Skip to main content
POST https://api.ethereal.llc/v1/messages/count_tokens
Returns an estimate of how many input tokens a request would cost — handy for cost planning before you actually send it. The request body matches the Anthropic Messages format.
This endpoint is no-auth: it does not require an API key and does not draw down your balance.

​
Headers

HeaderValue
Content-Typeapplication/json

​
Body parameters

​
model
string
required
Model ID: claude-opus-4-8, claude-sonnet-4-6, or claude-haiku-4-5.
​
messages
array
required
A list of messages. Each is { "role": "user" | "assistant", "content": string }.
​
system
string | array
An optional system prompt — a string, or an array of text blocks.

​
Example request

curl https://api.ethereal.llc/v1/messages/count_tokens \
  -H "Content-Type: application/json" \
  -d '{
    "model": "claude-sonnet-4-6",
    "system": "You are a concise assistant.",
    "messages": [
      { "role": "user", "content": "Explain recursion in one sentence." }
    ]
  }'

​
Response

{
  "input_tokens": 28
}
input_tokens is an estimate, not an exact count — use it for cost planning. The actual charge is based on the usage field returned by Messages (Pricing).