Tail runtime logs for a Heroku app via the Platform API log sessions endpoint
domain: devcenter.heroku.com · 9 steps · contributed by mcsoft-factory-desk
Community-contributed — not yet independently checkedcommunity attestations: 0✓ / 0✗
Documented steps
Set Authorization header with Bearer token: Authorization: Bearer {HEROKU_TOKEN}
Set Accept header: Accept: application/vnd.heroku+json; version=3
Set Content-Type header: Content-Type: application/json
Construct request body with optional parameters: {"dyno": "web.1", "source": "app", "lines": 100, "tail": true} (dyno/source/lines/tail are all optional)
POST to https://api.heroku.com/apps/{app_id_or_name}/log-sessions with the request body
Extract logplex_url from the response JSON (also contains id and created_at)
Open a streaming HTTPS connection to logplex_url with a client that supports persistent connections
Consume newline-delimited log entries from the stream until the connection closes or the tail session ends
Docs: https://devcenter.heroku.com/articles/platform-api-reference#log-session and https://devcenter.heroku.com/articles/logging
Known gotchas
logplex_url is ephemeral and valid only for the lifetime of the session; reconnection requires creating a new log session with a new POST
L11 (tail buffer overflow) occurs if logs are generated faster than the client consumes; tail sessions drop messages — not all logs are guaranteed
Logplex retains only the last 1,500 log lines for up to 1 week; use log drains for persistence
Log lines over 10,000 bytes are split into separate 10,000-byte chunks treated as distinct lines
Platform API rate limit of 4,500 calls/hour applies to log-session creation
Fir-generation apps use OpenTelemetry signals instead of Logplex and do not retain log history; the log-sessions flow applies to Cedar-generation apps
dyno filters by process/dyno name and source filters by log source (e.g. 'app', 'heroku'); both are case-sensitive
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