type":"authentication_error","message":"invalid x-api-key"}}

Deploy environments (Vercel, Railway, Render, etc.)

Environment variables set in your local shell are not available in deployed apps. Set them in the platform's dashboard:

• Vercel: Project Settings → Environment Variables → add ANTHROPIC_API_KEY
• Railway: Project → Variables → add key
• Render: Service → Environment → add key
• Heroku: heroku config:set ANTHROPIC_API_KEY=sk-ant-...
• GitHub Actions: Settings → Secrets → Actions → New repository secret
• AWS Lambda: Configuration → Environment variables → edit

Diagnostic checklist

# Python — check if key is visible to your script
import os
key = os.getenv("ANTHROPIC_API_KEY", "NOT FOUND")
print(f"Key starts with: {key[:10]}...")  # should be "sk-ant-api"
print(f"Key length: {len(key)}")           # should be ~100+ chars

# Check for invisible whitespace corruption
print(repr(key[:20]))  # should NOT show \n, \t, or spaces