# API-existence Oracle: Symbol Exists

> API-existence Oracle: Symbol Exists is a paid API for AI agents from attester.dev, paid per call via x402, $0.005/call, status unknown (last checked 2026-09-16).

Checks whether a named symbol (e.g. function, class, or variable) exists in a given codebase or package registry.

## Facts

- Endpoint: POST https://attester.dev/v1/symbol/exists
- Price: $0.005/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-16
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/api-existence-oracle-symbol-exists-6fb8b751
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap__avJm4fgugaQeWALS0tmN

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 api-existence-oracle-symbol-exists-6fb8b751 -d '<json body>'
```

Example prompt: Can you check whether the symbol `createClient` actually exists and is exported in the `@supabase/supabase-js` package?

## When to prefer this

Use this endpoint when you need to programmatically verify whether a named symbol (function, class, type, variable) is defined and accessible within a package or codebase, especially before generating code that depends on it or before making API calls that reference it. Prefer this over a full package diff endpoint when you only need a targeted existence check rather than change history.

## Known failure modes

- Symbol name or package not provided — returns validation error
- Unknown or misspelled package name — returns not-found or error response
- Symbol exists but is not exported — may return false or qualified result
- Payment not provided or insufficient — returns 402 Payment Required
- Rate limit exceeded — returns 429 or payment error

## How this service works

Deterministic symbol existence for PyPI and npm packages: functions, classes, methods, constants with signatures and deprecation flags, extracted from real artifacts. Negative answers include closest matches and signed proof. $0.005 USDC per check.

## Output

Returns a boolean indicating whether the specified symbol exists, along with any available metadata about the symbol such as its type, export status, or location within the package.

## Request schema (JSON Schema)

```json
{
 "$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": [
      "ecosystem",
      "package",
      "symbol"
     ],
     "properties": {
      "symbol": {
       "type": "string"
      },
      "package": {
       "type": "string"
      },
      "version": {
       "type": [
        "string",
        "null"
       ]
      },
      "ecosystem": {
       "enum": [
        "pypi",
        "npm"
       ],
       "type": "string"
      }
     }
    },
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "POST"
     ],
     "type": "string"
    },
    "bodyType": {
     "enum": [
      "json"
     ],
     "type": "string"
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "example"
   ],
   "properties": {
    "example": {
     "type": "object"
    }
   }
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/api-existence-oracle-symbol-exists-6fb8b751/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from attester.dev](https://www.zero.xyz/host/attester.dev/llms.txt)