SVG Synastry Chart Generator

POST/api/v1/natal/chart/synastry

Generate a true synastry bi-wheel SVG/PNG chart using person A as the reference frame, with person B overlaid. Supports independent planet colors, aspect visibility toggles, secondary house ring/angles, and independent A/B lane background colors.

Related SVG Endpoints

Synastry is the bi-wheel relationship view. If you want one standalone chart from two people, use the midpoint composite endpoint instead.

SVG Composite Chart

Single composite wheel built from midpoint positions.

SVG Natal Chart

Single-person natal SVG/PNG rendering.

Full URL

https://api.freeastroapi.com/api/v1/natal/chart/synastry

Top-level Parameters

Request-level controls specific to the synastry endpoint.

Parameter	Type	Required	Default	Description
person_a	object	Yes	-	Primary person object using the same birth-data fields as the SVG/PNG Chart Generator.
person_b	object	Yes	-	Secondary person object using the same birth-data fields as the SVG/PNG Chart Generator.
show_a_aspects	boolean	No	false	Show aspect lines inside person A set.
show_inter_aspects	boolean	No	true	Show aspect lines between person A and person B.
show_b_aspects	boolean	No	false	Show aspect lines inside person B set.
person_a_planet_color	string\|null	No	#1565C0	Color override for person A planets and degree labels.
person_b_planet_color	string\|null	No	#C62828	Color override for person B planets and degree labels.
person_a_angle_color	string\|null	No	#1A1A1A	Color override for person A angle glyphs (ASC/MC/DSC/IC).
person_b_angle_color	string\|null	No	#1A1A1A	Color override for person B angle glyphs (ASC/MC/DSC/IC).
show_person_b_houses	boolean	No	true	Render secondary house ring (only when person_b.time_known=true).
show_person_b_angles	boolean	No	true	Render secondary angle axes and angle glyphs (only when person_b.time_known=true).
person_a_zone_bg_color	string\|null	No	null	Background color for person A planet lane.
person_a_zone_bg_opacity	float\|null	No	null	Opacity for person A lane background (0.0 to 1.0).
person_b_zone_bg_color	string\|null	No	null	Background color for person B planet lane.
person_b_zone_bg_opacity	float\|null	No	null	Opacity for person B lane background (0.0 to 1.0).

person_a / person_b Schema

Both nested objects use the same birth-data schema as the SVG/PNG Chart Generator.

Parameter	Type	Required	Default	Description
name	string	No	User	Display name for the person.
year	integer	Yes	-	Birth year.
month	integer	Yes	-	Birth month (1-12).
day	integer	Yes	-	Birth day (1-31).
hour	integer	No	12	Birth hour (0-23).
minute	integer	No	0	Birth minute (0-59).
time_known	boolean	No	true	Set false if time is unknown. Houses/angles are removed for that person.
city	string	No	-	Birth city. Optional when lat/lng are provided.
lat	float	No	auto	Optional latitude override. Required with lng if city is omitted.
lng	float	No	auto	Optional longitude override. Required with lat if city is omitted.
tz_str	string	No	AUTO	Timezone or AUTO.
format	string	No	svg	Output format: 'svg' or 'png' (from person_a).
size	integer	No	700	Output width/height in px (from person_a).
theme_type	string	No	light	Theme: 'light', 'dark', 'mono' (from person_a).
display_settings	object	No	null	Per-person body visibility toggles (sun, moon, mercury... asc/mc, nodes, asteroids).
chart_config	object	No	null	Advanced chart styling controls shared with the SVG/PNG Chart Generator.

display_settings (nested)

Optional body visibility toggles inside each person object.

Parameter	Type	Required	Default	Description
sun..pluto	boolean	No	true	Show or hide major planets.
north_node	boolean	No	true	Show North Node.
asc	boolean	No	true	Show Ascendant glyph.
mc	boolean	No	false	Show Midheaven glyph.
chiron / asteroids / lilith	boolean	No	false	Optional extras.

chart_config (nested)

Optional advanced styling settings shared with the SVG/PNG Chart Generator.

Parameter	Type	Required	Default	Description
custom_sign_bg_color	string	No	null	Single sign background color.
custom_house_bg_color	string	No	null	Single house background color.
show_retrograde_markers	boolean	No	false	Show retrograde marker on degree text.
retrograde_marker_style	string	No	R	R or rx.
houses_inside_planets	boolean	No	true	Preferred layout for synastry bi-wheel.
line/ring/aspect widths + colors	various	No	varies	Advanced visual style controls.

Sample Code

curl -X POST "https://api.freeastroapi.com/api/v1/natal/chart/synastry" \
 -H "Content-Type: application/json" \
 -H "x-api-key: YOUR_API_KEY" \
 -d '{
  "person_a": {
    "name": "Person A",
    "year": 1990,
    "month": 5,
    "day": 15,
    "hour": 14,
    "minute": 30,
    "time_known": true,
    "city": "London",
    "tz_str": "AUTO",
    "format": "svg",
    "size": 900,
    "theme_type": "light"
  },
  "person_b": {
    "name": "Person B",
    "year": 1992,
    "month": 8,
    "day": 6,
    "hour": 6,
    "minute": 45,
    "time_known": true,
    "city": "Paris",
    "tz_str": "AUTO"
  },
  "show_a_aspects": false,
  "show_inter_aspects": true,
  "show_b_aspects": false,
  "person_a_planet_color": "#1565C0",
  "person_b_planet_color": "#C62828",
  "person_a_angle_color": "#1A1A1A",
  "person_b_angle_color": "#1A1A1A",
  "show_person_b_houses": true,
  "show_person_b_angles": true,
  "person_a_zone_bg_color": "#fde3e3",
  "person_a_zone_bg_opacity": 0.55,
  "person_b_zone_bg_color": "#e3ecff",
  "person_b_zone_bg_opacity": 0.55
}' --output synastry_chart.svg

Sample Output (PNG)