API Designer
Jeffallan/claude-skills
Designs REST and GraphQL APIs from resource modeling to an OpenAPI 3.1 contract, with versioning, pagination and RFC 7807 error handling.
Call any REST API dynamically. An agent skill from NVIDIA/SkillEvaluator.
Install API Caller
$ npx skills add NVIDIA/SkillEvaluator --skill api-caller -a claude-codeProject install by default; add -g for ~/.claude/skills/.
$ gh skill install NVIDIA/SkillEvaluator api-caller --agent claude-codeProject scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).
$ git clone --depth 1 https://github.com/NVIDIA/SkillEvaluator.git skills-src && mkdir -p .claude/skills && cp -r skills-src/src/skillevaluator/tier3/reference_skills/api-caller .claude/skills/api-caller && rm -rf skills-srcUse ~/.claude/skills/ instead of .claude/skills for a personal install. The folder must contain SKILL.md.
Claude Code skills documentation · loads skills from .claude/skills/
Install the "api-caller" agent skill from https://github.com/NVIDIA/SkillEvaluator/tree/main/src/skillevaluator/tier3/reference_skills/api-caller into .claude/skills/api-caller/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "api-caller", then confirm the skill loads.Claude Code copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$skill-installer install https://github.com/NVIDIA/SkillEvaluator/tree/main/src/skillevaluator/tier3/reference_skills/api-callerType this inside Codex. $skill-installer <name> installs a curated skill from openai/skills. The installer writes to $CODEX_HOME/skills (default ~/.codex/skills). Restart Codex if the skill does not show up.
$ npx skills add NVIDIA/SkillEvaluator --skill api-caller -a codexProject install goes to .agents/skills/; add -g for ~/.codex/skills/.
$ gh skill install NVIDIA/SkillEvaluator api-caller --agent codexProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/NVIDIA/SkillEvaluator.git skills-src && mkdir -p .agents/skills && cp -r skills-src/src/skillevaluator/tier3/reference_skills/api-caller .agents/skills/api-caller && rm -rf skills-srcUse ~/.agents/skills/ instead of .agents/skills for a personal install.
Codex skills documentation · loads skills from .agents/skills/
Install the "api-caller" agent skill from https://github.com/NVIDIA/SkillEvaluator/tree/main/src/skillevaluator/tier3/reference_skills/api-caller into .agents/skills/api-caller/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "api-caller", then confirm the skill loads.Codex copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ npx skills add NVIDIA/SkillEvaluator --skill api-caller -a cursorProject install goes to .agents/skills/; add -g for ~/.cursor/skills/.
$ gh skill install NVIDIA/SkillEvaluator api-caller --agent cursorProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/NVIDIA/SkillEvaluator.git skills-src && mkdir -p .cursor/skills && cp -r skills-src/src/skillevaluator/tier3/reference_skills/api-caller .cursor/skills/api-caller && rm -rf skills-srcUse ~/.cursor/skills/ instead of .cursor/skills for a personal install.
Cursor skills documentation · loads skills from .cursor/skills/, .agents/skills/, .claude/skills/, .codex/skills/
Install the "api-caller" agent skill from https://github.com/NVIDIA/SkillEvaluator/tree/main/src/skillevaluator/tier3/reference_skills/api-caller into .cursor/skills/api-caller/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "api-caller", then confirm the skill loads.Cursor copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ gemini skills install https://github.com/NVIDIA/SkillEvaluator.git --path src/skillevaluator/tier3/reference_skills/api-caller--scope user (default) or --scope workspace; --path is the subfolder of the repo that holds the skill; --consent skips the security confirmation prompt.
$ npx skills add NVIDIA/SkillEvaluator --skill api-caller -a gemini-cliProject install goes to .agents/skills/; add -g for ~/.gemini/skills/.
$ gh skill install NVIDIA/SkillEvaluator api-caller --agent gemini-cliProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/NVIDIA/SkillEvaluator.git skills-src && mkdir -p .gemini/skills && cp -r skills-src/src/skillevaluator/tier3/reference_skills/api-caller .gemini/skills/api-caller && rm -rf skills-srcUse ~/.gemini/skills/ instead of .gemini/skills for a personal install, then run /skills reload.
Gemini CLI skills documentation · loads skills from .gemini/skills/, .agents/skills/
Install the "api-caller" agent skill from https://github.com/NVIDIA/SkillEvaluator/tree/main/src/skillevaluator/tier3/reference_skills/api-caller into .gemini/skills/api-caller/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "api-caller", then confirm the skill loads.Gemini CLI copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ gh skill install NVIDIA/SkillEvaluator api-callerInstalls for Copilot at project scope by default; add --scope user for a personal install. Preview a skill first with gh skill preview. Needs GitHub CLI 2.90.0 or later (public preview).
