# Best x402 debugging and monitoring tools (2026)

Canonical: https://x402.chikocorp.com/blog/best-x402-debugging-monitoring-tools-2026.html

There are now enough x402 checkers that choosing one is a real decision. This page compares the ones
that actually inspect an endpoint — not the ones that only list resources — on four questions: what
does it verify, can you call it free, can an agent call it without a browser, and where does it stop.

Disclosure: we build one of these (x402 Preflight). It is listed with the same criteria as the rest,
including the part it does not do.

## At a glance

| Tool | What it checks | Free tier | Agent-callable |
|---|---|---|---|
| x402 Preflight (https://x402.chikocorp.com/verify) | Live 402 challenge, price/network/asset/payTo consistency, Bazaar metadata, CORS, cache, redirects, OpenAPI and llms.txt discovery | Yes, inspection free and unlimited | Yes: JSON API + MCP server (3 tools) |
| x402lint (https://x402lint.com/) | Validation of x402 v1/v2 config shapes and the Bazaar extension; CLI, npm library, Claude skill | Yes | Partly: npm/CLI/skill, no hosted API |
| tx402 tools (https://tools.tx402.io/) | 402 inspector, challenge verification, spend-policy playground, price history, endpoint compare, failed-payment replay | Yes | Yes: JSON and markdown per page |
| Settlens (https://settlens.com/product) | Deterministic check catalog across assess, CI gate, monitor, evidence; signed SARIF reports | Platform, not primary | Yes: CLI, GitHub Action, container, HTTP API, MCP |
| x402scan (https://www.x402scan.com/) | Discovery and indexing: who sells what, at what price, transaction volume | Yes | Browsing; not a checker |
| Agentic Market validator (https://agentic.market/validate) | Endpoint validation against marketplace expectations | Yes | Web form |
| Apify x402 endpoint checker (https://apify.com/ttimesai/x402-endpoint-checker) | Probes without paying, validates v1/v2 challenges, optional comparison against the Bazaar listing, batch mode | Apify credits | Yes, as an Apify actor |

## How to choose

- **"I just deployed and nothing sells."** A challenge reader first (Preflight's verifier or tx402's inspector). One request eliminates half the causes.
- **"My config looks wrong in code."** x402lint validates the object before it ships.
- **"It works for me but buyers say it is broken."** The buyer's view: challenge consistency against the listing, discovery metadata, CORS.
- **"I need this every deploy."** Settlens (CI + signed evidence) or any monitor product. A one-off check nobody reruns is how endpoints rot.
- **"I want to know who sells what."** x402scan indexes; it does not diagnose.

## What a checker can and cannot prove

A read-only check proves the endpoint answers with a parseable challenge, that amount/network/asset/
receiver are internally consistent, that discovery metadata does not contradict the live challenge,
and that the HTTP surface behaves as a buyer requires.

It does **not** prove that a payment settles, that the facilitator accepts the signature, or that the
resource is delivered. Those need a funded wallet and a real transaction.

## What separates a good check from a pretty one

1. **Evidence, not just a verdict.** "BLOCK, score 16" is useless without the status code and the header that was missing.
2. **It distinguishes a defect from a policy decision.** A price above *your* ceiling is your policy, not the seller's bug.
3. **The agent that pays can call it.** If the only interface is a web page, an autonomous buyer cannot use it.

## Try it

```sh
curl -s -X POST https://x402.chikocorp.com/api/preflight/inspect \
  -H 'content-type: application/json' \
  -d '{"resource_url":"https://your-api.example.com/paid/route","method":"GET","max_price_usd":1}'
```

Related: https://x402.chikocorp.com/blog/x402-bazaar-listing-not-working.html ·
https://x402.chikocorp.com/blog/x402-bazaar-census-26692-endpoints.html