AI Tool Schema Builder
Build JSON tool and function-call schemas for OpenAI, Anthropic and MCP from one visual form. Add parameters with types, enums and required flags, get validation as you type, and copy the finished definition. No API key, nothing uploaded.
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What is AI Tool Schema Builder?
AI Tool Schema Builder turns one plain description of a tool into the exact JSON definition each vendor expects. You fill in the tool name, a description and the parameters once — each with its type, description, enum values and required flag — and the builder emits the JSON Schema body plus the wrapper for the format you select: a function entry for OpenAI, a tools entry with input_schema for Anthropic, or an inputSchema entry for MCP. Every field is validated offline against the rules of the selected provider, so a call is not rejected after you have already wired it into the application.
Key Benefits
- Describe a tool once and emit OpenAI, Anthropic and MCP definitions from the same form
- Offline validation of tool names, parameter names, duplicates, enum values and strict-mode requirements
- Numeric enums are emitted as JSON numbers rather than strings, which is the detail that quietly breaks tool calling
- Warnings for the things that only degrade tool selection, such as missing descriptions
- No account, no API key and no upload, so schemas for private internal tools stay on your machine
Common Use Cases
- •Adding a first function-calling tool to an OpenAI or Anthropic request without hand-writing JSON
- •Sharing one tool definition across an OpenAI app and an MCP server
- •Checking why a tool call is being rejected by comparing the definition against the naming and strict-mode rules
- •Documenting an internal API as a tool schema that several teams can reuse
How to Use AI Tool Schema Builder
- Name and describe the tool: Type the tool name a model will call and a one-sentence description of what it does. The name hint tells you which characters OpenAI, Anthropic and MCP each accept.
- Add the parameters: Add one row per parameter, then set its type, description, enum values and required flag. Array parameters also take an element type, and the emitted JSON Schema updates as you type.
- Clear the reported issues: Errors block the copy button and explain exactly what a vendor API would reject, such as a dotted name on the OpenAI tab or an optional parameter while strict mode is on. Warnings flag things that only degrade tool selection.
- Pick the format and copy it: Switch between the OpenAI, Anthropic and MCP tabs. The schema body stays the same and only the wrapper changes, so copy the tab you need or download it as a JSON file.
Key Features
- Visual parameter editor with types, descriptions, enums, array element types and required flags
- One-click output for OpenAI function entries, Anthropic tools entries and MCP inputSchema entries
- Offline validation of tool names, parameter names, duplicate parameters, enum values and strict-mode rules
- Numeric enums are emitted as JSON numbers, not strings — the detail that silently breaks tool calling
- Warnings for missing descriptions and enums that the selected parameter type cannot carry
- Copy or download the finished definition, or load a ready-made example to start from