# SignalHarness Prompt Token Budget Estimator

> SignalHarness Prompt Token Budget Estimator is a paid API for AI agents from signalharness.ai, paid per call via x402, $0.005/call, status unknown (last checked 2026-09-15).

Estimates the token budget required for a given prompt or request JSON, helping agents plan LLM cost and capacity before execution.

## Facts

- Endpoint: POST https://signalharness.ai/api/agent/services/prompt_token_budget_estimate/invoke
- Price: $0.005/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/signalharness-prompt-token-budget-estimator-612adb31
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_J-jZHhFoJi2N-yYHw2O0N

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 signalharness-prompt-token-budget-estimator-612adb31 -d '<json body>'
```

Example prompt: Before I send this API request payload to the language model, can you estimate the token budget it will need? Here's the request JSON: {"model":"gpt-4","messages":[{"role":"user","content":"Summarize the quarterly earnings report for Apple Inc."}]}

## When to prefer this

Choose this endpoint when you need a lightweight, pay-per-call token budget estimate before committing to a full LLM API call — especially useful in cost-sensitive agent pipelines, batch processing workflows, or when validating that prompts stay within model context limits. Prefer this over client-side tokenizer libraries when you want a verifiable, receipted estimate with an audit trail on Base.

## Known failure modes

- Invalid or malformed request_json string returns a validation error
- request_json exceeding 65536 characters is rejected
- Missing required request_json field causes a 400-level error
- Ambiguous or empty JSON objects may trigger warnings in the analysis
- Payment failure or insufficient USDC balance prevents execution

## How this service works

Explore 330 pay-per-call x402 API services and 27 agent-native digital products, with Base USDC pricing, secure Polar checkout, and free discovery.

## Output

Returns a JSON object containing an analysis_json field with the token budget estimate, a warnings array for data quality notices, the service_id, evidence_scope indicating the data came from caller-supplied input, and a full execution receipt with payment metadata, latency, and a result SHA256 hash for verification.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "request_json": {
   "type": "string",
   "maxLength": 65536,
   "minLength": 2
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "replay": false,
  "result": {
   "warnings": [
    "Verify the caller-supplied data before relying on this result."
   ],
   "service_id": "prompt_token_budget_estimate",
   "analysis_json": "{\"example\":\"schema-valid caller-supplied data\"}",
   "evidence_scope": "caller_supplied_data"
  },
  "status": "succeeded",
  "receipt": {
   "asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
   "usage": [],
   "status": "succeeded",
   "network": "eip155:8453",
   "artifacts": [],
   "endedAtMs": 0,
   "latencyMs": 0,
   "paymentId": "example-payment",
   "receiptId": "example-receipt",
   "requestId": "example-request",
   "serviceId": "prompt_token_budget_estimate",
   "executionId": "example-execution",
   "startedAtMs": 0,
   "amountAtomic": "5000",
   "resultSha256": "d2f74257ed217974638a0b50508a760084b29338c2a851d7940ef1cd67e37f85",
   "serviceVersion": "1.0.0",
   "settlementReference": "0x0000000000000000000000000000000000000000000000000000000000000000"
  },
  "artifacts": [],
  "requestId": "example-request",
  "executionId": "example-execution"
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/signalharness-prompt-token-budget-estimator-612adb31/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from signalharness.ai](https://www.zero.xyz/host/signalharness.ai/llms.txt)