For agents

One call per place. Sized for your context. Guide: /llms.txt

line ≈321 tokens, 7 forecastsMET Norway alone 20,159 tokens, 1 forecast

Measured on a fixed NYC example; the live body below can differ.

curl · line

curl "https://groundhog.markets/api/v1/blend?place=new-york-city"

curl · week

curl "https://groundhog.markets/api/v1/blend?place=new-york-city&size=week"

Claude Code

claude mcp add --transport http groundhog https://groundhog.markets/mcp

Cursor · mcp.json

{
  "mcpServers": {
    "groundhog": {
      "url": "https://groundhog.markets/mcp"
    }
  }
}

200 · text/markdown · 570 B · live NYC body

New York City, NY, US (KNYC), Wed 2026-10-28 (tomorrow): high 62.0°F, low 46.0°F; median of 9 forecasts, 5 model groups; highs 60.0–62.4. Rain <2% (n 4: ENS, GEFS, GEPS members' share, raw; NBM calibrated <2%), 0.00 in. Now 52°F at KNYC 01:51Z (maint). Alerts: none. As of 02:03Z. Page: https://groundhog.markets/p/new-york-city. Credits: NOAA/NWS (public domain); MET Norway, DWD, GEFS via dynamical.org, GeoNames (CC BY 4.0); ECCC (Open Licence); based on ECMWF data (CC BY 4.0; ECMWF accepts no liability); modified by groundhog. Full: groundhog.markets/credits

Other clients

Client	Setup
Claude Desktop, claude.ai	Settings → Connectors → Add custom connector → https://groundhog.markets/mcp
VS Code · .vscode/mcp.json	`{"servers":{"groundhog":{"type":"http","url":"https://groundhog.markets/mcp"}}}`
Windsurf · mcp_config.json	`{"mcpServers":{"groundhog":{"serverUrl":"https://groundhog.markets/mcp"}}}`
Any MCP client	Streamable HTTP: POST JSON-RPC 2.0 to https://groundhog.markets/mcp, no session. No key.

Sizes

size	What	Bytes	Tokens	JSON tokens
line	One day: median high and low, n, groups, highs range, rain, now, alerts, compact credits	616 B	≈321	≈761
week	One row per day: median, ranges, n, rain, plus alerts and compact credits	936 B	≈566	≈1,931
table	Each source per day, then median, ranges, n, rain, now, alerts, full credits	2.9 KB	≈1,567	≈6,954
series	72 h every 3 h: a fixed source set, ENS p10/p90, median, n, full credits	2.8 KB	≈1,564	≈2,175
metno	MET Norway alone: its JSON for 1 place, 1 forecast	39.4 KB	20,159 (measured)	—
raw	Every source yourself: 391 requests, 11 hosts	90.9 MB	—	—

Bytes and tokens of the New York City example bodies. Tokens: Claude Opus 5.5 count_tokens. line and week carry one compact credit line; table and series the full lines.

Endpoints

Method	Path	Returns
GET	/api/v1/blend	The blend at a size (main call)
GET	/api/v1/blend?variable=rain	Rain: members' share of 0.01 in or more and heavier, amounts by source, so far today, month to date
GET	/api/v1/blend?size=runs	Trading fields: each source's newest runs by day, run_utc, fetched_at; NBM XND, P12, Q12
GET	/api/v1/nbm?stn=	NBM text columns of one run + the day view
GET	/api/v1/history	As-issued history: daily, nbm, obs; run, lead, asof (no look-ahead)
GET	/api/v1/history/files	Bulk history files, gzip TSV per day and month
GET	/api/v1/places?q=	Find a place: slug, name, tier, stations
GET	/api/v1/sources	Sources: group, licence, runs, status, credit
GET	/api/v1/status	Freshness per source, jobs, version
GET	/api/v1/markets?place=	Weather markets: station, rule, so far, ours, result. No prices
GET	/api/v1/receipts	Our settle value vs the venue's result, last 30 days
GET	/api/v1/schema.json	JSON Schema of every JSON body
GET	/api/v1	Every endpoint, one line each
GET	/openapi.json	OpenAPI 3.1
GET	/mcp/server-card	MCP server card
GET	/credits	Every full credit line, text/plain
POST	/mcp	MCP, stateless JSON-RPC 2.0
GET	/llms.txt	Agent guide, under 5 KB
GET	/llms-full.txt	The guide plus params, fields, examples, errors
GET	/p/new-york-city.md	A place page as Markdown
GET	/agents.md, /sources.md, /about.md	These pages as Markdown
GET	/health	{"ok":true}, no auth

Params

Param	Values	Default
place	slug · name · City, ST · ICAO · lat,lon; repeat up to 10× (line, week)	required
date	today · tomorrow · +N (%2BN or N in a URL) · YYYY-MM-DD	today before 15:00 local, else tomorrow
days	1–7	line 1 · week, table 7
size	line · week · table · series · runs	line
format	md · tsv · json	line md, else tsv
units	F · C	°F in the US, else °C
hours, step	24–168 · 1, 3, 6 (series)	72 · 3
include_6h	0 · 1 (alias alt)	0: 6‑hourly max/min left out while ≥ 4 others remain
all	0 · 1 (table)	0; 1 adds twin and stale rows
credits	compact · full · short	line, week compact; else full
runs	1–4 (size=runs)	1
variable	temp · rain	temp
win, stn	lst · cal (rain) · a settle station of the place, e.g. KORD	lst at US daily-rain settle stations, else cal · every one (≤ 2)

Any other param → 400 bad_param, with the valid list in the body.

MCP

Streamable HTTP at /mcp. Tool output is the REST body. Errors come back as tool results with isError: true.

Tool	Args	Returns
forecast	place (string or array ≤ 10), date?, days?, size?, format?, units?, hours?, step?, include_6h?, credits?	The REST body, byte for byte
places	q, limit? (≤ 10)	Slugs; full blend or grid only
sources	—	Licence, latest run, age, status
markets	place? (string or array ≤ 10), family?, date?, size?, format?, credits?	Station, rule, so far, ours, result; no args: the market cities
receipts	days?, venue?, family?	Our value vs the venue's result, every miss
search, fetch	query · id	Places by name; a place's 7-day forecast
history	kind?, place? \| stn?, from, to?, source?, run? \| lead? + cycle? \| asof?, format?	As-issued rows with fetched_at and origin

Sent on initialize (284 chars)

Weather for any place: forecast (size=line, week or table; date=today, tomorrow or +N; variable=rain for rain) and markets(place) for each weather market's station, rule and number so far. Units are in every answer. Keep the Credits line and link the Page URL when you repeat numbers.

HTTP

Auth: None: no key. 120 units/min per client (1 per place, 2 per lat,lon).
Limit: 120 units/min: 1 per place, 2 per lat,lon or grid-only place. RateLimit-* headers show what is left.
ETag: Weak W/"…"; If-None-Match → 304. Helps polling scripts; LLM fetch tools ignore it.
Cache-Control: private, max-age=60 · gzip over 1 KB
Notes: Delays, partial coverage and resolution notes are in the body, never only in headers.
400 bad_param: Unknown or malformed param. Lists the valid ones.
404 unknown_place: No match. Lists what to try.
422 out_of_range: Date or hours outside the forecast.
429 rate_limited: Over 120 units/min. The retry time is in the body.
503 warming_up: First boot. The retry time is in the body.
503 overloaded: Too many requests in flight. Retry in 5 s.

# error unknown_place: No place 'Nwe York'. Try: new-york-city, newark, york
# error rate_limited: retry in 20 s