add-tool

A development guide for adding a new tool to OhMyCode, so the assistant can perform an additional kind of task during conversations.

In plain words
What is it for?
Use it when creating a custom tool, such as one for running SQL queries, including its inputs, implementation and tests.
Why use it?
It provides the project-specific structure and checks needed to add a tool consistently, instead of guessing how the codebase works.

Skill for Claude CodeCodex

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/alphalab-ustc/ohmycode/add-tool
Any agent
npx skills add AlphaLab-USTC/OhMyCode --skill add-tool
Clone the repo
git clone --depth 1 https://github.com/AlphaLab-USTC/OhMyCode

Made for: Claude Code, Codex.

Per session 24 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 788 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00024 $0.00788
Opus 5 $0.00012 $0.00394
Sonnet 5 $0.00005 $0.00158
Haiku 4.5 $0.00002 $0.00079

Measured 3d ago against content hash e7313d6cdcb8, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

add-tool scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 3d ago.

The scan reads SKILL.md. This mod also ships 1 executable file (templates/tool_template.py), listed below but not scanned — reading those needs a real analyzer, not pattern matching.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

.agents/skills/add-tool/SKILL.md · 96 lines

How it starts

The opening of the file, as written. The whole thing — 96 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Add a New Tool to OhMyCode

Create a new tool that the AI assistant can use during conversations.

When to Use

  • User says "add a tool", "create a tool", "I want a new tool"
  • User describes a capability they want the AI to have (e.g., "I want it to run SQL queries")

Prerequisites

  • Read docs/DEVELOPMENT_GUIDE.md for project conventions
  • Read ohmycode/tools/base.py to understand Tool, ToolContext, ToolResult, @register_tool
  • Look at an existing tool (e.g., ohmycode/tools/bash.py) as reference

Step-by-Step Guide

Step 1: Define the Tool

Ask the user:

  1. Tool name — short, lowercase, snake_case (e.g., sql_query, docker_run)
  2. Description — one sentence for the LLM to understand when to use it
  3. Parameters — what inputs does it need? (JSON Schema format)
  4. Concurrent safety — can it run in parallel with other tools? (True for read-only, False for side effects)

Step 2: Create the Tool File

Copy the template from templates/tool_template.py to ohmycode/tools/<tool_name>.py.

Fill in:

  • name, description, parameters, concurrent_safe class attributes
  • execute() method with the actual logic

Step 3: Write Tests (TDD)

Create tests/tools/test_<tool_name>.py:

import pytest
from ohmycode.tools.base import ToolContext
from ohmycode.tools.<tool_name> import <ToolClass>

@pytest.fixture
def ctx(tmp_path):
    return ToolContext(mode="auto", agent_depth=0, cwd=str(tmp_path), is_sub_agent=False)

@pytest.mark.asyncio
async def test_<tool_name>_basic(ctx):
    tool = <ToolClass>()
    result = await tool.execute({"param": "value"}, ctx)
    assert not result.is_error
    assert "expected" in result.output

Step 4: Verify

python3 -m pytest tests/tools/test_<tool_name>.py -v   # New tests pass
python3 -m pytest tests/ -v                              # No regressions

Step 5: Test End-to-End

ohmycode -p "Use the <tool_name> tool to ..." --mode auto

Step 6: Commit

Read the full file on GitHub · 96 lines

Files

What ships with it

1 file beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 3d ago First seen · 96 lines · 24 tokens per session scan A e7313d6cdcb8

Subscribe to this mod's changes

add-tool is a skill published in the GitHub repository AlphaLab-USTC/OhMyCode (131 stars, last pushed 5mo ago), licensed MIT. It adds 24 tokens to every session and 788 once invoked, about $0.0001 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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