Tool Use / Function Calling Engineer.
St. Louis.
$167,000
median salary, 10% below the national average
$124,000 to $218,000. Updated for 2026.
The numbers.
Everything you need to negotiate with confidence.
St. Louis is 10% cheaper than the national average. For Tool Use / Function Calling Engineers, that shakes out to a median of $167,000, with the full range spanning $124,000 to $218,000. Compensation scales with the complexity and reliability of tool integration systems built. Know the range before you walk in.
Salary range
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How St. Louis compares
St. Louis, MO
$167,000
Cost of living: 10% below average
National Average
$185,000
St. Louis is $18,000 below
What you should know
Here is what the Tool Use / Function Calling Engineer market actually looks like in St. Louis. St. Louis offers one of the most affordable major metro areas in the country, with a strong base in healthcare, financial services, and manufacturing. The region's anchor employers include Boeing, Centene, and Washington University's medical campus. A growing biotech and plant sciences corridor centered on the Cortex Innovation District is attracting new investment and talent. Compensation scales with the complexity and reliability of tool integration systems built. Engineers who can design robust function calling frameworks with error recovery and multi-step planning earn premiums. Experience with multiple LLM providers and enterprise API ecosystems drives salaries 10% to 18% above median.
Junior tool integration engineers start near $138,000 building basic function schemas. Mid-level engineers designing robust multi-tool orchestration earn $183,000 to $210,000. Principal engineers architecting enterprise tool-use platforms reach $242,000 to $290,000. In St. Louis, cost of living sits near the national average, so the numbers you see are roughly what you keep.
Base salary is not the full picture. Equity at AI platform companies is a significant compensation component. Performance bonuses of 12% to 18% are standard, with some roles offering developer ecosystem growth bonuses tied to platform adoption metrics. And on the tax side: missouri's top income tax rate is about 4.8%, and St. Louis City adds a 1% earnings tax. The low base cost of living means your after tax salary still stretches further than in most metros. When someone quotes you $167,000, ask what the total package looks like. The gap between base and total comp is where real money hides.
On negotiation: Emphasize your willingness to work in person at Cortex or the BJC campus. St. Louis employers offer higher packages for candidates who commit to the local innovation hubs. The range for Tool Use / Function Calling Engineers in St. Louis runs from $124,000 to $218,000. That is not a narrow window. Where you land inside it depends almost entirely on whether you negotiate and how well you prepare.
Top industries in St. Louis
Negotiating in St. Louis
Emphasize your willingness to work in person at Cortex or the BJC campus. St. Louis employers offer higher packages for candidates who commit to the local innovation hubs.