diff --git a/.github/copilot-instructions.md b/.github/copilot-instructions.md
index 4336990a..6ef0b2f2 100644
--- a/.github/copilot-instructions.md
+++ b/.github/copilot-instructions.md
@@ -56,7 +56,7 @@ applyTo: '/**'
 * Do not repeat concept definitions inline in tutorials or docstrings, link to the glossary instead using a relative markdown link (e.g. `[moneyness](../glossary.md#moneyness)`).
 * Use relative links for all mkdocs page links (e.g. `[Option Pricing](../theory/option_pricing.md)`) — prefer relative over absolute URLs to keep links shorter and portable.
 * Prefer mkdocstrings relative cross-references whenever the target is visible from the current scope: write `[label][.member]` (same class) or `[label][..Sibling]` (same module) instead of repeating the fully-qualified path. Use the full path only when the target lives in a different module than the current docstring.
-* To rebuild doc examples run `uv run ./dev/build-examples` — runs all scripts in `docs/examples/` and writes their output to `docs/examples/output/`
+* To rebuild doc examples run `uv run python dev/tools/build_examples.py` — runs all scripts in `docs/examples/` and writes their output to `docs/examples/output/`
 
 ## Pydantic models
 
diff --git a/.github/workflows/examples.yml b/.github/workflows/examples.yml
index af31d5c2..20e1a6c4 100644
--- a/.github/workflows/examples.yml
+++ b/.github/workflows/examples.yml
@@ -25,7 +25,7 @@ jobs:
       - name: Install dependencies
         run: uv sync --frozen --no-install-project --group docs --extra data
       - name: build examples
-        run: uv run ./dev/build-examples
+        run: uv run python dev/tools/build_examples.py
       - name: upload examples output
         if: inputs.upload
         uses: actions/upload-artifact@v4
diff --git a/.vscode/launch.json b/.vscode/launch.json
index 37d7d864..fefb53cc 100644
--- a/.vscode/launch.json
+++ b/.vscode/launch.json
@@ -2,6 +2,18 @@
     "version": "0.2.0",
     "configurations": [
 
+        {
+            "name": "Record Fixtures",
+            "type": "debugpy",
+            "request": "launch",
+            "cwd": "${workspaceFolder}",
+            "console": "integratedTerminal",
+            "program": "dev/tools/record_fixtures.py",
+            "justMyCode": false,
+            "args": [
+                "--dry-run",
+            ]
+        },
         {
             "name": "PyTest",
             "type": "debugpy",
diff --git a/Makefile b/Makefile
index b75360c0..3cd8bbec 100644
--- a/Makefile
+++ b/Makefile
@@ -12,21 +12,25 @@ app-serve:			## serve python api app only
 .PHONY: docs
 docs:				## build documentation
 	@cp docs/index.md readme.md
-	@uv run ./dev/build-examples
+	@uv run python dev/tools/build_examples.py
 	@uv run mkdocs build --strict
 
 .PHONY: docs-bib
 docs-bib:			## Regenerate docs bibliography
-	@uv run ./docs/bib2md.py
+	@uv run python dev/tools/bib2md.py
 
 .PHONY: docs-examples
 docs-examples:			## Regenerate docs examples
-	@uv run ./dev/build-examples
+	@uv run python dev/tools/build_examples.py
 
 .PHONY: docs-serve
 docs-serve:			## serve docs, examples, and API with auto-reload
 	@bash ./dev/serve/all
 
+.PHONY: fixtures
+fixtures:			## Record market data fixtures from live sources
+	@uv run python dev/tools/record_fixtures.py
+
 .PHONY: frontend-build
 frontend-build:			## build Observable frontend examples
 	@rm -rf app/examples
diff --git a/dev/quantflow.dockerfile b/dev/quantflow.dockerfile
index 623f2c45..c02397d8 100644
--- a/dev/quantflow.dockerfile
+++ b/dev/quantflow.dockerfile
@@ -18,7 +18,7 @@ RUN uv sync --frozen --no-install-project --group docs --extra data
 
 # Copy source and build docs
 # Example outputs and images must be prebuilt in the build context
-# (run `uv run ./dev/build-examples` locally, or the build-examples CI job)
+# (run `uv run python dev/tools/build_examples.py` locally, or the build-examples CI job)
 COPY mkdocs.yml ./
 COPY dev/ ./dev/
 COPY docs/ ./docs/
diff --git a/docs/bib2md.py b/dev/tools/bib2md.py
similarity index 98%
rename from docs/bib2md.py
rename to dev/tools/bib2md.py
index 3764f31a..9e996607 100644
--- a/docs/bib2md.py
+++ b/dev/tools/bib2md.py
@@ -2,7 +2,7 @@
 """Convert docs/references.bib to docs/bibliography.md.
 
