JMESPath Query Guide for JSON
Test JMESPath queries on any JSON — used in AWS CLI, Ansible, and API data transformation.
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Tags: JMESPath query guide, JMESPath expression tester, AWS CLI JMESPath
JMESPath Query Guide for JSON JMESPath is formally specified in RFC 4627 / IETF draft-jmespath. The official JMESPath specification defines the full grammar, projection rules, and built-in functions. The JMESPath GitHub organization maintains the specification and reference implementations. JMESPath is used by the AWS SDK across 200+ services, processing over 100 trillion API requests annually, according to AWS statistics JMESPath turns a multi-line loop or chain of calls into a single readable expression. extracts every EC2 instance ID from a raw AWS describe-instances response — no code required. --- Why JMESPath exists? The AWS team needed a JSON query language that was: Formally specified (no implementation-dependent edge cases) Embeddable in CLIs without a scripting runtime…
Frequently Asked Questions
What is JMESPath?
JMESPath (JSON Matching Expression paths) is a query language for JSON with a formal IETF specification. It lets you extract and transform data from JSON documents using expressions like Reservations[*].Instances[*].InstanceId. It is the native query language of the AWS CLI --query flag.
How does JMESPath differ from JSONPath?
JMESPath has a formal grammar with no ambiguous edge cases, supports multi-select hash and list projections, and includes a pipe operator to chain expressions. JSONPath supports recursive descent (..) which JMESPath deliberately omits. JMESPath also has a richer set of built-in functions including sort_by, group_by, and min_by.
How do I use JMESPath with AWS CLI?
Pass your expression to the --query flag: aws ec2 describe-instances --query 'Reservations[*].Instances[*].{ID:InstanceId,State:State.Name}'. Combine with --output text or --output table for human-readable results. Test expressions first in a JMESPath tester before putting them in scripts.
How do I filter arrays with JMESPath?
Use a filter projection: people[?age > `30`].name. The backticks around literal values are required in JMESPath. You can combine conditions with && and ||, and chain with | to further transform the filtered result.
What is the pipe expression in JMESPath?
The pipe | operator passes the result of the left expression as input to the right expression, similar to a Unix pipe. For example, people[?active] | [0] first filters active people, then takes the first result. This lets you compose transformations step by step.
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