# Task Checkpoint Evidence

> Task Checkpoint Evidence is a paid API for AI agents from phion.systems, paid per call via x402, $0.003/call, status unknown (last checked 2026-10-20).

Binds task state, sequence number, and checkpoint hash into a signed cryptographic evidence record for AI agent task integrity

## Facts

- Endpoint: POST https://phion.systems/v1/paid/trust/task-checkpoint-evidence?utm_source=zero.xyz
- Price: $0.003/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-20
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/task-checkpoint-evidence-af6e7d2d
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_11kqClyyQKs--elGfUIHD

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 task-checkpoint-evidence-af6e7d2d -d '<json body>'
```

Example prompt: Create a signed checkpoint evidence record binding the current task state 'payment_confirmed', sequence number 3, and checkpoint hash 'sha256:abc123...' so I have a tamper-evident audit record for this agent task.

## When to prefer this

Choose this endpoint when you need a cryptographically signed, tamper-evident record binding a specific task state and sequence to a checkpoint hash — particularly for multi-step agentic workflows where you need audit trails, dispute-resolution evidence, or integrity guarantees at discrete task phases. Prefer this over generic logging when non-repudiability and signed provenance are required.

## Known failure modes

- Invalid or missing task state returns 400 error
- Malformed checkpoint hash causes binding failure
- Sequence number out of expected order may be rejected
- Payment failure via x402 prevents evidence generation
- Signature generation failure if signing infrastructure is unavailable

## How this service works

Bind task state, sequence and checkpoint hash in signed evidence

## Output

A signed evidence record cryptographically binding the task state, sequence number, and checkpoint hash. The receipt serves as a tamper-evident attestation that can be used for audit trails, dispute resolution, or integrity verification of an AI agent's task progression.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input",
  "output"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "body"
   ],
   "properties": {
    "body": {
     "type": "object",
     "additionalProperties": true
    }
   }
  },
  "output": {
   "type": "object",
   "required": [
    "example"
   ],
   "properties": {
    "example": {
     "type": "object",
     "additionalProperties": true
    }
   }
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json"
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/task-checkpoint-evidence-af6e7d2d/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from phion.systems](https://www.zero.xyz/host/phion.systems/llms.txt)