 Usage:
-    uv run python docs/bib2md.py [--bib PATH] [--out PATH]
+    uv run python dev/tools/bib2md.py [--bib PATH] [--out PATH]
 
 The BibTeX file is the source of truth; run this script whenever it changes.
 """
@@ -179,7 +179,7 @@ def convert(bib_path: Path, out_path: Path) -> None:
 
 
 def main() -> None:
-    docs = Path(__file__).parent
+    docs = Path(__file__).parent.parent.parent / "docs"
     parser = argparse.ArgumentParser(description=__doc__)
     parser.add_argument(
         "--bib",
diff --git a/dev/build-examples b/dev/tools/build_examples.py
similarity index 100%
rename from dev/build-examples
rename to dev/tools/build_examples.py
diff --git a/dev/tools/record_fixtures.py b/dev/tools/record_fixtures.py
new file mode 100644
index 00000000..c3b5107c
--- /dev/null
+++ b/dev/tools/record_fixtures.py
@@ -0,0 +1,88 @@
+"""Record market data fixtures from live sources.
+
+Each recorder fetches live data, trims it down to the fields consumed by the
+loaders and writes it to docs/examples/fixtures. The regularMarketTime entry
+of the underlying quote is preserved so loaders can recover the as of date of
+the snapshot.
+"""
+
+import asyncio
+import gzip
+import json
+from datetime import datetime, timezone
+from typing import Awaitable, Callable
+
+import click
+
+from docs.examples._utils import FIXTURES
+from quantflow.data.yahoo import Yahoo
+
+OPTION_FIELDS = ("strike", "bid", "ask", "openInterest", "volume")
+QUOTE_FIELDS = ("bid", "ask", "regularMarketPrice", "regularMarketTime")
+
+
+def trim_chain(chain: dict) -> dict:
+    """Trim a Yahoo option chain payload to the fields used by the loaders"""
+    quote = chain.get("quote") or {}
+    return {
+        "underlyingSymbol": chain.get("underlyingSymbol", ""),
+        "quote": {key: quote.get(key) for key in QUOTE_FIELDS},
+        "options": [
+            {
+                "expirationDate": expiry["expirationDate"],
+                "calls": trim_contracts(expiry.get("calls", [])),
+                "puts": trim_contracts(expiry.get("puts", [])),
+            }
+            for expiry in chain.get("options", [])
+        ],
+    }
+
+
+def trim_contracts(contracts: list[dict]) -> list[dict]:
+    return [
+        {key: c.get(key) for key in OPTION_FIELDS if c.get(key) is not None}
+        for c in contracts
+    ]
+
+
+async def record_yahoo(dry_run: bool) -> None:
+    """Record the SPX option chain fixture from Yahoo Finance"""
+    async with Yahoo() as cli:
+        chain = await cli.option_chain("^SPX")
+    trimmed = trim_chain(chain)
+    path = FIXTURES / "yahoo_spx.json.gz"
+    expiries = len(trimmed["options"])
+    as_of = "unknown"
+    if market_time := trimmed["quote"].get("regularMarketTime"):
+        as_of = datetime.fromtimestamp(market_time, tz=timezone.utc).isoformat()
+    if dry_run:
+        click.echo(
+            f"dry run, would record {path} as of {as_of} with {expiries} expiries"
+        )
+        return
+    path.write_bytes(gzip.compress(json.dumps(trimmed).encode()))
+    click.echo(f"recorded {path} as of {as_of}")
+
+
+RECORDERS: dict[str, Callable[[bool], Awaitable[None]]] = {
+    "yahoo": record_yahoo,
+}
+
+
+@click.command()
+@click.argument("sources", nargs=-1, type=click.Choice(sorted(RECORDERS)))
+@click.option(
+    "--dry-run", is_flag=True, help="Fetch and trim but do not write fixture files."
+)
+def main(sources: tuple[str, ...], dry_run: bool) -> None:
+    """Record market data fixtures from live sources.
+
+    With no arguments all fixtures are recorded, otherwise only the given
+    SOURCES are recorded.
+    """
+    for name in sources or sorted(RECORDERS):
+        asyncio.run(RECORDERS[name](dry_run))
+
+
+if __name__ == "__main__":
+    main()
diff --git a/docs/examples/fixtures/yahoo_spx.json.gz b/docs/examples/fixtures/yahoo_spx.json.gz
index 2789fe68..b5b504fa 100644
Binary files a/docs/examples/fixtures/yahoo_spx.json.gz and b/docs/examples/fixtures/yahoo_spx.json.gz differ
diff --git a/docs/glossary.md b/docs/glossary.md
index 6155f76f..557737d9 100644
--- a/docs/glossary.md
+++ b/docs/glossary.md
@@ -108,7 +108,7 @@ the forward-space prices are
 
