{"uid":"cap_sLX5e_2PoB7MpS3zpsusN","slug":"almanac-earth-magnetic-field-api-2e15e9cd","name":"Almanac Earth Magnetic Field API","description":"Deterministic WMM2025 magnetic field (one location/date). Free sample, no payment required: GET /play/field","url":"https://almanac.locomot.io/field","method":"GET","headers":{},"bodySchema":{"type":"object","$schema":"https://json-schema.org/draft/2020-12/schema","required":["input"],"properties":{"input":{"type":"object","required":["type","method"],"properties":{"type":{"type":"string","const":"http"},"method":{"enum":["GET","HEAD","DELETE"],"type":"string"},"queryParams":{"type":"object","required":["lat","lon"],"properties":{"lat":{"type":"number","maximum":90,"minimum":-90},"lon":{"type":"number","maximum":180,"minimum":-180},"when":{"type":"string","description":"ISO date / decimal year; default now"},"altitude_km":{"type":"number","description":"optional, default 0; WMM valid [-1,850]"}}}},"additionalProperties":false},"output":{"type":"object","properties":{"model":{"type":"string"},"query":{"type":"object"},"units":{"type":"object"},"engine":{"type":"string"},"down_Z_nT":{"type":"number"},"east_Y_nT":{"type":"number"},"north_X_nT":{"type":"number"},"model_epoch":{"type":"number"},"valid_range":{"type":"array"},"compass_note":{"type":"string"},"deterministic":{"type":"boolean"},"declination_deg":{"type":"number"},"inclination_deg":{"type":"number"},"secular_variation":{"type":"object"},"total_intensity_nT":{"type":"number"},"horizontal_intensity_nT":{"type":"number"}}}}},"responseSchema":null,"example":null,"exampleRequest":null,"tags":["x402"],"displayCostAmount":"0.002","displayCostAsset":"USDC","priceDynamic":false,"priceHint":null,"priceStatus":"priced","priceSource":"probe","requiresHandshake":false,"reviewCount":0,"rating":{"score":"0.00","successRate":"0.00","reviews":0,"stars":null,"state":"unrated"},"availabilityStatus":"unknown","priceObserved":null,"sessionDeposit":null,"pricing":{"kind":"static","summary":"$0.002/call","primary":{"kind":"static","protocol":"x402","network":"base","amountUsd":"0.002","per":"call","confidence":"exact"},"accepted":[{"kind":"static","protocol":"x402","network":"base","amountUsd":"0.002","per":"call","confidence":"exact"}]},"paymentMethods":[{"uid":"pm_MGDXKIdol_6xcrLoX7sdJ","protocol":"x402","methodType":"crypto","chain":"base","mode":"charge","costAmount":"0.002","costPer":"request","priority":0,"asset":"0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913","unit":"request","depositMicros":null,"planRef":null}],"brandName":null,"brandSlug":null,"brandBaseUrl":null,"brandDocsUrl":null,"whatItDoes":"Returns Earth's geomagnetic field components (declination, inclination, intensity) for a given latitude/longitude using the World Magnetic Model (WMM)","exampleAgentPrompt":"What's the magnetic declination and total field intensity at latitude 37.7749, longitude -122.4194 right now, at ground level?","exampleUseCases":null,"resultDescription":"Returns a JSON object with geomagnetic field components including declination (degrees), inclination/dip angle (degrees), total field intensity (nanoTeslas), horizontal intensity, north/east/down vector components, secular variation rates, the WMM model epoch and valid range, and a human-readable compass note explaining the magnetic offset from true north.","failureModes":["Missing required lat or lon parameters returns a 400 error","Latitude out of range [-90,90] or longitude out of range [-180,180] returns validation error","Invalid ISO date string for 'when' parameter causes parse error","Altitude outside WMM valid range [-1, 850 km] may return warning or error","Unpaid or insufficient x402 payment returns 402 Payment Required","Date outside WMM model valid range returns an out-of-range error"],"whenToPreferThis":"Use this endpoint when you need precise geomagnetic field data (declination, inclination, intensity) derived from the authoritative World Magnetic Model — ideal for compass calibration, navigation correction, drone/aviation systems, surveying, or any application requiring the difference between true north and magnetic north at a specific point on Earth. Prefer this over lookup tables or approximations when accuracy and current secular variation matter.","instructions":null,"reviewSummary":null,"reviewSummaryHighlights":null,"reviewSummaryConcerns":null,"reviewSummaryGeneratedAt":null,"activationCount":0,"lastUsedAt":null,"lastSuccessfullyRanAt":null,"lastHealthCheckAt":"2026-09-15T12:43:11.555Z","isFirstParty":false}