readOnlyHint
readOnlyHint is an MCP tool annotation that, when true, says the tool only reads and does not change anything in its environment. It is the most used annotation in our MCP dataset (the 425 open servers we track across every store, not only the 105 behind ChatGPT and Claude listings, with 7,777 tools): 91% of its tools set it on October 13, 2026, and 66% set it to true.
- Tools that set it
- 91%
- Set to true
- 66%
- Servers using it
- 378 of 425MCP dataset, every store we track
- Default
- false
More from our data
378 of the 425 open servers use it on at least one tool.
When readOnlyHint is true, destructiveHint and idempotentHint have no meaning: a tool that changes nothing can't be destructive, and calling it twice has no extra effect anyway.