OhMyWind

Wind, sea, and where it matters current and tide, at one point. For the questions about a place rather than a passage: how hard it blows at Groix this afternoon, when the thermal breeze fills in, when the mistral eases, whether the models agree, what the swell does at a harbour entrance tonight. Args: lat: latitude in degrees. lon: longitude in degrees. start: ISO-8601 datetime with the user's UTC offset (e.g. "2026-05-01T08:00:00+02:00"). Every time in the answer comes back in that offset. end: ISO-8601 datetime, timezone-aware. models: optional list of model names. Leave it unset for the automatic choice: AROME (1.3 km) wherever it reaches the window, and the next model that reaches its end when the window runs past two days. Name several models (``["arome", "icon_eu", "ecmwf", "gfs"]``) only when the user asks whether the models agree: each one costs a request. Returns hourly ``wind`` per model (speed, direction it comes from, gusts, in knots), ``sea`` (wave height, period, direction), and, only where they are material, ``current`` (speed in knots, direction it flows to, from a tidal atlas where one covers the point) and ``tide`` (height around mean sea level: read the range and the times of high and low water from it, not a depth over chart datum). Each series is a table: ``columns`` names the fields once, each of ``rows`` is one hour. Also ``openwind_url``, the OhMyWind map centred on the point. Answer in a sentence first (the user is often in a car or at the bar), then give the few numbers that back it, as a short table or a small chart if your interface draws one. No widget comes with this tool: the presentation is yours. Offer ``openwind_url`` as "voir sur la carte". This is a forecast: never present it as a measurement of what is blowing right now. Pass a point at sea. Open-Meteo Marine answers from the nearest sea cell: a few kilometres inland the ``sea`` values are the open coast's (Guipavas, inland of Brest, gets the waves of the rade), further inland they come back null, the ``sea`` array present and empty of information rather than absent. Wind is always the point's own. Note: the first request after inactivity may incur ~5s of cold-start.

The tidal stream and the tide at one point, from the tidal atlases alone. For the questions about a pass or a harbour entrance: when to be at the Raz de Sein to carry the stream, when the Fromveur turns, how hard it runs at Port-Navalo tomorrow, when high water is at Chausey. Costs no weather request: harmonic predictions from the atlases this server ships (SHOM, MARC and others), the same ones ``plan_passage`` applies leg by leg. Args: lat: latitude in degrees, at sea, in the pass itself. lon: longitude in degrees. start: ISO-8601 datetime with the user's UTC offset; every time in the answer comes back in that offset. end: ISO-8601 datetime, timezone-aware. At most 400 steps. heading_deg: optional course through the point (true degrees, the direction you head to). With it, each step gets ``along_kn`` (positive: the stream carries you, negative: it stems you) and the answer lists the ``favourable`` and ``adverse`` windows. step_minutes: 5 to 180, default 30. Returns ``covered``, ``source``, ``confidence``, ``points`` (a table: ``columns`` time, ``speed_kn``, ``direction_to_deg`` it flows to, ``along_kn``, ``height_m`` around mean sea level; one row per step), ``slack`` (the moments the stream nearly stops), ``high_waters`` / ``low_waters``, ``favourable`` / ``adverse`` when a heading is given, ``tide_coefficient`` (French national coefficient, Brest, on French atlases), a ``warning`` when the atlas does not resolve the pass, and ``openwind_url``. Outside every atlas (most of the Mediterranean, the open sea) ``covered`` is false: say so, and use ``get_marine_forecast``, which returns the global model's current where it matters. Astronomical tide only: no surge, no wind-driven current. The windows are facts about the stream, not a recommendation: weigh them against the wind (``get_marine_forecast``) and the whole passage (``plan_passage``). Present the answer yourself, the time to be at the pass in one sentence and the few times that back it: no widget comes with this tool.

List the boat archetypes with descriptive metadata. The LLM (or user) maps a commercial model (e.g. "Sun Odyssey 32") to one of these archetypes from the metadata — there is no server-side mapping. ``voile_aviron_16ft`` is for open sail-and-oar dinghies only (no cabin, rowed as well as sailed); a small cabin cruiser maps to ``cruiser_20ft``.

