# Physics Constants Lookup by Key, Symbol, or Name

> Physics Constants Lookup by Key, Symbol, or Name is a paid API for AI agents from physics.openverbs.com, paid per call via x402, $0.004/call, status unknown (last checked 2026-09-14).

Looks up a single CODATA 2018 physical constant by its key, symbol, or exact name, returning its value, unit, uncertainty, and category.

## Facts

- Endpoint: POST https://physics.openverbs.com/v1/constant
- Price: $0.004/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-14
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/physics-constants-lookup-by-key-symbol-or-name-b412a2ff
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_zy4IDEzmGL2BCMdMoTOc4

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability physics-constants-lookup-by-key-symbol-or-name-b412a2ff -d '<json body>'
```

Example prompt: What is the CODATA 2018 recommended value, unit, and uncertainty for Planck's constant? Look it up by its symbol 'h'.

## When to prefer this

Use this endpoint when you need an exact, authoritative lookup of a single physical constant by a known identifier (key, symbol, or full name) and want the CODATA 2018 recommended value with uncertainty. Prefer this over the search endpoint when you already know the identifier precisely and want a direct, deterministic result rather than a ranked list of candidates.

## Known failure modes

- Query does not match any known constant key, symbol, or name — returns empty or not-found response
- Ambiguous query matches multiple constants — may return best single match or an error
- Input string exceeds 60 characters — rejected by schema validation
- Payment not fulfilled via x402 protocol — request blocked before processing

## How this service works

Look up a physical constant by its key (e.g. "speed-of-light"), symbol (e.g. "c") or exact name. Returns the CODATA 2018 recommended value, unit, relative standard uncertainty (0 for values that are exact by SI definition) and category.

## Output

Returns the CODATA 2018 recommended value of the matched physical constant, along with its SI unit string, relative standard uncertainty (0 for exact SI-defined values), and a category label (e.g. universal, atomic, electromagnetic).

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method",
    "bodyType",
    "body"
   ],
   "properties": {
    "body": {
     "type": "object",
     "required": [
      "query"
     ],
     "properties": {
      "query": {
       "type": "string",
       "maxLength": 60,
       "minLength": 1,
       "description": "Constant key, symbol or exact name."
      }
     },
     "additionalProperties": false
    },
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "POST"
     ],
     "type": "string"
    },
    "bodyType": {
     "enum": [
      "json",
      "form-data",
      "text"
     ],
     "type": "string"
    }
   },
   "additionalProperties": false
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/physics-constants-lookup-by-key-symbol-or-name-b412a2ff/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from physics.openverbs.com](https://www.zero.xyz/host/physics.openverbs.com/llms.txt)