How to connect Claude or Codex to Arkham's hosted MCP

You can point Claude, Claude Code, or Codex at Arkham's hosted MCP server and ask about on-chain activity in plain English. The assistant looks up the answer in Arkham. Arkham hosts the server, and the official guide says there is nothing to install.

On October 6, 2026, Arkham's account announced that server for Claude, Claude Code, Codex, or any other MCP-capable tool, and said you can set it up in 1 minute with an Arkham API key. The guide only documents the three named clients, so this walkthrough stops there.

What you need

You need an Arkham API key. The guide says that means an API plan or trial first, then a key created on the API Dashboard. You also need the Claude app (desktop, web, or mobile), Claude Code, or Codex.

The server URL is https://mcp.arkm.com/mcp.

Set up Claude

In the Claude app:

Go to Customize → Connectors and click Add custom connector.
Name it Arkham and paste https://mcp.arkm.com/mcp.
Claude checks the server and shows Couldn't check the server. The guide says this is expected. Click Continue anyway.
Under Authentication, choose No sign-in.
Open Request headers, pick authorization, and enter Bearer YOUR_API_KEY.
Click Add.

The header must be the word Bearer, a space, then your key. Replace YOUR_API_KEY with the key from the dashboard. Do not share that key or paste it into a chat. Anyone with it can use your credits.

The connector is saved to your Claude account, not to one computer. Arkham is then available in every Claude chat on desktop, web, and mobile for that sign-in.

If you do not see Request headers, that option is not available on every Claude plan yet. Use Claude Code or Codex instead. On a Team or Enterprise plan, only a workspace Owner can add the connector. Everyone in the workspace then shares that one API key and its credits.

Set up Claude Code

Run this once in a terminal:

claude mcp add --transport http arkham https://mcp.arkm.com/mcp --header "Authorization: Bearer YOUR_API_KEY" --scope user

Replace YOUR_API_KEY with your real key, and keep the space after Bearer. This is saved on the computer you run it on, for all your projects there. Repeat it on each computer where you use Claude Code.

Set up Codex

The guide's Codex steps are for macOS or Linux. Save the key as an environment variable, then register the server:

export ARKHAM_API_KEY="YOUR_API_KEY"
codex mcp add arkham --url https://mcp.arkm.com/mcp --bearer-token-env-var ARKHAM_API_KEY

ARKHAM_API_KEY must hold the key alone, without Bearer. Add the export line to your shell profile, for example ~/.zshrc, so the key is there next time. Start Codex from a terminal where that variable is already set. Like Claude Code, this is saved on the computer you run it on. The guide does not document a Windows Codex command.

Try a small lookup

Open a new chat and ask one of the guide's sample prompts:

Which chains does Arkham support?
Who are the top 10 counterparties of Binance on Ethereum over the last 7 days?

The guide says the assistant picks the right Arkham lookup and shows the result.

Most lookups use API credits, the same as calling the API directly. A few, such as the list of supported chains, are free. The MCP guide points to Arkham's credit pricing page for the rest; that pricing page was not part of this setup source, so do not assume a lookup is free unless the guide says so.

MCP answers are capped at about 4 MB each. A request that returns more fails, and still uses its credits. Keep MCP requests small.

MCP or the API

Both use the same data, API key, and credits. Pick by the size of the job.

Use MCP for	Use the API for
Questions and quick lookups in a chat	Large exports and backfills
Exploring an address, entity, or token	Paging through thousands of rows
Small result sets, such as a top 10 or the last day	Live streams (WebSocket)
No code	Scripts, apps, and scheduled jobs

Arkham's API guide, labeled v1.1.0 and last updated January 2026, is the companion for that second path. It covers access and onboarding, API keys and authentication, rate limits, credit pricing, pagination, and the data model of addresses, entities, labels, and tags. It is implementation guidance. Endpoint specifications, request and response schemas, and code examples are in the API reference linked from that guide. It is not the MCP connector walkthrough.

If something is not working

Problem	Fix from the guide
Arkham does not show up, or will not connect in Claude or Claude Code	The key header is missing or malformed. It must be `Bearer` with a space, then your key. Check the URL is `https://mcp.arkm.com/mcp`, then restart the app. In Claude Code, run `claude mcp list` to check the connection.
Arkham will not connect in Codex	`ARKHAM_API_KEY` must hold the key alone, without `Bearer`, and be set in the terminal you start Codex from.
An "Attention Required" page appears	The request reached Arkham without a valid key header. Fix the header as above.
Arkham connects, but every question fails with `401` and "Could not verify API Key"	The key itself is wrong. Check it for typos and extra spaces, or create a new one.
"API response exceeds 4 MiB; narrow the query or reduce its limit"	The answer is too large. Ask for less at once, such as a shorter time range or fewer results.
A question times out with `504`	Most lookups have 60 seconds to finish. Ask a narrower question: a shorter time range, one chain, or fewer results.

What to do next

Create or confirm a key on the API Dashboard, add https://mcp.arkm.com/mcp in one of the three clients above, and ask which chains Arkham supports before you try a counterparty lookup. If you need thousands of rows, a backfill, a WebSocket stream, or a scheduled job, leave MCP and use the API guide. If the header and key checks still fail, that guide lists support at api@arkm.com.