$ npx skills add NVIDIA/SkillEvaluator --skill api-caller -a github-copilotProject install goes to .agents/skills/; add -g for ~/.copilot/skills/.
$ git clone --depth 1 https://github.com/NVIDIA/SkillEvaluator.git skills-src && mkdir -p .github/skills && cp -r skills-src/src/skillevaluator/tier3/reference_skills/api-caller .github/skills/api-caller && rm -rf skills-srcUse ~/.copilot/skills/ instead of .github/skills for a personal install. Commit .github/skills so cloud agent and code review can use it.
GitHub Copilot skills documentation · loads skills from .github/skills/, .claude/skills/, .agents/skills/
Install the "api-caller" agent skill from https://github.com/NVIDIA/SkillEvaluator/tree/main/src/skillevaluator/tier3/reference_skills/api-caller into .github/skills/api-caller/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "api-caller", then confirm the skill loads.GitHub Copilot copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ npx skills add NVIDIA/SkillEvaluator --skill api-caller -a opencodeOpenCode documents no install command of its own. Project install goes to .agents/skills/; add -g for ~/.config/opencode/skills/.
$ gh skill install NVIDIA/SkillEvaluator api-caller --agent opencodeProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/NVIDIA/SkillEvaluator.git skills-src && mkdir -p .opencode/skills && cp -r skills-src/src/skillevaluator/tier3/reference_skills/api-caller .opencode/skills/api-caller && rm -rf skills-srcUse ~/.config/opencode/skills/ instead of .opencode/skills for a personal install.
OpenCode skills documentation · loads skills from .opencode/skills/, .claude/skills/, .agents/skills/
Install the "api-caller" agent skill from https://github.com/NVIDIA/SkillEvaluator/tree/main/src/skillevaluator/tier3/reference_skills/api-caller into .opencode/skills/api-caller/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "api-caller", then confirm the skill loads.OpenCode copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
Facts
- Skill name
api-caller- GitHub stars
- 544
- Used in
- 1 other repo
- Token cost
- ~1.1k tokens
- SKILL.md length
- 411 words
- Files
- 5 (incl. scripts, references)
- Skills in repo
- 5
- Repo updated
- First seen
- Licence
- Apache-2.0
At a glance
Call any REST API dynamically. An agent skill from NVIDIA/SkillEvaluator.
- Works in 4 steps: Read this SKILL.md to choose the… → Use scripts/parse_openapi.py first when… → Use scripts/call_api.py for the actual… → …
- Tasks that involve OpenAPI specifications
- SKILL.md covers Capabilities, Instructions, Scripts and Examples, plus 4 more sections
- Runs Python scripts from its folder; calls python; reaches en.wikipedia.org
What it does
API Caller is an agent skill from NVIDIA/SkillEvaluator, published by the product's own GitHub organization. Call any REST API dynamically. Make GET, POST, PUT, DELETE requests to any endpoint with custom headers and JSON body.
Its SKILL.md is about 1.1k tokens, which your agent loads only when the skill is triggered. The skill folder holds 7 other files, including scripts and reference files (for example `evals/evals.json`, `references/common_apis.md` and `scripts/call_api.py`).
It sits in Backend & APIs, covering OpenAPI specifications, REST APIs and Agent evaluation and testing. It works with OpenAPI. The repository describes itself as: Multi-tier framework for evaluating AI agent skills with quality gates, semantic overlap detection, synthetic evaluation dataset generation, and live agent evaluation that… The licence is Apache-2.0.
When your agent uses it
- Tasks that involve OpenAPI specifications
- Tasks that involve REST APIs
- Tasks that involve Agent evaluation and testing
Example prompts
- “/api-caller”
Requirements
- Python 3
Workflow steps
4 steps, taken from the first numbered list in SKILL.md.
- Read this SKILL.md to choose the direct-call or OpenAPI workflow.
- Use scripts/parse_openapi.py first when the user gives an OpenAPI or Swagger spec.
- Use scripts/call_api.py for the actual HTTP request.
- Return the request result and any recoverable error details to the user.
What it can do on your machine
Read from SKILL.md and the folder at commit f32c884. It shows what the files ask for, not the result of running them.
Tool permissions
Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.
From allowed-tools in the SKILL.md frontmatter.
Runs code
Ships 2 files in scripts/ (Python), which the agent can run.
Shell commands in SKILL.md call:
python
From the folder's file list and the shell code blocks in SKILL.md.
Network
Hosts in commands or code, which the agent is likely to contact:
en.wikipedia.org
From URLs in SKILL.md, links to its own repository left out.
Credentials
Names no API keys, tokens, secrets or passwords.
From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.
