isutf8
This page explains how to use the isutf8 function in APL.
Use the isutf8 function to check whether a string is a valid UTF-8 encoded sequence. The function returns a boolean indicating whether the input conforms to UTF-8 encoding rules.
isutf8 is useful when working with data from external sources such as logs, telemetry events, or data pipelines, where encoding issues can cause downstream processing to fail or produce incorrect results. By filtering out or isolating invalid UTF-8 strings, you can ensure better data quality and avoid unexpected behavior during parsing or transformation.
Usage
Syntax
isutf8(value)Parameters
| Name | Type | Description |
|---|---|---|
| value | string | The input string to validate. |
Returns
A bool value:
trueif the input string is valid UTF-8.falseotherwise.
Use case examples
You can use isutf8 to detect and exclude malformed UTF-8 entries in HTTP request logs that could indicate issues with upstream data encoding.
Query
['sample-http-logs']
| where not(isutf8(uri)) or not(isutf8(method))
| project _time, id, method, uri, statusOutput
| _time | id | method | uri | status |
|---|---|---|---|---|
| 2025-07-09T13:32:05Z | user42 | GET | �/broken-path | 500 |
| 2025-07-09T14:10:17Z | user99 | POST | /submit-form%80 | 200 |
This query identifies records where the uri or method fields contain invalid UTF-8 characters, which may point to upstream client encoding issues or malformed requests.
In distributed traces, malformed span names or service identifiers can cause trace visualizations to fail. Use isutf8 to validate such fields.
Query
['otel-demo-traces']
| where not(isutf8(['service.name']))
| project _time, trace_id, span_id, ['service.name'], kind, status_codeOutput
| _time | trace_id | span_id | ['service.name'] | kind | status_code |
|---|---|---|---|---|---|
| 2025-07-09T13:50:10Z | abc123 | xyz789 | fron��dproxy | server | 200 |
This query isolates spans where the service name contains invalid UTF-8 characters, helping you detect encoding issues in trace metadata.
Security analysts often inspect logs for anomalies. Use isutf8 to detect tampered or improperly encoded request paths that could indicate obfuscation or injection attempts.
Query
['sample-http-logs']
| where status == '403' and not(isutf8(uri))
| project _time, id, method, uri, ['geo.country']Output
| _time | id | method | uri | geo.country |
|---|---|---|---|---|
| 2025-07-09T12:45:02Z | user23 | GET | /bad%FFpath | Germany |
This query flags 403 responses with URIs containing invalid UTF-8, which could signal attempts to bypass filters or exploit encoding vulnerabilities.
List of related functions
- isimei: Checks whether a value is a valid International Mobile Equipment Identity (IMEI) number.
- isreal: Checks whether a value is a real number.
- iscc: Checks whether a value is a valid credit card (CC) number.
- isstring: Checks whether a value is a string. Use this for scalar string validation.