Nansen x402 API by Nansen

# Fix list: Nansen x402 API

From Anchor Terminal's listing at https://www.anchorterminal.com/tools/nansen-x402-api, the October 2026 research run, assessed 1 October 2026. Grade B, 67.4 out of 100.

This is everything the published grade says the listing lacks, the biggest possible gain to the total first. It comes from the reason given for each score, the checklist each category was scored against (https://www.anchorterminal.com/benchmark/#checklist), the provenance checks, the deductions, what we couldn't check and what the review panel asked for. A fix counts at the next check, once it's public.

For a coding agent working on Nansen x402 API: work through the items below in the product, its docs and its public pages. Each category gives the reason for its score, with the points each checklist item earned, and the checklist itself, so the gap is the items that earned less than their points. Change the product, not the wording, and keep a note of what you changed and where it's published.

## 1. Reliability, 45 out of 100, up to 11 more on the total

Why it scored 45: We found no status page. status.nansen.ai doesn't resolve, and neither the API docs nor the site footer links one (0). No readable incident history (5). Limits published, 15 a second and 300 a minute on Free, 75 and 1,500 on paid plans, and 5 a second and 60 a minute per wallet on x402 (15). 429 carries `Retry-After` and a `retry_after` field plus `X-Nansen-RateLimit-Scope`, timeouts and upstream errors say to retry with backoff, and x402 calls that hit the rate limit aren't charged. Every call is a read (15). No SLA found (0). We found no beta or preview label on the x402 route (10).

The checklist (https://www.anchorterminal.com/benchmark/#checklist-reliability):

Hosted APIs, MCP servers, models and platforms.

- 20, a public status page with component history (Statuspage, Instatus, BetterStack or the vendor's own).
- 0 to 30, the incident record for the last 90 days on that page. 30 for a clean record or trivial incidents only, 20 for minor incidents only, 10 for one major outage (an hour or more of a core API down, or errors across the board), 0 for several. 5 when there's no history we could read, and the note says so.
- 15, rate limits documented with numbers.
- 15, documented 429 or overload handling (Retry-After, backoff guidance), and idempotency keys or safe-retry guidance where writes are involved.
- 10, an SLA published for any paid tier.
- 10, the surface agents use is generally available, not beta or preview.

Local packages, SDKs, frameworks and stdio MCP servers.

- 20, installs from an official package with supported runtimes stated.
- 25, a public CI and test suite, passing on the default branch.
- 0 to 25, open crash or regression issues relative to activity (25 for few and handled, 0 for many, old and unanswered).
- 15, semver discipline and breaking changes called out in a changelog.
- 15, version 1.0 or later, or declared stable.

Protocols are read from their reference implementations, the public facilitators or servers, spec stability and test vectors.

## 2. Security & auth, 45 out of 100, up to 9.6 more on the total

Why it scored 45: The x402 route needs no credential, so nothing leaks beyond the paying wallet. The keyed API uses one account key with no scopes we could find (15). Read-only data, and each x402 call costs a fixed $0.01 or $0.05 (15). Responses include token names and symbols that their creators set, alongside Nansen's own labels, with no injection guidance (7). Credit cost comes back in response headers and each x402 payment is on chain (8). We found no security page, disclosure policy or certification in the docs or on nansen.ai (0).

The checklist (https://www.anchorterminal.com/benchmark/#checklist-security):

- 0 to 30, the credential model. 30 for OAuth 2.1 with scopes, or scoped and revocable keys with rotation. 20 for plain revocable API keys. 10 for one all-powerful key. 10 off when a secret can travel in a URL query string as a documented option.
- 0 to 20, read-only or least-privilege modes, and confirmation or approval for destructive actions.
- 0 to 15, prompt-injection posture where the tool returns untrusted content (documented mitigations or guidance). A tool that returns no untrusted content gets 10.
- 0 to 15, audit logs or per-call visibility for the operator.
- 0 to 20, a security programme. security.txt or a disclosure policy, a bug bounty, SOC 2 or ISO 27001, advisories handled in public.

Models are read for retention, whether API data trains models (and whether that's off by default), zero-retention options and certifications. Frameworks for telemetry defaults, approval hooks, guardrails and sandboxing.

