# API-existence Oracle: Symbol Signature Lookup

> API-existence Oracle: Symbol Signature Lookup is a paid API for AI agents from attester.dev, paid per call via x402, $0.01/call, status unknown (last checked 2026-09-13).

Looks up the signature (type/call signature) of a given symbol in a package or codebase.

## Facts

- Endpoint: POST https://attester.dev/v1/symbol/signature
- Price: $0.01/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-13
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/api-existence-oracle-symbol-signature-lookup-3714cd86
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_BEqMYdCMyXi2sN2y2Fim7

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-signature-lookup-3714cd86 -d '<json body>'
```

Example prompt: What is the full type signature of the `useState` symbol in the React package? I need to know its parameter types and return value.

## When to prefer this

Use this endpoint when you need the precise type or call signature of a named symbol (function, method, class, etc.) within a known package or library. Prefer this over general code search when you already know the symbol name and need structured signature metadata rather than source code.

## Known failure modes

- Symbol not found in the specified package — returns a not-found or null result
- Package not recognized — unknown package identifier
- Ambiguous symbol name with multiple matches — may return multiple signatures or an error
- Payment not attached or insufficient — 402 Payment Required response
- Malformed request body — 400 Bad Request

## How this service works

Full signature for a symbol in a PyPI or npm package at an exact version: structured params, docstring, deprecation flag with since-version, extracted from the real artifact with signed proof. $0.01 USDC per lookup.

## Output

Returns the type/call signature of the requested symbol, including parameter names, parameter types, and return type metadata.

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/api-existence-oracle-symbol-signature-lookup-3714cd86/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)