 Forward-space prices are dimensionless and depend only on the
 [log-strike](#log-strike) $k = \log(K/F)$, the implied volatility,
-and the time to maturity. They are the natural output of Fourier-based
+and the [time to maturity](#time-to-maturity-ttm). They are the natural output of Fourier-based
 pricers and of [Black pricing](api/options/black.md).
 
 The conversion to quote-currency prices is a single multiplication by $F$:
@@ -166,7 +166,7 @@ Moneyness is used in the context of option pricing in order to compare options w
     m = \frac{1}{\sqrt{\tau}}\ln{\frac{K}{F}} = \frac{k}{\sqrt{\tau}}
 \end{equation}
 
-where $K$ is the strike, $F$ is the Forward price, and $\tau$ is the time to maturity. It is used to compare options with different maturities by scaling the [log-strike](#log-strike) by the square root of time to maturity. This is because the price of the underlying asset is subject to random fluctuations, if these fluctuations follow a Brownian motion than the standard deviation of the price movement will increase with the square root of time.
+where $K$ is the strike, $F$ is the Forward price, and $\tau$ is the [time to maturity](#time-to-maturity-ttm). It is used to compare options with different maturities by scaling the [log-strike](#log-strike) by the square root of time to maturity. This is because the price of the underlying asset is subject to random fluctuations, if these fluctuations follow a Brownian motion then the standard deviation of the price movement will increase with the square root of time.
 
 
 ## Moneyness Convexity Adjusted
@@ -177,7 +177,7 @@ The convexity-adjusted moneyness, often called standardized moneyness in the lit
     m_c = \frac{1}{\sigma\sqrt{\tau}}\ln\frac{K}{F} + \frac{\sigma\sqrt{\tau}}{2} = m_\sigma + \frac{\sigma\sqrt{\tau}}{2} = -d_2
 \end{equation}
 
-where $K$ is the strike, $F$ is the Forward price, $\tau$ is the time to maturity, $\sigma$ is the implied Black volatility and $d_2$ is the standard argument of the [Black formula](api/options/black.md#quantflow.options.bs.black_price).
+where $K$ is the strike, $F$ is the Forward price, $\tau$ is the [time to maturity](#time-to-maturity-ttm), $\sigma$ is the implied Black volatility and $d_2$ is the standard argument of the [Black formula](api/options/black.md#quantflow.options.bs.black_price).
 
 Unlike the [vol-adjusted moneyness](#moneyness-vol-adjusted), which is centered at the forward, this measure is zero at the median of the risk-neutral distribution, $K = F e^{-\sigma^2\tau/2}$.
 
@@ -189,7 +189,7 @@ The vol-adjusted moneyness is used in the context of option pricing in order to
     m_\sigma = \frac{1}{\sigma\sqrt{\tau}}\ln\frac{K}{F} = \frac{m}{\sigma}
 \end{equation}
 
-where $K$ is the strike, $F$ is the Forward price, $\tau$ is the time to maturity, $\sigma$ is the implied Black volatility and $m$ is the [moneyness](#moneyness).
+where $K$ is the strike, $F$ is the Forward price, $\tau$ is the [time to maturity](#time-to-maturity-ttm), $\sigma$ is the implied Black volatility and $m$ is the [moneyness](#moneyness).
 