## 3. Transparency & trust, 51 out of 100, up to 4.3 more on the total

Why it scored 51: Closed service with published terms (updated 10 August 2026), API terms and a master services agreement (15). The privacy policy says API usage patterns, query parameters, IP addresses and timestamps are collected but gives no retention period and names no legal entity (12). Deprecations come with dates. The `address` to `wallet_address` rename on 24 September 2026 keeps the old field working until at least 23 December 2026 and flags it with a `Warning: 299` header (18). Service providers are named by category only, and Singapore is the one location named (6).

The checklist (https://www.anchorterminal.com/benchmark/#checklist-transparency):

- 0 to 30, source availability and licence clarity. 30 for open source under an OSI licence, 15 for closed with clear terms, 0 for unclear terms.
- 0 to 30, data handling and retention statements that agree with each other (privacy policy, DPA, retention periods, subprocessors).
- 0 to 20, a deprecation policy or notices with dates.
- 0 to 20, telemetry disclosed with an opt-out (local software), or subprocessors and data locations disclosed (hosted).

The other half of Transparency and trust is the provenance score, computed from checked facts (below). The category score is the mean of the two.

## 4. Schema & documentation, 84 out of 100, up to 2.6 more on the total

Why it scored 84: Each endpoint page embeds an OpenAPI 3.1 definition. We found no single downloadable spec (22). llms.txt at docs.nansen.ai, Markdown copies of every page and a `?ask=` query on the docs (10). Endpoint pages describe what each returns, but not when to prefer one endpoint over a similar one (12). Typed inputs with a chain enum, `buy_or_sell` enum, sortable-field lists, `per_page` from 1 to 1,000 and required fields marked (14). An error catalogue with stable codes, `request_id`, `doc_url` and `param`. The `who-bought-sold` page has no worked request or response example (11). Dated changelog with one page per change (15).

The checklist (https://www.anchorterminal.com/benchmark/#checklist-schema):

APIs and MCP servers.

- 25, a machine-readable contract (a public OpenAPI file or similar; for MCP, typed JSON Schema inputs on every tool).
- 10, llms.txt or Markdown docs served for agents.
- 0 to 20, descriptions that say what a tool is for, when to use it and when not to, read from the tool definitions in the source or the API reference.
- 0 to 15, typed inputs with enums, constraints and required fields, and no free-form JSON blobs.
- 0 to 15, examples and documented error responses.
- 15, versioning and a public changelog.

Models are read from the API reference, the OpenAPI file, llms.txt, the structured-output and tool-use docs and the model cards. Frameworks from docs a model can follow, typed interfaces, examples and the API reference.

## 5. Agent ergonomics, 86 out of 100, up to 2.3 more on the total

Why it scored 86: Pagination defaults to 10 rows (`per_page` up to 1,000) and filters on labels, volumes and dates keep responses small (20). `page`, `per_page`, `order_by` and range filters on the endpoints we read (20). Errors carry a stable `code`, the field at fault and a docs link, and the docs tell clients to fall back on the HTTP status for codes they don't know (20). All x402 endpoints are reads sent as POST, failed and rate-limited calls aren't charged, and there are no idempotency keys (18). Three required fields on `who-bought-sold` (chain, token address, date range). We found a Nansen MCP server and CLI but didn't verify SDKs in two languages (8).

The checklist (https://www.anchorterminal.com/benchmark/#checklist-ergonomics):

- 0 to 25, context cost. For MCP, the number and size of the tool definitions (25 for ten or fewer compact tools, 15 for 11 to 30, 5 for more than 30, plus up to 10 back for toolsets, dynamic loading or read-only subsets). For APIs, whether responses can be sized (field selection, limits, summaries).
- 20, pagination, filtering and output-size controls.
- 20, actionable, documented error responses, codes and messages an agent can recover from.
- 20, idempotency or safe retries, and for MCP the `readOnlyHint` and `destructiveHint` annotations.
- 15, sensible defaults, few required parameters, and official SDKs in at least two languages.

Models are read for tool use, structured output, prompt caching, context length, batch and SDKs. Frameworks for how much code and how many defaults a tool-calling agent with MCP needs.

## 6. Maintenance & community, 75 out of 100, up to 2.2 more on the total

Why it scored 75: Changelog entry on 24 September 2026 (30). Seven dated entries since 17 July (20). Public changelog and docs that answer questions through `?ask=`. We didn't test support (10). An MCP server with connectors for Claude, ChatGPT and Grok is documented. We didn't verify official SDKs (10). No public package to check (5).

