reletter-python

Official Python client for the Reletter newsletter API. Search 6M+ email newsletters across Substack, LinkedIn, Ghost, and more. Fetch metadata and contacts, pull issue text, and build alerts and pipelines.

Thin, typed wrapper around the Reletter HTTP API. Ships with a reletter CLI for shell scripts and AI coding agents. If you want Reletter inside an AI assistant via Model Context Protocol, use the Reletter MCP Server.

What you can build with it

• Find newsletters to contact about getting your product, tool, or book featured — filter by audience size, topic, or platform, then pull verified contact emails in one pass
• Build sponsorship, cross-promotion, and PR target lists, then export contacts to your CRM
• Enrich a CRM with newsletter metadata, subscriber numbers, and contacts
• Monitor brand or keyword mentions by polling search.issues with a rolling threshold
• Pull subscriber numbers, engagement, language, country, and rankings for any newsletter
• Grab daily Substack / LinkedIn / Reletter chart data
• Feed full newsletter issue text into your own LLM pipeline
• Power a newsletter discovery app: search, autocomplete, similar newsletters

Install

pip install reletter            # SDK (and CLI)
pipx install reletter           # CLI in an isolated venv (recommended for the CLI)

Python 3.8+.

Command line

pip install reletter also installs a reletter command. Every method on the Python client has a CLI equivalent. Authentication is via RELETTER_API_KEY in the environment. Output is JSON on stdout, structured errors on stderr.

export RELETTER_API_KEY=your_api_key

# Look up a publication
reletter publications get doomberg | jq '.publication.name'

# Search with Stripe-style filters
reletter search publications \
  --query "climate" \
  --filters '{"subscribers":{"gte":5000},"active":true}'

# Search newsletter issues for the last 7 days
reletter search issues --query "openai" --threshold 604800

# Check your quota
reletter account quota

Exit codes: 0 success, 1 API or network error, 2 usage error (bad flags), 4 authentication error, 5 server error (5xx).

Run reletter --help for the full command tree, or reletter <group> --help (e.g. reletter publications --help) for commands inside a group. The seven groups match the Python client: search, publications, issues, contacts, charts, common, account.

Python quickstart

Grab an API key from reletter.com/developers.

from reletter import Reletter

client = Reletter(api_key="your_api_key")

# Look up a publication by its Reletter slug
publication = client.publications.get("doomberg")
print(publication["publication"]["name"], publication["publication"]["subscribers"])

# Search for newsletters with filters
results = client.search.publications(
    query="artificial intelligence",
    filters={"subscribers": {"gte": 5000}, "active": True},
    per_page=25,
)
for p in results["publications"]:
    print(p["id"], p["name"])

# Auto-paginate
for p in client.search.iter_publications(query="climate", limit=200):
    print(p["id"])

# Pull contacts
contacts = client.contacts.get("doomberg")
for c in contacts["contacts"]["email"]:
    print(c["email"], c["verification_status"])

The client also picks up RELETTER_API_KEY from the environment:

import os
os.environ["RELETTER_API_KEY"] = "your_api_key"

from reletter import Reletter
client = Reletter()

Async

import asyncio
from reletter import AsyncReletter

async def main():
    async with AsyncReletter() as client:
        publication = await client.publications.get("doomberg")
        async for p in client.search.iter_publications(query="ai", limit=100):
            print(p["name"])

asyncio.run(main())

Filters

Search endpoints accept Stripe-style filter dicts, raw DSL strings, or lists of clauses:

# Dict (preferred)
client.search.publications(filters={"subscribers": {"gte": 10000}, "active": True})

# Raw DSL string
client.search.publications(filters="subscribers:gte:10000,active:is:true")

# List of raw clauses
client.search.publications(filters=["subscribers:gte:10000", "active:is:true"])

See https://reletter.com/developers for the available fields and operators.

Errors

from reletter import (
    Reletter,
    AuthenticationError,
    BadRequestError,
    RateLimitError,
)

try:
    client = Reletter()
    client.publications.get("doomberg")
except AuthenticationError:
    ...   # invalid / missing API key
except RateLimitError:
    ...   # 429 — back off and retry
except BadRequestError as e:
    print(e.message, e.body)

The client retries automatically on 429 and 5xx responses (default 2 retries, exponential backoff). Configure with Reletter(max_retries=N) or 0 to disable.

License

MIT. Copyright Reletter.