Context cost
API Caller loads about 1.1k tokens when it runs, and up to ~1.5k if it reads all its reference files. Until then it costs about 32 tokens; SKILL.md has 411 words of instructions outside code blocks.
Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.
Safety
Auto-check passed
The automated check found no risky patterns in SKILL.md.
Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); the scripts in this folder are not scanned.
SKILL.md
The full file from NVIDIA/SkillEvaluator at commit f32c884, republished under its Apache-2.0 licence (© NVIDIA). 411 words, ~1,094 tokens.
Download SKILL.mdSave it as
.claude/skills/api-caller/SKILL.md (or your agent's skills folder). This skill also uses 4 other files; get the full folder from GitHub.- name
- api-caller
- description
- Call any REST API dynamically. Make GET, POST, PUT, DELETE requests to any endpoint with custom headers and JSON body.
- metadata.author
- SkillEvaluator Maintainers <maintainers@example.com>
API Caller Skill
Generic skill to call any REST API dynamically. Can work with OpenAPI specs or direct endpoint calls.
Capabilities
- Call any REST API endpoint (GET, POST, PUT, DELETE)
- Parse OpenAPI/Swagger specs to discover endpoints
- Handle common authentication (API keys, Bearer tokens)
- JSON request/response handling
Instructions
- Read this SKILL.md to choose the direct-call or OpenAPI workflow.
- Use
scripts/parse_openapi.pyfirst when the user gives an OpenAPI or Swagger spec. - Use
scripts/call_api.pyfor the actual HTTP request. - Return the request result and any recoverable error details to the user.
Scripts
scripts/parse_openapi.py
Use this first when given an API spec URL. Parses an OpenAPI/Swagger spec and returns available operations with parameters. Run commands from the skill base directory; script paths are relative to this SKILL.md file.
Usage:
python scripts/parse_openapi.py <spec_url> [filter_path]Arguments:
<spec_url>- URL to the OpenAPI spec (required)[filter_path]- Optional: filter operations by path substring
Example:
python scripts/parse_openapi.py "https://api.example.com/openapi.json"Returns: API name, base URL, and list of operations with their parameters, request body schema, etc.
scripts/call_api.py
Call a REST API endpoint directly or using an OpenAPI spec. Run commands from the skill base directory; script paths are relative to this SKILL.md file.
Usage:
python scripts/call_api.py --url <endpoint_url> [options]Arguments:
--url <endpoint_url>- Direct API endpoint URL (required if no --spec)--method <GET|POST|PUT|DELETE>- HTTP method (default: GET)--data <json_string>- Request body as JSON string--headers <json_string>- Custom headers as JSON string--spec <openapi_url>- OpenAPI spec URL (optional, for discovery)--operation <operation_id>- Operation ID from OpenAPI spec--params <json_string>- Path/query parameters as JSON
Examples
Direct API Call (Simple)
python scripts/call_api.py --url "https://api.example.com/data" --method GETWith Query Parameters
# Call API with query parameters appended to URL
python scripts/call_api.py --url "https://en.wikipedia.org/w/api.php" --params '{"action": "query", "titles": "NVIDIA", "format": "json"}'Show full SKILL.md (166 more words)Show less
With Headers (API Key)
# Call API with authentication
python scripts/call_api.py --url "https://api.example.com/data" --headers '{"Authorization": "Bearer TOKEN"}'POST with JSON Body
# Create a resource
python scripts/call_api.py --url "https://api.example.com/items" --method POST --data '{"name": "test", "value": 123}'Using OpenAPI Spec (Advanced)
# Discover and call an endpoint from OpenAPI spec
python scripts/call_api.py --spec "https://api.example.com/openapi.json" --operation "getItems" --params '{"param": "value"}'Notes
- For APIs requiring authentication, pass API keys via
--headers - The skill automatically parses JSON responses
- Timeout is 30 seconds by default
- For complex API workflows, consider using
code-generatorskill instead - Limiting results: Try common params like
?_limit=N,?limit=N,?per_page=N. If unsupported, fetch all and filter withcode-generator
Workflow: Using an API Spec
When given an OpenAPI spec URL, follow this workflow:
Parse the spec first with
python scripts/parse_openapi.py:bash python scripts/parse_openapi.py "<spec_url>"Review operations - Look at the returned operations, their paths, methods, and parameters
Call the API with
python scripts/call_api.pyusing the discovered endpoint and parameters
When to Use
- Quick API calls without writing code
- Exploring new APIs
- Simple GET requests for data retrieval
- When you know the exact endpoint URL
- When given an API spec to explore
When NOT to Use
- Complex multi-step API workflows (use
code-generator) - APIs requiring OAuth flows
- When you need to process response data extensively
© NVIDIA, Apache-2.0. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file
Files
SKILL.md and 4 other files (scripts, references) in src/skillevaluator/tier3/reference_skills/api-caller of NVIDIA/SkillEvaluator.
