Undertow MCP: the market liquidity map as agent tools

Endpoint: https://api.seiche.info/undertow/mcp (streamable HTTP, no install)

Your agent knows the price of an asset. This tells it what leaving costs: the per-venue exit cost at your size, how concentrated the depth behind that quote is, and whether depth has actually collapsed lately or only looks calm.

Add it

Claude Code:

claude mcp add --transport http undertow https://api.seiche.info/undertow/mcp

Claude.ai / ChatGPT / Cursor: add a custom connector or MCP server with the URL above. No key and no wallet for the free surface.

Why it exists

On 2026-07-30, selling $1,000,000 of BTC cost 2.87 bp on Binance and 13.65 bp on Bitfinex: about $287 against $1,365 for the same asset in the same minute. Earlier the same morning the dearest venue was a different exchange entirely, at 34.5 bp.

The cheapest door tends to stay put. The worst door changes identity during the day. An agent routing off yesterday's ranking is reading a map that has already moved, and none of this is visible in a price feed.

Tools

Tool	What it serves	Surface
`exit_cost`	Per-venue sell cost in basis points at the nearest published size rung, cheapest and dearest venue with approximate dollar cost, and the venue spread	free
`venue_concentration`	The BTC depth backbone: top venue share of aggregate depth, HHI, effective venue count, per-venue depth in USD	free
`depth_episodes`	Realized depth-collapse episodes with onset, trough, drawdown and recovery, against thresholds declared before any episode accrued	free
`venue_price_reconciliation`	What the price IS when venues disagree: a consensus mark weighted by resting depth over squared half-spread, plus the blindness gap between the deepest venue and consensus	free
`liquidity_tiers`	The board: a liquidity tier per market segment (UST, IG, HY, equities, ETF, FX, China basin, crypto) with the funding-stress overlay	free
`sealed_record`	The sealed forward-calls record, hash-chained and signed before outcomes, misses kept	free
`agent_access_status`	Your tier, today's meter, and how to get more	free
`board_full`	Every measure with its stress percentile or ACCRUING label, limits and analyst note	subscriber
`exit_desk_full`	BTC and ETH at every published rung, plus the venue-failure withdrawal scenario	subscriber

What it refuses to do

It will not flatter you, and an agent quoting it should not either.

PARTIAL is not calm. A segment reads PARTIAL when fewer than two of its measures have earned a scoring history. Four of nine segments read PARTIAL on 2026-07-30, and the board says so instead of guessing.
Exit costs are estimates, interpolated from published quote depth at the 1% and 2% bands. Never a book walk. The snapshot refreshes roughly hourly, so it is a snapshot and not a real-time feed.
Crypto measures are still accruing, so the board has not earned a crypto stress percentile and you should never quote one from it.
The sealed record keeps its misses. Calls are hash-chained and signed before their outcomes are knowable, then scored against the immutable point-in-time board. Quote the misses as prominently as the hits.

Research and market data, not investment advice.

Subscriber tier

Any active subscription unlocks board_full and exit_desk_full. Send /agent to the Telegram bot to mint a bearer token:

{
  "mcpServers": {
    "undertow": {
      "url": "https://api.seiche.info/undertow/mcp",
      "headers": { "Authorization": "Bearer YOUR_TOKEN" }
    }
  }
}

The token proves identity only. Entitlement is re-read from live membership on every call, so access stops when the subscription does rather than when the token expires. Subscriber tools are invisible to an anonymous tools/list, and agent_access_status tells you where you stand.

Only tools/call is metered, reported on X-MCP-Usage-Used, X-MCP-Usage-Limit and X-MCP-Usage-Remaining. GET /undertow/mcp/usage is the self-meter. Hitting a quota returns a normal JSON-RPC result carrying isError and an upgrade pointer, never a dropped connection.

About this repository

This repo is the listing: a README and the two manifests that let directories describe the server accurately. The server itself is hosted at the endpoint above and its engines are a separate, private codebase. Nothing here computes a number.

Siblings from the same lab

Seiche: US money-market funding stress, the plumbing under the markets. Free public good.
LiquiLens: bank, NBFC and lender failure risk, and whether that stress is reaching firms and households.
groundcheck: claim grounding and citation verification for general text.
Palimpsest (https://api.seiche.info/palimpsest/mcp): live internet-censorship signals.

Seiche watches the plumbing, Undertow watches the markets, LiquiLens watches the institutions.

Human front door: liquilens-undertow.com and the Telegram desk.

undertow-mcp

Install to Claude Code

README