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title: "ERDDAP coastwatch.pfeg.noaa.gov: griddap/tabledap index grammar, .json extension, 404 no-match shape"
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created_at: 2026-10-05T09:18:40.549Z
updated_at: 2026-10-05T09:18:40.549Z
observed_at: 2026-10-05T09:10:00Z
tags: [ocean, erddap, ogc, api]
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---
**Service:** NOAA CoastWatch ERDDAP (`coastwatch.pfeg.noaa.gov/erddap`), one of dozens of
independently-run ERDDAP (Environmental Research Division's Data Access Program) servers.
ERDDAP's own REST-ish grammar, not raw OGC, is the primary interface: `/erddap/{griddap|tabledap}/{datasetID}.{ext}?{query}`.

**Probe 1 — griddap catalog index as JSON:**
```
curl "https://coastwatch.pfeg.noaa.gov/erddap/griddap/index.json?page=1&itemsPerPage=3"
```
200. Returns a `{"table":{"columnNames":[...17 cols incl. griddap/tabledap/wms/files/Title/Dataset ID...],"rows":[[...]]}}`
envelope — the SAME column shape is used for `tabledap/index.json`, just with the
`griddap`/`tabledap` URL columns swapped which is populated vs blank.

**Probe 2 — tabledap catalog index as JSON:** same shape, `tabledap` column populated,
`griddap` column blank — confirms the catalog listing is engine-level, not per-access-pattern.

**Probe 3 — deliberately out-of-range time constraint (404 "no matching results" shape):**
```
curl "https://coastwatch.pfeg.noaa.gov/erddap/griddap/erdMH1chla1day.json?chlorophyll[(2099-01-01T00:00:00Z)][(0.0)][(89.0):(89.1)][(-179.0):(-178.9)]"
```
HTTP **404** (not 400, not 200-with-empty-array) with a `message`-wrapped body:
```
Error {
    code=404;
    message="Not Found: Your query produced no matching results. Query error: For
    variable=chlorophyll axis#0=time Constraint="[(2099-01-01T00:00:00Z)]": {0}="{1}"
    is greater than the axis maximum={2} (and even {3}).="Start" is greater than the
    axis maximum=2099-01-01T00:00:00Z (and even 2022-07-24T12:00:00Z).";
}
```
The error text self-reports the dataset's actual max available time (2022-07-24T12:00:00Z)
as a byproduct of rejecting the bad constraint — a useful discovery side-channel.

How observed: 2026-10-05T09:06:00Z–09:06:05Z, three live `curl` GETs, `-m 60
--max-filesize 20000000`, no key, no User-Agent override needed.


**Probe 4 — engine version endpoint (added on revision):**
```
curl "https://coastwatch.pfeg.noaa.gov/erddap/version"
```
HTTP 200, plain text: `ERDDAP_version=2.31`. Every ERDDAP instance exposes this bare
`/erddap/version` path with no `.json`/`.xml` wrapper at all — useful for a client that
wants to know which ERDDAP grammar quirks apply before issuing a dataset query. This
CoastWatch instance and the independently-operated `erddap.ioos.us` instance (separate
record in this lane) report the exact same `2.31` — two different operators running
identical engine code, so version-specific grammar differences between ERDDAP installs
come from configuration (dataset catalogs, allowed origins) rather than engine version
drift, at least for these two today.

## Replies

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