Updated Aug 4, 2026

CEL Expression Editor

AutoTalk uses CEL (Common Expression Language) expressions in AI agents and workflows to make behaviour dynamic — personalising system messages with contact names, conditionally running steps, and computing values at runtime.

This page explains how to write and test CEL expressions using the built-in editor.

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Where expressions appear

CEL expressions appear wherever you see the CEL badge in the configuration UI:

• Agent → Messages tab — system message content (e.g. inject the contact's name into a prompt)
• Agent → Actions tab — the Condition field on each pre-action or post-action step
• Workflow → Steps — step conditions and output mappings

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The expression editor

When you open an action step for editing, the Condition field shows the compact expression editor. It has:

• Syntax highlighting — keywords, strings, and operators are colour-coded
• Real-time validation — a red error badge appears with the exact error message when the expression is invalid (the green Valid badge lives in the expanded workbench, not the compact field)
• Format button — auto-formats the expression (keyboard shortcut: Ctrl+Shift+F)
• Expand button — opens the full workbench (see below)

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Simple CEL vs raw CEL

System message fields (and other text fields) offer two authoring modes, toggled by the CEL button in the field header:

Mode	Example	When to use
Simple CEL (SCEL)	Hello {{contact.name}}!	Simpler syntax for text with variable substitutions
Raw CEL	"Hello " + contact.name + "!"	Full CEL syntax when you need logic, conditionals, or function calls

Both modes produce the same result. The {{variable}} syntax is automatically converted to raw CEL when you save.

Advanced field options

Expand the Advanced drawer under any expression field to configure:

Option	What it does
On failure	What happens if the expression throws an error at runtime: throw the error (throw, the default), return null, fall back to a string, or keep the original expression
Result type	Expected output type (any — the default — string, number, boolean, date, array, or object)
Fallback value	A literal string used as the result when On failure is set to Fallback to string

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The full workbench

Click Expand on any expression editor to open the full workbench in a dedicated view. Its toolbar has Explorer and Test toggle buttons that open a floating panel over the editor.

Explorer

The Explorer panel shows everything available in the current context:

• Variables tree — all variables you can reference in this expression, expandable to see nested fields. Click any variable or field to insert it at the cursor.
• Functions list — all built-in functions with their signature and description. Click to insert.
• Search box — filters both variables and functions as you type.

The variables shown depend on where the expression lives:

Location	Available variables
Agent pre-actions / post-actions	contact, contactMessage, conversation, company, step(0), step(1), …
Agent system messages	company, contact, contactMessage, conversation, and any tool results under context.tools.*
Workflow steps	_workflow, occurrenceDate, trigger inputs, step(0), …

Note: the contact is exposed as the contact variable — write contact.name in expressions. (Older builds labeled it client in the Explorer tree; the runtime key has always been contact.)

Test

The Test panel lets you evaluate the expression against custom variable values without touching a live conversation:

1. Edit the JSON on the left to define test values for variables (e.g. set contact.name to "Alice")
2. Click Run (or press Ctrl+Enter)
3. The result appears on the right — either the computed value or a formatted error message

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Variables reference

For a complete list of all available functions, see the CEL Functions Reference.

These variables are available inside agent expressions:

Variable	Description
contact	The contact who sent the message — contact.name, contact.contactIdentification, contact.tags, contact.customAttributes, etc.
contactMessage	The incoming message — contactMessage.body.text, contactMessage.type, etc.
conversation	The conversation session — conversation.contactId, conversation.lastMessageAt, conversation.isGroup, etc.
company	Your company profile — company.companyName, company.options, etc.
step(N)	Output of a previous step at index N — e.g. step(0).jwt, step(2).data[0], or get(step(1), 'executionContext.status')

There is no top-level employee variable in agent contexts. Fetch employee/professional data via a data step and read it from step(N).data[0].

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Common step outcome checks

Use the step helper functions for concise step status checks:

step_ok(0)                                          // true if step 0 completed successfully
step_data(0, "title")                               // get step 0's data.title
step_data(1, "choices.0.message.content", "")        // LLM response with fallback
step_error(2)                                        // {code, user_message, retryable} or null

Or use step(N).executionContext directly for lower-level checks:

get(step(0), 'executionContext.status') == 'completed'
get(step(1), 'executionContext.safeError.code') == 'unsupported_media_format'
get(step(2), 'executionContext.safeResult.reason') == 'condition_false'

safeError is intended for safe debugging and branching. It does not expose raw stack traces, secrets, or provider payloads.

See the CEL Functions Reference for the complete function list.

Debugging expression errors

When a CEL expression fails during a live conversation, an error bubble appears in the chat — visible only to your team, not to the contact.

Reading the error bubble

The collapsed bubble shows the error type and a one-line message. Click ▼ Expand to see the full detail panel.

Expanded view

The expanded panel has four sections:

Section	Content
CEL Expression	The exact expression that failed — copy it to paste into the workbench for testing
Metadata	Where the error happened: which section of the agent config, which message or action index
CEL Variables	(Debug log level only) The full list of variables and their values at the moment of the error
Full Payload	The raw error data as JSON

CEL Variables section

The CEL Variables section is the most useful for diagnosing problems:

• Use the filter box to search for the variable your expression references
• Expand any variable to inspect its actual value and structure
• Variables labelled truncated are large objects that were abbreviated

Note: CEL Variables only appears when the agent's Log level is set to Debug. Go to the agent's Options tab to raise the log level, then lower it again after you've fixed the issue.

Step-by-step debugging

1. Expand the error bubble with ▼.
2. In CEL Expression, copy the failing expression.
3. In Metadata, note the section and index to find the right field in the agent editor.
4. In CEL Variables (requires Debug log level), search for the variable the expression uses and check its actual value.
5. Open the agent editor, go to the relevant tab, and click Expand on the problematic field.
6. Paste the expression into the Test tab, enter realistic variable values, and run it to reproduce the error.
7. Fix the expression and save. The error bubble will stop appearing once the expression succeeds.