RRDtool is the open-source standard for high-performance time-series logging and graphing. It stores round-robin databases efficiently and ships bindings-friendly tooling for shell, Perl, Python, Ruby, and other environments.
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RRDtool pricing questions
Is RRDtool free?
Yes. RRDtool has an ongoing free plan. RRDtool is open-source software distributed from the official project site without commercial subscription checkout.
How much does RRDtool cost?
RRDtool is listed as free. No paid plan with a published price was found.
Does RRDtool have an API?
API or developer access is mentioned. Documentation on the project site covers command-line and library APIs for logging and graphing time-series data.