Plan an A→B passage. Compare departure windows by default; pin a single departure only when the user gives an explicit time. ## Tool routing: read this first Before calling, classify the user's question: 1. **Pure weather lookup at a point** ("y aura-t-il du vent à Cassis samedi à 14h ?", "quelles vagues dimanche au cap Sicié ?"): call ``get_marine_forecast`` and answer in text. Do NOT call ``plan_passage``: there's no route to plan. 2. **Trajet question with a flexible date** ("Marseille → Porquerolles ce week-end", "demain ou après-demain", "dans les prochains jours"): call ``plan_passage`` in **compare-windows mode**, passing ``latest_departure`` (e.g. earliest+48h) and ``sweep_interval_hours`` (3 or 6 typically) so the user sees several departure scenarios side-by-side. Then pick 2-3 good ones and let the user choose. This is the **default** for trajet planning: same API cost as a single passage thanks to cache prewarm, much more value. 3. **Trajet with a precise hour pinned by the user** ("je pars demain à 8h", "départ Saturday 9am"): call ``plan_passage`` in single mode (no ``latest_departure``). Used for the final "show me the detailed plan for THIS departure" view, often after step 2. 4. **Two ways to go** ("nord ou sud du Fromveur pour Ouessant ?", "par l'intérieur ou l'extérieur des Glénan ?", "Ré ou Aix demain ?"): one ``plan_passage`` call, the first route in ``waypoints`` and the others in ``alternatives`` (two at most), each with a short ``label`` saying how it goes ("Par le nord du Fromveur"). Every route is computed for the same departures, so the widget compares them cell by cell. Do not make one call per route. 5. **When to be at a pass** ("à quelle heure au Raz de Sein ?", "quand renverse le courant au Fromveur ?"): ``get_tidal_stream`` at the pass, with the course you will steer, and ``plan_passage`` comparing departures, both in the same turn; then pick the departure that brings you there in the favourable window. 6. **Methodology question** ("comment c'est calculé ?", "quelle efficacité par défaut ?"): call ``read_me``. Rule of thumb: if the user does NOT give an exact hour, prefer compare-windows. The widget renders one of the windows by default and the chat lets the user pick another. ## Waypoints must stay in the water This server runs a coarse land check before anything else: a leg that runs a couple of kilometres over land, or a waypoint inland, gets the call refused before any forecast request, with the leg and the place named. Redraw it and call again; never show the user a route over land. The shoreline is coarse (about 1 km, the coast widened by 2 km so harbours stay at sea, and any water a fine current atlas resolves counts as sea): a spit narrower than about 4 km, or a leg that shaves a headland, passes the check and is timed as drawn, too short, too fast, and scored on conditions the boat would never meet. So the route is still yours to draw. Between every consecutive pair of waypoints the straight line must stay at sea. Add intermediate waypoints to round anything the direct line would cut: headlands, peninsulas, islands, shoals. - Toulon to Saint-Tropez: the direct line crosses the Massif des Maures. Pass south of the presqu'île de Giens, then round cap Bénat and cap Camarat before turning north into the gulf. - Brest to Douarnenez: the direct line crosses the presqu'île de Crozon. Exit the goulet, round the cap de la Chèvre, then head east into the bay. Keep about 1 NM of clearance off headlands, more with onshore wind or swell, and do not shave the inside of islands. Extra waypoints are close to free: the cap is 50, and sampling cost follows ``segment_length_nm`` and total distance, not the waypoint count. When in doubt, add the waypoint. A waypoint that lands ashore has a second effect. Open-Meteo returns no sea state over land, so those samples carry a null wave height and the complexity score silently falls back to wind only, dropping the axis that would have flagged a rough passage. Name the capes you routed around in your reply ("passage au large du cap Bénat"), so the user can correct a leg you drew wrong. ## Returned payload Every time comes back in the UTC offset of ``departure``: send the user's own (``+02:00`` for France in summer) and read the times as their clock. Single