# Illegal Metacharacter in Parameter Name in Json Data

**URL:** <https://community.f5.com/t/illegal-metacharacter-in-parameter-name-in-json-data/76776>\
**Category:** Technical Forums\
**Tags:** security, cloud, application-delivery\
**Created:** [December 18, 2025, 12:23pm UTC](https://community.f5.com/t/illegal-metacharacter-in-parameter-name-in-json-data/76776 "2025-12-18T12:23:08Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![SRM](https://avatars.discourse-cdn.com/v4/letter/s/a87d85/32.png) [@SRM](https://community.f5.com/u/SRM)\
**Post date:** [December 18, 2025, 12:23pm UTC](https://community.f5.com/t/illegal-metacharacter-in-parameter-name-in-json-data/76776/1 "2025-12-18T12:23:08Z")

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Dears,&nbsp;  
Can someone tell what is the issue here as the BIG-IP is reporting the illegal metacharacter “#” in parameter name but the highlighted part of the violation doesnt contain metacharacter # in the first place and the parameter which BIG-IP displayed in the highlighted part is actually not a parameter. I believe the issue is with the BIG-IP only. Any suggestions here, please? I think issue is that BIG-IP is not paring the Json payload properly

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**Author:** ![Juergen\_Mang](https://d1p9zq3aats0t8.cloudfront.net/user_avatar/community.f5.com/juergen_mang/32/12756_2.png) [@Juergen\_Mang](https://community.f5.com/u/Juergen_Mang)\
**Post date:** [December 18, 2025, 8:43pm UTC](https://community.f5.com/t/illegal-metacharacter-in-parameter-name-in-json-data/76776/2 "2025-12-18T20:43:20Z")

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If “Parse as parameters” is checked, each JSON key is treated as parameter name. You can disable this checkbox or configure the parameter name metachars accordingly.

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**Author:** ![SRM](https://avatars.discourse-cdn.com/v4/letter/s/a87d85/32.png) [@SRM](https://community.f5.com/u/SRM)\
**Post date:** [December 19, 2025, 7:37am UTC](https://community.f5.com/t/illegal-metacharacter-in-parameter-name-in-json-data/76776/3 "2025-12-19T07:37:30Z")

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Dear Juergen,

Thanks for your response. Yes, it’s true that “Parse as parameters” is checked, but my question is why the highlighted part is considered a single parameter when it contains almost 12 to 13 JSON keys and their values

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**Author:** ![NicolasDupin](https://avatars.discourse-cdn.com/v4/letter/n/f07891/32.png) [@NicolasDupin](https://community.f5.com/u/NicolasDupin)\
**Post date:** [December 19, 2025, 10:22am UTC](https://community.f5.com/t/illegal-metacharacter-in-parameter-name-in-json-data/76776/4 "2025-12-19T10:22:54Z")

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How is your json profile used ?

I will be curious to see your “Header-Based Content Profiles” tab.

It might be that your profile is just, not applied (and then doesn’t parse the json correctly) ?

I would also be interresting to see your violation with the detailed tab (you only displayed the request data). But it is strange that it states “#”