From zero to your first call

Choose a route

MCP, the REST API and the SDKs reach every tool. x402 reaches the tools that accept it. MCP and the REST API run the free tools without a key.

• MCPAdd Strale’s MCP server to Claude Desktop, Claude Code, Cursor or any MCP client. The agent searches and calls tools itself.
• REST APIOne endpoint, POST /v1/do, from any language. One API key and one wallet balance cover every tool.
• SDKsTypeScript and Python clients, and packages for LangChain, CrewAI and Composio.
• x402No account and no key. Your agent pays in USDC per request on 275 eligible tools and 89 eligible bundled checks.

Make your first call

The first call runs IBAN Validation, a free tool. The API and MCP calls need no key. Without a key you get 300 free calls a month per IP address, across all free tools. The SDK calls take an API key, and a free tool costs nothing with one.

# Free tool: works without a key, within a monthly allowance. Add your key for more.
curl -X POST https://api.strale.io/v1/do \
  -H 'Content-Type: application/json' \
  -d '{
    "capability_slug": "iban-validate",
    "inputs": {
      "iban": "SE4550000000058398257466"
    },
    "max_price_cents": 5
  }'

{
  "tool": "strale_execute",
  "arguments": {
    "slug": "iban-validate",
    "inputs": {
      "iban": "SE4550000000058398257466"
    },
    "max_price_cents": 5
  }
}

import { Strale } from "straleio";

const strale = new Strale({ apiKey: process.env.STRALE_API_KEY! });
const result = await strale.do({
  capability_slug: "iban-validate",
  inputs: {
    "iban": "SE4550000000058398257466"
  },
  max_price_cents: 5,
});

import os
from straleio import Strale, DoRequest

strale = Strale(api_key=os.environ["STRALE_API_KEY"])
result = strale.do(DoRequest(
    capability_slug="iban-validate",
    inputs={
        "iban": "SE4550000000058398257466",
    },
    max_price_cents=5,
))

{
  "bban": "50000000058398257466",
  "valid": true,
  "bank_code": "500",
  "branch_code": null,
  "check_digits": "45",
  "country_code": "SE",
  "expected_length": 24
}

The output above is the tool’s published example. A live call returns the same fields for your input. More free tools: free tools. For a key, sign up.

Request and response

Every tool runs through POST https://api.strale.io/v1/do. Send a JSON body. With a key, add Authorization: Bearer $STRALE_API_KEY.

A successful call

A success is HTTP 200 with a result and a meta block. Types are shown as words; output is the tool’s own example.

{
  "result": {
    "transaction_id": "string",
    "status": "completed",
    "capability_used": "iban-validate",
    "price_cents": "integer",
    "latency_ms": "integer",
    "wallet_balance_cents": "integer",
    "output": {
      "bban": "50000000058398257466",
      "valid": true,
      "bank_code": "500",
      "branch_code": null,
      "check_digits": "45",
      "country_code": "SE",
      "expected_length": 24
    },
    "provenance": {
      "source": "string",
      "fetched_at": "ISO 8601 timestamp"
    }
  },
  "meta": {
    "audit": {
      "…": "audit record"
    }
  }
}

• price_cents is what this call cost, in euro cents. It is 0 for free tools.
• wallet_balance_cents is your balance after the call. Calls without a key do not carry it; they carry free_tier: true and a usage block with the calls used this month, the monthly limit and when it resets.
• provenance names the source that answered and when it was fetched.
• meta.audit is the audit record for the call.

A failed call

A failure is a non-200 status with error_code, message and, where there is more to say, details. Branch on error_code; the codes are stable.

{
  "error_code": "budget_exceeded",
  "message": "Capability 'address-geocode' costs €0.02 (2 cents) which exceeds your max_price_cents of 1.",
  "details": {
    "capability_slug": "address-geocode",
    "actual_price_cents": 2,
    "max_price_cents": 1
  }
}

Slow tools

Tools that take longer than 10 seconds run in the background. The call returns HTTP 202 with status: "executing", the transaction_id and meta.audit.poll_url. Poll GET /v1/transactions/{transaction_id} until status is completed or failed. The SDKs poll for you.

Handle errors and retries

You are charged when a call succeeds. A call that fails is not charged, and a bundled check that fails in every step is refunded. A bundled check that returns results for some steps is charged in full.

Retry only 429, 500 and 503 responses, and wait a little longer after each: one second, then two, then four. Never retry a 400 without changing the request.

Retry safely and cap spend

Idempotency

Send an Idempotency-Key header on POST /v1/do to make a retry safe. If a call times out on your side, send it again with the same key. Strale returns the first result with meta.idempotency_replay: true and does not run or charge the call twice. Keys work on calls made with an API key, up to 255 characters. Use a new key for a new call, and for a deliberate second attempt after a failure.

curl -X POST https://api.strale.io/v1/do \
  -H "Authorization: Bearer $STRALE_API_KEY" \
  -H "Idempotency-Key: $(uuidgen)" \
  -H 'Content-Type: application/json' \
  -d '{"capability_slug": "iban-validate", "inputs": {"iban":"SE4550000000058398257466"}, "max_price_cents": 1}'

The SDKs take the same value as idempotency_key.

Spend caps

• Per call. max_price_cents is a ceiling on one call. A tool that costs more is refused with budget_exceeded before it runs.
• Per hour. Each account has an hourly spend limit, €100.00 by default. Calls past it are refused with spend_cap_exceeded. To change it, write to [email protected].
• Your balance. Calls are paid from a prepaid wallet. When it is empty, calls are refused with insufficient_balance.
• Preview a price. Add "dry_run": true to see which tool would run and what it costs.

Retrieve a past call

Every call made with an API key has a transaction_id. Fetch the record with it.

curl https://api.strale.io/v1/transactions/$TRANSACTION_ID \
  -H "Authorization: Bearer $STRALE_API_KEY"

const record = await strale.transaction(transactionId);

record = strale.transaction(transaction_id)

{
  "tool": "strale_transaction",
  "arguments": {
    "transaction_id": "<transaction_id>"
  }
}

• The record has the status, the input and output, the price, the latency, the provenance and the audit record.
• Input, output, error and audit content are cleared 90 days after the call. The record of the call itself stays.
• GET /v1/transactions lists your most recent calls.
• Calls made without a key can be looked up by anyone with the ID, with the content left out.
• x402 responses carry no transaction ID. The payment details are in _meta.payment of the response.

API reference

The full machine-readable reference is the OpenAPI document at https://api.strale.io/openapi.json. Send Accept: text/markdown for a readable version. It also lists the x402 endpoints.

• GET https://api.strale.io/v1/capabilities lists every tool with its inputs, outputs and price.
• Each tool page shows the inputs, output fields, price and limits for one tool.
• GET https://api.strale.io/v1/wallet/balance returns your balance in euro cents.