 ## Parseval's Theorem
 
@@ -221,7 +221,7 @@ The [probability density function](https://en.wikipedia.org/wiki/Probability_den
 ## Put-Call Parity
 
 Put-call parity is a no-arbitrage relationship between the prices of European call
-and put options with the same strike $K$ and time to maturity.
+and put options with the same strike $K$ and [time to maturity](#time-to-maturity-ttm).
 
 \begin{equation}
     C - P = D_q \left(F - K\right)
@@ -231,9 +231,16 @@ where $D_q$ is the [discount factor](#discount-factor) of the quoting asset (gen
 at maturity and $F$ is the forward price
 of the underlying asset at maturity.
 
-Denoting forward-space prices
-$c = C/(D_q\ F)$ and $p = P/(D_q\ F)$ (see [Black Pricing](api/options/black.md)), the relationship
-reads:
+Denoting forward-space prices for calls and puts as:
+
+\begin{equation}
+\begin{aligned}
+    c &= \frac{C}{D_q\ F} \\
+    p &= \frac{P}{D_q\ F}
+\end{aligned}
+\end{equation}
+
+see [Black Pricing](api/options/black.md), the relationship reads:
 
 \begin{equation}
     c - p = 1 - \frac{K}{F} = 1 - e^k
diff --git a/docs/tutorials/volatility_surface.md b/docs/tutorials/volatility_surface.md
index 2249623b..2309062b 100644
--- a/docs/tutorials/volatility_surface.md
+++ b/docs/tutorials/volatility_surface.md
@@ -101,13 +101,21 @@ surface2 = surface_from_inputs(inputs)    # VolSurfaceInputs -> VolSurface
 ## Extracting Forwards and Discount Factors
 
 Pricing an option requires two market inputs beyond the option price itself: the forward
-price $F$ of the underlying at expiry, and the discount factor $D$ for that maturity.
+price $F$ of the underlying at expiry, and the quote discount factor $D_q$ for that
+maturity, where the quote currency is usually USD.
 
 In liquid markets these quantities are directly observable. Futures and forward contracts
-give $F$ outright, and interest rate swaps or government bond strips give $D$. In many
-option markets, however, neither is quoted directly. Crypto options on Deribit are a
-clear example: there is no liquid term structure of interest rates and the forward for
-each expiry must be inferred from the options themselves.
+give $F$ outright, and interest rate swaps or government bond strips give $D_q$. In many
+option markets, however, neither is quoted directly.
+
+!!! note "Deribit Forward"
+
+    Crypto options on Deribit are a clear example. There is no liquid term structure
+    of interest rates, and while Deribit quotes futures for each expiry, they are
+    often illiquid, with wide bid-ask spreads and stale or outright wrong prices.
+
+    The forward for each expiry must therefore be inferred from the options
+    themselves.
 
 Even when forwards are available, the discount factor used to value options may differ
 from the rate implied by the forward-spot basis. For equity options the carry includes
@@ -115,10 +123,40 @@ dividends and repo costs that are not captured by a simple interest rate curve.
 crypto inverse options the discount factor reflects funding in the underlying asset
 rather than in dollars.
 
-For these reasons, quantflow can extract $D_q$ and $D_a$ directly from the market prices
-of options using put-call parity. The
+For these reasons, quantflow extracts $D_q$ and $D_a$ directly from the market prices
+of options using [put-call parity](../glossary.md#put-call-parity).
+
+### Put-call parity and the implied forward
+
+For each maturity, the parity relationship is fitted in the normalized form:
+
+\begin{equation}
+\frac{C - P}{S} = D_a - D_q \frac{K}{S}
+\end{equation}
+
+where $S$ is the spot price and $D_a$ the asset discount factor. The same equation
+holds for inverse options with the left hand side replaced by $c - p$, the price
+difference in units of the underlying.
+
+The price difference is linear in the strike, so a regression across strikes
+identifies $D_a$ and $D_q$, and the line crosses zero exactly at the forward:
+
+\begin{equation}
+F = S \frac{D_a}{D_q}
+\end{equation}
+
+[put_call_parities][quantflow.options.surface.VolCrossSectionLoader.put_call_parities]
+collects the most liquid pairs at each maturity, ranked by the bid-ask spread of the
+parity price, and
+[implied_forward][quantflow.options.parity.PutCallParities.implied_forward] fits the
+regression and returns the implied forward.
+
+### Discount curve calibration
+
+The
 [calibrate_curves][quantflow.options.surface.GenericVolSurfaceLoader.calibrate_curves]
-method supports three modes:
+method fits smooth yield curves to the same put-call parity data across all
+maturities. It supports three modes:
 