mode: - ``passage``: per-segment timing report (distance_nm, duration_h, model used, segments[] with TWS/TWA/boat_speed/Hs, warnings). - ``complexity``: 1-5 difficulty score with wind/sea breakdown and a human-readable rationale. - ``openwind_url``: deep-link to ohmywind.fr/plan that renders the same passage in the standalone web app. - ``waypoints``: the route as you sent it, which the widget draws on a map. - ``route_label`` and ``alternatives[]``, only when you passed alternatives: each alternative has its ``label``, ``waypoints``, ``passage``, ``complexity`` and ``openwind_url``. - ``disclaimer``: usage warning to relay (see below). Compare-windows mode (``latest_departure`` set): - ``mode``: ``"multi_window"``. - ``sweep``: ``earliest`` / ``latest`` / ``interval_hours`` / ``window_count``. - ``windows[]``: each entry has ``departure``, its ``weekday``, ``arrival``, ``duration_h``, ``distance_nm``, ``complexity`` (level + label + rationale), ``conditions_summary`` (tws_min/max, predominant sail angle, hs_min/max), ``warnings`` (the difficulty first), ``openwind_url``. - ``meta_warnings``: notes about the whole sweep or the route ("3 fenêtres ignorées …", a long route sampled more sparsely). - ``waypoints``: the route as you sent it, once for all windows. - ``route_label`` and ``alternatives[]``, only when you passed alternatives: each alternative has its ``label``, ``waypoints`` and its own ``windows[]``, same departures. - ``disclaimer``: usage warning to relay (see below). ## ALWAYS relay the disclaimer This tool returns an ETA and a difficulty score the user may act on to decide whether to put to sea. Carry the ``disclaimer`` field into your reply, once, in the user's language, phrased naturally rather than quoted verbatim. Put it after the numbers, not before: it qualifies them, it does not replace them. Do not drop it because the plan looks easy, and do not repeat it on every follow-up turn about the same passage. ## How it renders On hosts that support MCP Apps (Claude, Claude Desktop, ChatGPT, VS Code Copilot, Goose, Postman, MCPJam), the response is automatically accompanied by an interactive widget served via the ``ui://openwind/plan-passage`` resource declared on this tool's ``_meta``. In compare-windows mode it lists the departures; the one the user selects (the earliest at first) drives a map of the route you drew, coloured by its wind, and its per-leg detail. In single mode it shows the figures, the map and the per-leg detail. The user sees your waypoints on that map, one more reason to keep every leg at sea. On hosts without MCP Apps support (Cursor, Le Chat, terminal), present a short text summary of the result (route, ETA, complexity, warnings) and offer ``openwind_url`` as the link to adjust the route or the departure on the site. ## Offer the openwind_url(s) in your text reply Even when the widget renders inline, the link is useful spelled out: it opens this very plan in the web app, where the user can drag the route, move the departure or change the boat, and share or bookmark it. - **Single mode**: end your reply with a Markdown link built from the ``openwind_url`` field, e.g. ``[Modifier le tracé ou le départ →](<openwind_url>)``. Always use that value verbatim, never a URL you compose yourself: it points at the environment this server is configured for, which is not always the production site. - **Compare-windows mode**: list 2-4 of the most relevant windows and give each its own link, e.g. ``- Sam 2 mai 09h · 11h12 · ⚡2/5 · [voir →](url)``. The widget lets the user inspect any window, but it does not rank them: your picks and their links still belong in the reply. Phrase the link with intent, as what the user can do there ("modifier le tracé ou le départ", "ajuster ce départ dans l'app"), not just a bare URL: the user should know what clicking does. ## Args waypoints: list of ``{"lat": ..., "lon": ...