OpenAI GPT Converter

Convert Agent Skills into Custom GPTs with awareness of platform constraints and optimal adaptation strategies.

Platform Constraints Summary

Aspect	Claude Skills	Custom GPTs
Instructions	Unlimited (SKILL.md)	8,000 characters
Knowledge Files	Unlimited	20 files max
File Size	Varies by context	512 MB per file
File Structure	Hierarchical	Flat
Executable Scripts	Yes (Python, Bash)	No (Code Interpreter only)
API Integration	Via scripts	Yes (Actions)

For detailed constraints and workarounds, see references/gpt-constraints.md.

Conversion Workflow

Step 1: Audit the Source Skill

Inventory all files in the source skill directory:

Read SKILL.md — note frontmatter fields, body length, and character count
List all files in scripts/, references/, and assets/
Count total files (GPTs allow max 20 knowledge files)
Identify scripts that could use Code Interpreter vs. needing conversion
Identify any API calls that could become GPT Actions

Step 2: Condense SKILL.md for 8,000-Character Limit

This is the critical step. GPT instructions are limited to ~8,000 characters (~130 lines of markdown).

Condensation strategies (in order of preference):

Extract to knowledge files — Move detailed procedures, examples, and reference material into knowledge files. Keep only the core workflow and pointers in instructions.
Remove Claude-specific syntax — Strip file path references, tool invocation syntax, progressive disclosure directives.
Compress verbose sections — Replace multi-paragraph explanations with bullet points.
Use reference pointers — Replace inline content with See [filename] for details.
Prioritize by importance — Cut nice-to-have sections first.

Character budget guidance:

Section	Suggested Budget
Role/purpose statement	~500 chars
Core workflow steps	~3,000 chars
Key rules and constraints	~2,000 chars
Knowledge file pointers	~1,500 chars
Edge cases and warnings	~1,000 chars

Tiered importance for condensation:

Must keep: Core workflow, critical rules, safety constraints
Move to knowledge files: Detailed examples, reference tables, alternative approaches
Can drop: Explanatory context Claude already knows, redundant examples

Step 3: Convert Bundled Resources

Use this naming convention for the flat file structure:

Original:                           Derived:
references/api-docs.md         →    REF_api-docs.md
references/workflows/create.md →    REF_workflows_create.md
scripts/rotate_pdf.py          →    SCRIPT_rotate_pdf.md (converted)
assets/template.pptx           →    ASSET_template.pptx

Prefix system:

REF_ — Reference documentation
SCRIPT_ — Script logic (converted to readable format)
ASSET_ — Binary assets
WORKFLOW_ — Multi-step procedures

Also create REF_extended_instructions.md for any instruction content that was moved out of the 8K character limit.

Step 4: Evaluate Code Interpreter Opportunities

GPTs have Code Interpreter (a Python sandbox). For each script in the source skill:

Script Characteristic	Recommendation
Pure Python, no external deps	Good candidate for Code Interpreter
Requires pip packages	Check if available in Code Interpreter sandbox
Requires network access	Cannot use Code Interpreter — convert to instructions
Requires local file system	Cannot use Code Interpreter — convert to instructions
Simple data processing	Good candidate for Code Interpreter

For Code Interpreter-compatible scripts, include them as knowledge files and instruct the GPT to execute them via Code Interpreter.

Step 5: Evaluate Actions for API Integrations

If the source skill makes API calls via scripts, consider converting to GPT Actions:

Identify API endpoints used in the scripts
Write OpenAPI spec for each endpoint
Configure authentication in the GPT Actions settings
Update instructions to reference the Action instead of the script

Actions are appropriate when:

The skill calls well-defined REST APIs
Authentication can be configured (API key, OAuth)
The API is publicly accessible

Step 6: Consolidate to 20-File Limit

GPTs allow up to 20 knowledge files. If the source skill has more:

Merge related references into single files
Prioritize core documentation
Inline short references into instructions (within 8K limit)
Aim for 10-15 files to leave room for additions

RAG considerations: GPTs use retrieval (RAG) to find relevant knowledge file content. Structure files for chunk-friendly retrieval:

Use clear section headers
Front-load key information in each section
Keep related content together (don't split a topic across files)
Use descriptive file names that indicate content

Step 7: Test the Custom GPT

Create the GPT in the GPT Builder with condensed instructions
Upload all knowledge files
Configure Code Interpreter and/or Actions if applicable
Test with representative queries from the original skill's use cases
Test in long conversations (GPTs can experience prompt drift)
Verify knowledge file retrieval works correctly
Iterate on instructions if the GPT misses important context

Condensation Example

Before (2,500 characters, excerpt):

## PDF Processing

### Overview
This skill provides comprehensive PDF processing capabilities including
text extraction, form filling, document merging, and page manipulation.
It uses pdfplumber for text extraction and pypdf for structural operations.

### Text Extraction
Use pdfplumber for text extraction. Install with pip install pdfplumber.
Then use the following code:
[20 lines of code]

### Form Filling
For form filling, first analyze the form with scripts/analyze_form.py...

After (800 characters):

## PDF Processing

Extract text: `pdfplumber`. Fill forms: analyze → map → validate → fill.
Merge/split: `pypdf`.

See REF_pdf_procedures.md for code examples and detailed steps.
See SCRIPT_form_filling.md for form analysis workflow.

Naming Convention Quick Reference

SKILL.md fields → GPT Configuration:
  name          → GPT Name
  description   → GPT Description
  body          → Instructions (max 8,000 chars)

Resource files → Knowledge Files:
  references/*  → REF_*.md
  scripts/*     → SCRIPT_*.md (or keep .py for Code Interpreter)
  assets/*      → ASSET_*

Quality Expectations

Skill Type	Expected GPT Retention
Documentation/Knowledge	~95%
Workflow guidance	~85%
Code generation guidance	~80%
Automated tasks	~50% (with Code Interpreter)
External API integration	~70% (with Actions)

GPTs retain more capability than Gems due to Code Interpreter and Actions. The main challenge is the 8,000-character instruction limit.

openai-gpt-converter