Function Calling Overhead Calculator
See the token cost of sending tool schemas on every call.
With the default inputs, $1,080.00/month in tool-schema overhead — 1,440 tokens of schemas sent every call. Enter your own numbers below to recompute instantly; the full step-by-step math is shown under the worked example.
Results update automatically as you type.
- Tools
- 12
- Schema tokens (total)
- 1,440 tokens
- Overhead / call
- $0.00180
- Overhead / month
- $1,080.00
Tool/function schemas are sent as input tokens on every request. Estimate how much that overhead costs across your call volume.
How this is calculated
Overhead cost = number of tools × tokens per tool schema × input price × calls per day × 30. Because tool/function schemas are sent as input tokens on every request, a large tool set quietly adds fixed input to every single call.
Is this a good result? What to do next
This is a fixed tax you pay on every request whether or not a tool is used. With many tools or verbose schemas it can rival the cost of the actual prompt — dynamic tool selection is the biggest lever.
Typical planning ranges
- Overhead billed
- on every request
- Cost drivers
- tool count × schema size
- Big lever
- dynamic tool selection
Ranges are typical planning figures to sanity-check your result, not authoritative benchmarks. Your numbers will vary with use case, volume, and vendor.
How to improve this number
- Send only the tools relevant to each request.
- Trim schema descriptions and parameter docs.
- Cache the tool block where the provider supports it.
Common mistakes
- Sending all tools on every call by default.
- Verbose schemas that inflate fixed overhead.
When to use a different approach
For the cost of executing calls, use the tool call cost calculator. For MCP tool interactions, use the MCP server cost calculator.
Worked example (defaults)
With the default inputs above, here is the result:
- Tools
- 12
- Schema tokens (total)
- 1,440 tokens
- Overhead / call
- $0.00180
- Overhead / month
- $1,080.00
- Every request re-sends all tool JSON schemas as input tokens.
Sources & references
Frequently asked questions
How do I reduce tool overhead?+
Send only the tools relevant to each request, trim schema descriptions, and cache the tool block if the provider supports it.
Does every call include all tools?+
By default yes — which is why large tool sets add up. Dynamic tool selection helps a lot.