}`` dicts, 2 to 50. Used exactly as drawn. Read "Waypoints must stay in the water" above before building it. departure: ISO-8601 datetime, timezone-aware. archetype: the boat. Pick it yourself from what the user sails, among these (``list_boat_archetypes`` returns the same list): - ``cruiser_20ft``: 20 ft (6 m) monohull, slow (Beneteau First 210, Catalina 22, Jeanneau Tonic 23) - ``cruiser_25ft``: 25 ft (8 m) monohull, slow (Beneteau First 25, Catalina 25, Jeanneau Sun Odyssey 24) - ``cruiser_30ft``: 30 ft (9 m) monohull, slow (Sun Odyssey 32, Bavaria 31, Beneteau Oceanis 31) - ``cruiser_40ft``: 40 ft (12 m) monohull, average (Sun Odyssey 410, Bavaria 41 Cruiser, Hanse 418) - ``cruiser_50ft``: 50 ft (15 m) monohull, fast (Sun Odyssey 519, Bavaria C50, Hanse 508) - ``catamaran_40ft``: 40 ft (12 m) catamaran, fast-reach (Lagoon 40, Bali 4.1, Fountaine Pajot Lucia 40) - ``racer_cruiser``: 40 ft (12 m) monohull, very-fast (J/122, Pogo 12.50, Solaris 40) - ``voile_aviron_16ft``: 16 ft (5 m) monohull, slow (Vivier Ilur, Vivier Aven, Vivier Aber) ``voile_aviron_16ft`` is an open sail-and-oar dinghy only; a small cabin cruiser is ``cruiser_20ft``. efficiency: multiplier on polar speed. ``0.85`` racing, ``0.75`` cruising (default), ``0.65`` loaded family cruising, ``0.55`` heavy seas / fouled hull. segment_length_nm: target sub-segment length. Default 10 nm balances precision vs Open-Meteo budget; drop to 5 for tight coastal work, raise to 20 for long offshore legs. model: wind model. Default ``"auto"`` tries AROME (≤48 h) → ICON-EU (≤5 d) → ECMWF IFS 0.25° (≤10 d) → GFS (≤16 d). Pass ``arome``, ``icon_eu``, ``ecmwf`` or ``gfs`` to bypass. max_hs_m: optional max significant wave height (meters) over the route: pass it if you have a sea-state estimate from ``get_marine_forecast`` and want it factored into the score. Defaults to wind-only scoring. motor_threshold_kn: optional sail-speed floor (knots) under which the simulator switches to engine power. Must be paired with ``motor_speed_kn`` (either alone is ignored). Typical value 2 kn: sailors fire up the engine rather than crawl in light wind. Leave unset for 100% sail. Range (0, 10]. motor_speed_kn: optional speed under engine (knots) applied to segments where the sail estimate falls under ``motor_threshold_kn``. Typical 5-6 kn for a cruising boat. Range (0, 12]. min_upwind_twa_deg: optional minimum sailable TWA (degrees) overriding the archetype's own value (42-50 deg depending on the boat). Pass it when you know the boat points better or worse than the archetype suggests. Range [25, 70]. route_label: optional short name for the main route, shown in the widget when you pass alternatives ("Par le nord"). alternatives: optional other routes for the same trip, at most two: ``[{"label": "Par le sud", "waypoints": [...]}, ...]``. Same departures, same boat, same rules for the waypoints (stay at sea). Each route costs its own forecast requests: pass them only when the user weighs two ways to go. inland_waterway: true only when the user sails up a river or a canal the coarse shoreline counts as land (the Seine to Rouen, the Loire to Nantes): it turns the land check off for this call. Never set it to get past a refusal at sea; redraw the route instead. ## Compare-windows mode (latest_departure set) When ``latest_departure`` is provided, the tool switches into a window-comparison call: it walks departure times from ``departure`` up to ``latest_departure`` every ``sweep_interval_hours`` (default 1 h). Returns ``{"mode": "multi_window", "sweep": {...}, "windows": [...]}`` instead of the single-passage payload. Each window contains ``departure``, ``arrival``, ``duration_h``, ``distance_nm``, ``complexity``, ``conditions_summary``, ``warnings``, and its own ``openwind_url``. ``target_eta``: optional ISO-8601 datetime. When set, only windows that arrive within ±2 h of the target are returned. If none match, all windows are returned with a ``meta_warnings`` note. ## Failure modes Raises ``ForecastHorizonError`` if the chosen model's horizon doesn't cover the passage and ``model != "auto"``. The error message names the failing model and suggests longer-range alternatives.

Return OhMyWind's calculation methodology as Markdown. Call this when the user asks how passage timing, complexity, or boat speed are computed (e.g. "comment c'est calculé ?", "what assumptions does the model use?", "is tacking modelled?"). The returned text covers: polar lookup, default efficiency 0.75, VMG / tacking correction, wave derate, single-pass timing, compare-windows mode semantics, regional defaults, wind against current, short-period chop, what is intentionally not modelled, and the data attributions.