- SKILL.md
- evals/evals.json
- references/common_apis.md
- scripts/call_api.py
- scripts/parse_openapi.py
Open the folder on GitHubat commit f32c884
Used in 1 other repository
We found 1 copy of this SKILL.md (exact, near-identical or edited) in other folders, from 1 other GitHub owner. This page covers the copy in NVIDIA/SkillEvaluator, which our catalogue first saw on October 7, 2026.
Compare with similar skills
API Caller next to the 5 skills that share the most tags, products or categories with it. Stars are the repository's; “used in” counts other GitHub owners with a copy.
| Skill | Stars | Used in | Tokens | Auto-check | Licence | Repo updated |
|---|---|---|---|---|---|---|
| API Caller this skillNVIDIA/SkillEvaluator | 544 | 1 repos | ~1.1k | Automated safety check: Pass | Apache-2.0 | |
| API DesignerJeffallan/claude-skills | 12k | 2 repos | ~2k | Automated safety check: Pass | MIT | |
| OpenAPI to MCP Servermcp-use/mcp-use | 11k | — | ~5.2k | Automated safety check: Pass | Apache-2.0 | |
| Use Yaakmountain-loop/yaak | 19k | — | ~1.9k | Automated safety check: Pass | MIT | |
| Old Coder API DesignAmazingAng/old-coder | 749 | 1 repos | ~3.4k | Automated safety check: Pass | MIT | |
| API Generatinghuangjia2019/claude-code-engineering | 1.1k | 1 repos | ~379 | Automated safety check: Pass | None |
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Related
Works with
Categories
Questions about API Caller
What does API Caller do?
Call any REST API dynamically. An agent skill from NVIDIA/SkillEvaluator. API Caller is an agent skill from NVIDIA/SkillEvaluator, published by the product's own GitHub organization. Call any REST API dynamically.
When should I use API Caller?
API Caller fits situations like: tasks that involve OpenAPI specifications; tasks that involve REST APIs; tasks that involve Agent evaluation and testing.
How do I install API Caller in Claude Code?
Run `npx skills add NVIDIA/SkillEvaluator --skill api-caller -a claude-code`. Or copy the skill folder (src/skillevaluator/tier3/reference_skills/api-caller in NVIDIA/SkillEvaluator) into .claude/skills/api-caller in your project. Claude Code loads it when a task matches its description.
How do I install API Caller in Codex?
Run `npx skills add NVIDIA/SkillEvaluator --skill api-caller -a codex`. Or copy the skill folder (src/skillevaluator/tier3/reference_skills/api-caller in NVIDIA/SkillEvaluator) into .agents/skills/api-caller in your project. Codex loads it when a task matches its description.
Can I use API Caller in Cursor, Gemini CLI or GitHub Copilot?
Cursor, Gemini CLI, GitHub Copilot and OpenCode also load SKILL.md folders. With the skills CLI, run `npx skills add NVIDIA/SkillEvaluator --skill api-caller -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/api-caller, .gemini/skills/api-caller, .github/skills/api-caller and .opencode/skills/api-caller in your project.
What does API Caller need to run?
Going by SKILL.md and its folder, API Caller needs Python for the scripts in its folder and the command-line tools its instructions call (python). Our summary lists: Python 3.
Does API Caller access the network?
SKILL.md names 1 domain. In commands or code: en.wikipedia.org; the agent is likely to contact it when it follows the instructions. This is read from the text; nothing was executed.
Is API Caller safe to install?
Our automated static check of SKILL.md found no risky patterns, such as piping downloads into a shell, reading credential files or hidden Unicode. It is not a guarantee. The check reads SKILL.md only: the scripts in the folder are not scanned, so read them before running anything.
What licence does API Caller use?
API Caller is published under the Apache-2.0 licence (the repository's licence). It allows redistribution, so the full SKILL.md is shown on this page.
How many tokens does API Caller use?
About 1.1k tokens (SKILL.md is roughly 4.4k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full. Its references folder adds about 396 tokens, read only when the agent opens those files.
What are the alternatives to API Caller?
Skills that share tags, products or a category with API Caller: API Designer (Jeffallan/claude-skills, 12k stars), OpenAPI to MCP Server (mcp-use/mcp-use, 11k stars), Use Yaak (mountain-loop/yaak, 19k stars) and Old Coder API Design (AmazingAng/old-coder, 749 stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.
Who maintains API Caller?
NVIDIA (a GitHub organization, an official publisher) maintains it in NVIDIA/SkillEvaluator, which has 544 GitHub stars. The repository holds 5 skills in this directory. The repository was last updated on October 7, 2026.
Source: NVIDIA/SkillEvaluator on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.