# US Court Opinions and Citations

> US Court Opinions and Citations is a paid API for AI agents from x402-filings.datalayer.workers.dev, paid per call via x402, $0.02/call, status unknown (last checked 2026-10-10).

Search US federal and state court opinions by party name, topic, or citation and retrieve case metadata including citation counts from CourtListener.

## Facts

- Endpoint: GET https://x402-filings.datalayer.workers.dev/v1/legal/court-cases?utm_source=zero.xyz
- Price: $0.02/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-10
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/us-court-opinions-and-citations-2515fa11
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_saXm_yW6Y2wXch_Q4Y4KY

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability us-court-opinions-and-citations-2515fa11
```

Example prompt: Can you search CourtListener for federal court opinions about antitrust filed after 2018, limited to the 9th Circuit, and tell me which ones have been cited the most by later cases?

## When to prefer this

Use this endpoint when you need to search US case law by topic, party name, or citation and want citation-count data to gauge precedential weight. Prefer it over generic legal search tools when you need structured metadata (docket number, court, jurisdiction, filing date) from CourtListener's database, especially for filtering by specific courts like SCOTUS or federal circuits and date ranges.

## Known failure modes

- Query term too vague returns low-relevance or no results
- Invalid court ID returns an error or empty result set
- Date filter excludes relevant older opinions when set too narrowly
- Limit capped at 50 — large result sets require pagination not supported by this endpoint
- Citation lookup by string may fail if citation format is non-standard

## How this service works

Search US federal and state court opinions from CourtListener. Query by party name, topic or citation and get the case name, court, jurisdiction, docket number, filing date, reporter citations and — the field that separates a landmark from a footnote — how many later opinions have cited it. Filter by court and filing date.

## Output

Returns a list of court opinions matching the query, each including the case name, court, jurisdiction, docket number, filing date, reporter citations, and a count of how many subsequent opinions have cited that case — enabling assessment of legal precedential weight.

## Request schema (JSON Schema)

```json
{
 "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"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "properties": {
      "q": {
       "type": "string",
       "examples": [
        "antitrust"
       ],
       "description": "Party name, topic or citation. Required."
      },
      "court": {
       "type": "string",
       "examples": [
        "ca9"
       ],
       "description": "Court id filter, e.g. ca9, scotus."
      },
      "limit": {
       "type": "integer",
       "examples": [
        20
       ],
       "description": "Max cases, 1-50. Default 20."
      },
      "filedAfter": {
       "type": "string",
       "examples": [
        "2020-01-01"
       ],
       "description": "Only opinions filed on or after, ISO date."
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object"
    }
   }
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/us-court-opinions-and-citations-2515fa11/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from x402-filings.datalayer.workers.dev](https://www.zero.xyz/host/x402-filings.datalayer.workers.dev/llms.txt)