Unit Converter API

Convert between units -- length, weight, temperature, volume, speed, data storage. Formula included. Pay-per-call via x402 (USDC on Base L2) -- no API key, no signup, no rate-limit wall.

Part of the klymax402 marketplace -- 100 x402 micropayment APIs for AI agents, one wallet, USDC on Base.

Quickstart -- MCP

Add to your MCP client config (Claude Desktop, Cursor, ElizaOS, etc.):

config.json

{
  "mcpServers": {
    "unit-converter": {
      "url": "https://unit-converter.api.klymax402.com/mcp"
    }
  }
}

Quickstart -- HTTP (x402)

Terminal

curl -X POST "https://unit-converter.api.klymax402.com/api/convert" \
  -H "Content-Type: application/json" \
  -d '{"value":"1","from":"...","to":"..."}'
# -> 402 Payment Required, with an x402 payment challenge in the response body

Any x402-aware client (@x402/fetch, x402-agent-tools, ATXP) handles the 402 -> sign -> retry cycle automatically.

Tools

Tool	Method	Path	Price	Description
`utility_convert_units`	POST	`/api/convert`	$0.003	Convert a value between measurement units

`utility_convert_units`

Use this when you need to convert between measurement units. Returns the conversion result with formula in JSON.

Parameters

Name	Type	Required	Description
`value`	number	yes	The numeric value to convert
`from`	string	yes	Source unit (e.g. km, lb, celsius, l, mph, MB)
`to`	string	yes	Target unit (e.g. mi, kg, fahrenheit, gal, km/h, GB)
`category`	string	no	Optional category hint: length, weight, temperature, volume, speed, data

Example response:

config.json

{"inputValue":100,"from":"km","to":"mi","result":62.1371,"formula":"100 km * 0.621371 = 62.1371 mi","category":"length"}

When to use: unit conversions in calculations, data analysis, scientific computing, recipe scaling, and engineering applications.

Not for: currency conversion (use finance_convert_currency), timezone conversion (use utility_convert_timezone), stock prices (use finance_get_stock_price).

Example agent prompts

"Convert between measurement units"

Payment

Protocol: x402 -- HTTP-native pay-per-call, no signup, no API key
Network: Base L2 (eip155:8453)
Asset: USDC
Facilitator: Coinbase CDP (primary), PayAI (fallback)
Also reachable via ATXP (OAuth-wrapped x402, RFC 9728 protected-resource metadata)

Part of klymax402

100 x402 micropayment APIs for AI agents -- one wallet, USDC on Base, zero signup.

Catalog: https://klymax402.com/llms.txt
Full API reference: https://klymax402.com/llms-full.txt
Live stats: https://klymax402.com/stats

License

MIT