can i add dynamic variables in the Custom Headers (Optional)? | ElevenLabs | Page 1

short cryptBOT Sep 1, 2025, 9:13 AM

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AI-generated Answer for johnnyflaco

Yes. In server/webhook tools you can set Custom Headers to use dynamic variables. Use the {{ variable_name }} syntax in the header value (e.g., Authorization: Bearer {{secret__api_token}}). Dynamic variables can be used in tool parameters and headers, and you pass their values at runtime. For sensitive values, prefix the variable with secret__; secret dynamic variables are only usable in webhook tool headers and are never sent to the LLM. (elevenlabs.io)

Sources:
Dynamic variables | ElevenLabs Documentation

junior spindle Sep 1, 2025, 9:16 AM

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{{system__caller_id}} in the header custom value or just ? system__caller_id?

short cryptBOT Sep 1, 2025, 9:16 AM

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AI-generated Answer for johnnyflaco

Use double curly braces: {{system__caller_id}}.

Details:

Tool/webhook headers support dynamic variables, so {{system__caller_id}} will be resolved at call time. You can also use secret dynamic variables (prefix secret__) in webhook tool headers. (elevenlabs.io)
SIP Trunking “Add custom headers (optional)” is documented for static SIP headers; there’s no doc indicating dynamic-variable interpolation there. Treat those as literal values. (elevenlabs.io)

If you’re setting headers on a server/webhook tool, use {{system__caller_id}}. If you’re setting headers on a SIP Trunking number, don’t expect variables to resolve.

Sources:
May 19, 2025 | ElevenLabs Documentation
SIP trunking | ElevenLabs Documentation

junior spindle Sep 1, 2025, 9:18 AM

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yeah its on a sip trunking number though

short cryptBOT Sep 1, 2025, 9:18 AM

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AI-generated Answer for johnnyflaco

Short answer: For SIP trunking numbers, the “Custom headers (optional)” field is not documented to support dynamic-variable templating. Treat those SIP headers as static strings. The {{system__caller_id}} syntax is supported for tool/webhook headers (not SIP trunk headers), and is the correct form when used there. (elevenlabs.io)

What the docs say:

SIP trunking: You can add provider-specific custom SIP headers, but the page does not state that dynamic variables can be interpolated in those values. Caller/call IDs should be provided by your SIP INVITE (e.g., From, and optionally X-CALLER-ID/X-CALL-ID). Once received, ElevenLabs exposes caller_id as a system dynamic variable for use downstream. (elevenlabs.io)
Dynamic variables: system__caller_id is a built-in variable. Dynamic variables can be used in prompts, tool parameters, and tool headers using double curly braces, e.g., {{system__caller_id}}. (elevenlabs.io)
Changelog: “Dynamic variables in headers” was added for tools (i.e., webhook headers), confirming support there. (elevenlabs.io)

Practical guidance:

For SIP trunk “Custom headers”: use literal values required by your carrier (no templating). (elevenlabs.io)
To pass the caller ID from that SIP call to your downstream API/tool, reference it in the tool header value as {{system__caller_id}}. (elevenlabs.io)

If you need templated SIP headers specifically, there’s no official documentation confirming that capability today. (elevenlabs.io)

junior spindle Sep 1, 2025, 9:19 AM

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How to also keep caller id from the customer when using conference transfer btw?

#can i add dynamic variables in the Custom Headers (Optional)?