The checklist (https://www.anchorterminal.com/benchmark/#checklist-maintenance):

- 0 to 30, time since the last release, or the last published model or API change for a closed service. 30 within 30 days, 20 within 90, 10 within 180, 0 older.
- 20, at least three releases or dated changelog entries in the last 90 days.
- 0 to 25, responsiveness. Issues and pull requests answered on GitHub (the open issues and how recent the replies are). For closed services, a public changelog and a support or community channel that answers, 0 to 15.
- 15, presence in the official MCP registry under a verified namespace (MCP servers), or current official SDKs (APIs and models).
- 10, package health, current dependencies and CI.

Models are read for deprecation notice periods and model churn rather than release counts.

## 7. Payments & pricing, 95 out of 100, up to 0.6 more on the total

Why it scored 95: x402 on Nansen's own api.nansen.ai for every Pro endpoint except labels, 17 at $0.01 and 8 named Premium and Smart Money endpoints at $0.05, in USDC on Base, Solana or Monad. Labels are excluded, and the 200 to 750-credit agent endpoints don't appear in the x402 tiers (35). Per-call prices published without login (20). Free plan with 100 trial credits and a daily top-up to 10, with no payment required (20). The docs call x402 "fully permissionless", a wallet with USDC is enough (20).

The checklist (https://www.anchorterminal.com/benchmark/#checklist-payments):

The published rubric, also on the [x402 page](https://www.anchorterminal.com/x402/).

- 40, a machine payment protocol (x402, MPP or L402) on the tool's own endpoints. 10 to 30 when it covers only some endpoints or only goes through a third party, and the note says which.
- 20, per-call or per-unit pricing published without a login. 10 for public plan-only pricing, 0 for "contact sales" or prices behind a login.
- 20, a free tier or trial that doesn't need a card.
- 20, autonomous onboarding, meaning an agent can get access without a person signing up in a browser (keyless use, x402, a programmatic key API).

Payment platforms and agent wallets rarely charge for their own API over a machine protocol, so the first line has steps for them, and the highest one that applies counts. 40 when x402, MPP or L402 runs on all their own endpoints, 30 when it runs on part of their own API, 25 when their merchants can accept one, 20 for running a facilitator, 15 for paying as a buyer, and 0 when the only protocol is their own. Merchant acceptance sits above a facilitator because the platform's own customers can charge agents through it, while a facilitator settles for sellers who wire up the protocol themselves. The counter-argument (a facilitator does more for the protocol as a whole) has a point. Each note says which step applied.

Open-source software you run yourself is scored on its hosted or paid option if it has one. A free, self-hosted package with nothing to buy gets 20, 20 and 20 for the last three lines, and 0 to 40 for the first only if it ships a payment protocol.

## What we couldn't check

What we couldn't read counted as absent. Publishing it on a page a plain HTTP fetch can read (not only in a browser) lets the next check count it.

- unchecked: whether Nansen runs a status page under another address, since status.nansen.ai doesn't resolve and neither docs nor site link one
- unchecked: whether keyed API keys can be scoped, rotated or revoked
- The Smart Money tier lists a `/api/v1/smart-money/*` wildcard, so the exact count of $0.05 endpoints is uncertain
- The listing has no provenance block. The site footer names only "Nansen", legal documents are at nansen.ai/legal and the changelog is docs.nansen.ai/api/changelog

## Weaknesses

- No status page, incident history or SLA that we could find
- No security policy, disclosure route or certification found
- Privacy policy gives no retention period and names no legal entity
- x402 is limited to 60 calls a minute per wallet
- Labels aren't sold by x402, and the agent endpoints don't appear in its tiers

## What costs an agent a turn today

The notes we give agents before they call it. Each one is a workaround an agent shouldn't need.

- Check the price tier before calling. Premium and Smart Money endpoints cost $0.05, five times the Basic ones
- Send `wallet_address`, not `address`, on pnl-summary, related-wallets and defi-holdings. The old name is deprecated
- Set `per_page` and a date range. Defaults are page 1 with 10 rows, and the maximum is 1,000
- On 429, wait the `Retry-After` seconds. The call isn't charged
- Pass `chain` explicitly. It's a required enum on the token endpoints

## What the review panel asked for

- one downloadable OpenAPI file
- worked who-bought-sold example
- publish a security policy
- state data retention

## When it's done

Send what changed and where it's published as a dispute (https://www.anchorterminal.com/builders/#disputes, or `POST https://www.anchorterminal.com/api/v1/contact` with `"kind": "dispute"`). Disputes are answered in public, and the listing is checked again by the same checklist. Paying for an audit or a listing claim changes nothing here.