CourtListener for empirical legal research

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Free Law Project's corpus. Three access routes with very different properties, and one distinction that people get wrong before they start.

The two corpora are not the same thing

corpus	source	coverage	contains
Opinions (case law)	scraped from court websites	federal and state	written decisions, full text
RECAP	PACER	federal only	docket entries, motions, filings

The tell is on the court record itself: pacer_court_id: null + has_opinion_scraper: true means a scraped state court, not a PACER one. Verified on Delaware Chancery:

GET /api/rest/v4/courts/delch/
  "full_name": "Court of Chancery of Delaware"
  "jurisdiction": "SA"            <- state
  "has_opinion_scraper": true
  "pacer_court_id": null          <- NOT RECAP

Pick the route before writing any code

route	auth	best for	cost
Bulk data files	none	any corpus-scale analysis	quarterly snapshot, big files
REST API v4	search/courts unauth; dockets needs a token	targeted queries, current data	rate-limited, polite pacing on you
DB replication / MCP	membership or commercial	continuous sync	contact FLP

Default to bulk for research. It is public domain, needs no account, and does not rate-limit you. Reach for the API only when you need data newer than the last quarterly snapshot, or when you want a few hundred records rather than a corpus.

Bulk data

No authentication. Public Domain Mark. Regenerated quarterly on the last day of March, June, September and December. Snapshots, not deltas — each file is the whole table.

https://com-courtlistener-storage.s3-us-west-2.amazonaws.com/?list-type=2&prefix=bulk-data/
aws s3 ls s3://com-courtlistener-storage/bulk-data/ --no-sign-request

Measured sizes, 2026-06-30 snapshot:

file	size	carries
opinions-YYYY-MM-DD.csv.bz2	54.6 GB	opinion full text
opinion-clusters-…	2.46 GB	court, date_filed, case name, docket_number
dockets-…	5.01 GB	docket metadata
courts-…	<10 MB	the court table
citation-map-…	0.52 GB	citation graph

Also published: financial disclosures, judges, oral arguments, and ~2 TB of ModernBERT opinion embeddings at s3://com-courtlistener-storage/embeddings/opinions/.

Filter clusters first, then stream opinions. opinion-clusters is 22× smaller and carries the court and date. Select the cluster ids you want, then stream-decompress the 54 GB opinions file and keep only matching rows. Never materialise the opinions CSV.

Files are PostgreSQL COPY TO output: CSV, UTF-8, header row. Schema dumps are published alongside; field definitions are in the CourtListener GitHub models.py, or via an OPTIONS request to the matching API endpoint.

REST API v4

https://www.courtlistener.com/api/rest/v4/

• search and courts work unauthenticated — 3,358 delch opinions were pulled in 206 unauthenticated calls.
• dockets returns {"detail":"Authentication credentials were not provided."} without a token.
• Token lives at /profile/api/ — which sits behind a "Let's confirm you are human" interstitial. That gate is the site's bot check and belongs to Free Law Project; the user clears it, not you.
• Search type params: type=o opinions, type=r RECAP dockets.

Pace politely and back off on 429/5xx. This is a nonprofit's free service; without a token there is no quota to raise, so courtesy is the entire budget.

API Facts

• suitNature is not normalised. The same NOS 160 appears as Stockholders Suits, 160 Contract: Stockholders Suits and 160 Stockholders Suits. Query the text (suitNature:"Stockholders Suits"), not the numeric code, or you silently lose most of the set.
• Derivative suits are docketed under more than one NOS. "shareholder derivative" returns 1,670 under NOS 160 and 2,020 under 850 (Securities/Commodities). Filtering to 160 alone drops more than half.
• docketNumber carries the C.A. number, which joins directly to a Delaware Chancery docket from Lex Machina or CourtConnect — measured at 100% match on 2,350 rows. That join is what lets a filing universe from one source meet a ruling from this one.
• Opinions are written decisions only, and that is a selection, not a gap. Measured against a verified Chancery filing universe: 82% of caption-derivative filings never produce a written opinion, because most dispositions are bench rulings from the transcript. An outcome variable built from opinions describes the selected fifth. Reporting a dismissal rate without that denominator is an unverified claim dressed as a finding.
• The bulk snapshot lags up to a quarter. The 2026-06-30 file lands two weeks after a 2026-06-15 event, so a study of anything recent gets a truncated post-period until the next drop. Check the snapshot date against your event date before designing the test.

Coverage and what is coming

Delaware Chancery: 3,358 opinions since 2012 (delch). Texas currently covers the Supreme Court, Court of Criminal Appeals and the 15 civil courts of appeal.

From the FLP wiki, verbatim:

"In 2026, we are collecting content from high and appellate courts at the five most populous states: California, New York, Texas, Florida, and Pennsylvania."

"In 2027 we aim to continue this with the Delaware Chancery Court and the next most populous states."

The 2027 item is filings, not opinions — Chancery opinions already exist. Docket-level state coverage would reach the bench rulings the opinion corpus structurally cannot see.

Red Flags — STOP if you catch yourself

About to	Why wrong	Do instead
Tell the user CourtListener is federal-only	True of RECAP, false of opinions — state case law is there	Check pacer_court_id / has_opinion_scraper on the court
Page the REST API for a corpus-scale pull	Rate-limited, slow, and rude to a nonprofit when the same data is a free download	Bulk files
Clear the human-verification interstitial to get a token	It is the site's bot check, and you are a bot	Ask the user; or use the unauthenticated endpoints, which cover most needs
Decompress the 54 GB opinions CSV to disk	You need a few thousand rows of it	Filter opinion-clusters first, then stream and match
Filter derivative suits on NOS 160 alone	2,020 of them are docketed 850	160 OR 850 plus a text filter, then hand-check
Report a dismissal rate from opinions without the selection denominator	82% of filings never get a written opinion; the rate describes the selected fifth	Quantify selection against a filing universe and lead with it
Assume the bulk snapshot is current	Quarterly, and the boundary may fall days after your event	Read the snapshot date; use the API for the tail

Related

• ui-json-capture — when the source is a paywalled UI rather than an open corpus
• wrds — the SEC-filing side of the same research questions