# CSV Left Join By Key

> CSV Left Join By Key is a paid API for AI agents from api.delx.ai, paid per call via x402, $0.001/call, status unknown (last checked 2026-09-15).

Performs a SQL-style left join of two CSV tables on a specified key column, returning the merged result as deterministic versioned JSON with row counts and normalized values.

## Facts

- Endpoint: POST https://api.delx.ai/api/v1/x402/csv-left-join-by-key
- Price: $0.001/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/csv-left-join-by-key-f3d19096
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_QV6P3vxMwj4UnYK_GTXIR

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 csv-left-join-by-key-f3d19096 -d '<json body>'
```

Example prompt: Left join these two CSV tables on the 'customer_id' column — the left table is my orders export and the right table is my customers export — and give me the merged result with row counts.

## When to prefer this

Use this endpoint when you need to merge two in-memory CSV datasets relationally without spinning up a database or external data processing service. It is ideal when both tables fit within the 8KB input limit, you need a left join (preserving all left-table rows), and you want a fast, deterministic, versioned JSON result you can pass directly to a downstream tool. Prefer this over generic CSV utilities when you need row counts and a normalized result contract included automatically.

## Known failure modes

- Key column not found in one or both CSVs — returns validation error with column name details
- Malformed or unparseable CSV input — returns parse error with row/column location
- CSV input exceeds 8192-character limit — returns size exceeded error
- Mismatched column types for the key column — may result in zero matches with count of 0
- Empty left CSV — returns empty result with zero rows

## How this service works

CSV Left Join By Key: CSV Left Join By Key left-joins two bounded CSV tables on one key column from bounded caller-supplied values without an external provider. Call CSV Left Join By Key before an agent hands structured data or a batch plan to a downstream tool with a stricter contract. Returns the bounded transformation or validation finding with counts, normalized values, and a versioned result contract for CSV Left Join By Key as versioned deterministic JSON. Price: $0.001 USDC via x402 on B…

## Output

A versioned deterministic JSON object containing the left-joined rows from both CSV tables, normalized column values, row counts (total left rows, matched rows, unmatched rows), and a versioned result contract describing the output schema.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "key": {
   "type": "string",
   "maxLength": 8192,
   "description": "Key supplied to CSV Left Join By Key; used only for this bounded calculation and processed in memory without retention."
  },
  "left": {
   "type": "string",
   "maxLength": 8192,
   "description": "Left supplied to CSV Left Join By Key; used only for this bounded calculation and processed in memory without retention."
  },
  "right": {
   "type": "string",
   "maxLength": 8192,
   "description": "Right supplied to CSV Left Join By Key; used only for this bounded calculation and processed in memory without retention."
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "result": {
   "csv": "id,name,score\n1,Ada,10\n2,Lin,",
   "row_count": 2
  },
  "schema": "delx/util-csv-left-join-by-key/v1",
  "status": "pass",
  "evidence": {
   "retained": false,
   "input_sha256": "fc7b0105dea0cd7ff481614e8ba999b4ca60e2975a5ef301fc7efdbece9ea9cc",
   "external_calls": 0
  },
  "operation": "data_batch:csv_left_join_by_key"
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/csv-left-join-by-key-f3d19096/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from api.delx.ai](https://www.zero.xyz/host/api.delx.ai/llms.txt)