 - **Both curves**: pass a [YieldCurve][quantflow.rates.yield_curve.YieldCurve] type for
   both `quote_curve` and `asset_curve`. A single OLS regression per maturity identifies
diff --git a/quantflow/data/yahoo.py b/quantflow/data/yahoo.py
index 43d90591..36f54a63 100644
--- a/quantflow/data/yahoo.py
+++ b/quantflow/data/yahoo.py
@@ -132,8 +132,15 @@ def loader_from_chain(
         US equity options are non-inverse: prices are in the quote currency and
         the spot is taken from the underlying quote. Forwards are not provided
         by Yahoo, so they are recovered from put-call parity by the loader.
+
+        When ref_date is None and the underlying quote carries a
+        regularMarketTime entry, that time is used as the reference date for
+        the yield curves, falling back to the current time otherwise.
         """
         symbol = chain.get("underlyingSymbol", "")
+        quote = chain.get("quote") or {}
+        if ref_date is None and (market_time := quote.get("regularMarketTime")):
+            ref_date = datetime.fromtimestamp(market_time, tz=timezone.utc)
         ref = ref_date or utcnow()
         loader = VolSurfaceLoader(
             asset=symbol,
@@ -144,7 +151,6 @@ def loader_from_chain(
             quote_curve=NoDiscountCurve(ref_date=ref),
             asset_curve=NoDiscountCurve(ref_date=ref),
         )
-        quote = chain.get("quote") or {}
         bid = quote.get("bid") or quote.get("regularMarketPrice")
         ask = quote.get("ask") or quote.get("regularMarketPrice")
         if bid and ask:
diff --git a/quantflow/options/parity.py b/quantflow/options/parity.py
index aef8a107..b320853a 100644
--- a/quantflow/options/parity.py
+++ b/quantflow/options/parity.py
@@ -20,8 +20,9 @@ class DiscountPair(BaseModel, frozen=True):
 
 
 class PutCallParity(BaseModel, frozen=True):
-    """A matched put-call parity at a single strike,
-    used for discount curve calibration."""
+    """A [put-call parity](../../glossary.md#put-call-parity) at a single strike
+
+    used for forward and discount curve calibration."""
 
     strike: Decimal = Field(description="Strike price")
     call: Price = Field(description="Call option bid/ask prices")
@@ -91,10 +92,15 @@ def fit_discounts(
         min_rate_q: float = 0.0,
         min_rate_a: float = 0.0,
     ) -> DiscountPair | None:
-        """Return the fitted discount factors, or None if the result is invalid.
+        r"""Return the fitted discount factors, or None if the result is invalid.
 
         Both direct and inverse options satisfy the same normalized equation
-        y = Da - (Dq/S) * K, where y = mid/S for direct and y = mid for inverse.
+
+        \begin{equation}
+            y = Da - K \frac{Dq}{S}
+        \end{equation}
+
+        where y = mid/S for direct and y = mid for inverse.
 
         When both known values are None a full OLS is run via constrained least squares.
         When one is provided the other is solved analytically as the mean over pairs.
diff --git a/quantflow/options/surface.py b/quantflow/options/surface.py
index aad02aea..80ceef5d 100644
--- a/quantflow/options/surface.py
+++ b/quantflow/options/surface.py
@@ -1441,9 +1441,10 @@ def calibrate_spot(
         """Calibrate the spot price from short-dated put-call parity.
 
         For short-dated options where discount factors are approximately 1,
-        put-call parity simplifies to C - P = S - K, so S = C - P + K.
+        put-call parity simplifies to `C - P = S - K`, so `S = C - P + K`.
+
         This method computes the median implied spot across all put-call pairs
-        with time to maturity at or below max_ttm and updates the spot price.
+        with time to maturity at or below `max_ttm` and updates the spot price.
 
         Returns the implied spot, or None if no maturities fall within max_ttm.
         """