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The Logs page provides several filters that let you narrow down your API activity to exactly the requests you care about. All filters are applied together — if you set both an API key filter and a status filter, you’ll only see requests that match both.

Try it in the app

Follow an interactive walkthrough of this guide inside Lettr.

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Date Range

The date range picker controls which time window Lettr queries for log data. By default it covers the last 7 days. You can extend it up to 30 days into the past — this is the maximum retention period for API logs. Dates beyond that are no longer available. The picker includes both a start and end date, as well as start and end times. Your local time is converted to UTC before the query runs, so you don’t need to think about timezone conversion yourself.

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API Key

If your account has multiple API keys, this filter lets you isolate requests made with a specific key. This is particularly useful when you have separate keys for different environments (staging vs. production) or different services. Select All API Keys to see everything, or choose a specific key from the dropdown.

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User Agent

Lettr automatically detects the client type based on the user agent string in each request and groups them into recognizable categories. The available options are: Selecting Other is useful when you’re trying to identify unexpected traffic sources on your account.

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HTTP Status Code

Filter by the response status code to focus on successes or errors: Filtering by 4xx or 5xx status codes is the fastest way to find failed requests when debugging an integration.

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Pagination

Log results are paginated using cursor-based navigation. The footer of the table shows how many requests are displayed on the current page, along with Previous and Next buttons. Cursor-based pagination means the results are always consistent — new log entries appearing in real time won’t cause items to shift between pages as you navigate. When you apply or change any filter, pagination resets to the first page automatically.

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Inspecting a Log Entry

Click the info icon on any row to open the detail dialog. This shows:
  • The full Request Body — the exact JSON payload your application sent. This is where you can verify that fields like from, to, subject, html, and options are structured correctly.
  • The full Response Body — exactly what Lettr returned. For successful requests this includes the request_id and other confirmation data. For errors, it includes the error code and message.
  • The IP Address and User Agent string, along with the API Key name and prefix.
If you’re debugging a specific email send that failed, start by filtering Logs by the date and time you attempted the send, then look for a POST request to /api/emails. The detail dialog will show you exactly what went wrong in the response.

API Logs Overview

What logs capture and when to use them

Rate Limits

Understanding and handling 429 responses

Errors and Retries

How to handle common API errors

API Keys

Managing and securing the keys shown in your logs