Contributor Quick Reference

For occasional contributors and PR authors. Full developer docs: https://hermes-agent.nousresearch.com/docs/developer-guide/

Project Layout

hermes-agent/
├── run_agent.py          # AIAgent — core conversation loop
├── model_tools.py        # Tool discovery and dispatch
├── toolsets.py           # Toolset definitions
├── cli.py                # Interactive CLI (HermesCLI)
├── hermes_state.py       # SQLite session store
├── agent/                # Prompt builder, context compression, memory, model routing, credential pooling, skill dispatch
├── hermes_cli/           # CLI subcommands, config, setup, commands
│   ├── commands.py       # Slash command registry (CommandDef)
│   ├── config.py         # DEFAULT_CONFIG, env var definitions
│   └── main.py           # CLI entry point and argparse
├── tools/                # One file per tool
│   └── registry.py       # Central tool registry
├── gateway/              # Messaging gateway
│   └── platforms/        # Platform adapters (telegram, discord, etc.)
├── cron/                 # Job scheduler
├── tests/                # Extensive pytest suite (run via scripts/run_tests.sh)
└── website/              # Docusaurus docs site

Config: ~/.hermes/config.yaml (settings), ~/.hermes/.env (API keys) — both under $HERMES_HOME when it is set.

Adding a Tool

Two files. Auto-discovery imports any tools/*.py with a top-level registry.register() call, but a tool is only exposed to an agent once its name appears in a toolset.

1. Create tools/your_tool.py:

import json, os
from tools.registry import registry

def check_requirements() -> bool:
    return bool(os.getenv("EXAMPLE_API_KEY"))

def example_tool(param: str, task_id: str = None) -> str:
    return json.dumps({"success": True, "data": "..."})

registry.register(
    name="example_tool",
    toolset="example",
    schema={"name": "example_tool", "description": "...", "parameters": {...}},
    handler=lambda args, **kw: example_tool(
        param=args.get("param", ""), task_id=kw.get("task_id")),
    check_fn=check_requirements,
    requires_env=["EXAMPLE_API_KEY"],
)

2. Wire it into a toolset in toolsets.py — add the name to _HERMES_CORE_TOOLS (every platform) or to a specific toolset.

All handlers must return JSON strings. Use get_hermes_home() for paths, never hardcode ~/.hermes. For custom/local-only tools, write a plugin in ~/.hermes/plugins/ instead of editing core — see the developer docs.

Adding a Slash Command

Add CommandDef to COMMAND_REGISTRY in hermes_cli/commands.py
Add handler in cli.py → process_command()
(Optional) Add gateway handler in gateway/run.py

All consumers (help text, autocomplete, Telegram menu, Slack mapping) derive from the central registry automatically.

Agent Loop (High Level)

run_conversation():
  1. Build system prompt
  2. Loop while iterations < max:
     a. Call LLM (OpenAI-format messages + tool schemas)
     b. If tool_calls → dispatch each via handle_function_call() → append results → continue
     c. If text response → return
  3. Context compression triggers automatically near token limit

Testing

Use the canonical runner — it enforces CI-parity (hermetic env -i, unset credentials, TZ=UTC, per-file subprocess isolation via scripts/run_tests_parallel.py — no xdist, worker count auto-scaled):

scripts/run_tests.sh                          # full suite
scripts/run_tests.sh tests/tools/             # one directory
scripts/run_tests.sh tests/tools/test_x.py    # one file
scripts/run_tests.sh -v --tb=long             # pass-through pytest flags

Tests auto-redirect HERMES_HOME to temp dirs — never touch real ~/.hermes/.
The script probes .venv, then venv, then the shared worktree venv.
Windows: the wrapper is POSIX-only; see references/windows-quirks.md for the direct-pytest workaround.

Cross-platform test guards: tests using POSIX-only syscalls need a skip marker. Common ones already in the codebase:

Symlink creation → @pytest.mark.skipif(sys.platform == "win32", reason="Symlinks require elevated privileges on Windows") (see tests/cron/test_cron_script.py)
POSIX file modes (0o600, etc.) → @pytest.mark.skipif(sys.platform.startswith("win"), reason="POSIX mode bits not enforced on Windows") (see tests/hermes_cli/test_auth_toctou_file_modes.py)
signal.SIGALRM → Unix-only (per-test timeouts no longer use it directly; see the win32 timeout-method shim in tests/conftest.py::pytest_configure)
Live Winsock / Windows-specific regression tests → @pytest.mark.skipif(sys.platform != "win32", reason="Windows-specific regression")

Monkeypatching sys.platform is not enough when the code under test also calls platform.system() / platform.release() / platform.mac_ver(). Those functions re-read the real OS independently, so a test that sets sys.platform = "linux" on a Windows runner will still see platform.system() == "Windows" and route through the Windows branch. Patch all three together:

monkeypatch.setattr(sys, "platform", "linux")
monkeypatch.setattr(platform, "system", lambda: "Linux")
monkeypatch.setattr(platform, "release", lambda: "6.8.0-generic")

See tests/agent/test_prompt_builder.py::TestEnvironmentHints for a worked example.

System prompt's execution-environment block

Factual host/backend guidance (OS, $HOME, cwd, terminal backend, shell) is emitted by agent/prompt_builder.py::build_environment_hints(). The key invariant for prompt authors: with a remote terminal backend (docker, singularity, modal, daytona, ssh, managed_modal), host info is suppressed and every file tool runs inside the backend container — the prompt must never describe the host the agent can't touch.

Commit Conventions

type: concise subject line

Optional body.

Types: fix:, feat:, refactor:, docs:, chore:

Key Rules

Never break prompt caching — don't change context, tools, or system prompt mid-conversation
Message role alternation — never two assistant or two user messages in a row
Use get_hermes_home() from hermes_constants for all paths (profile-safe)
Config values go in config.yaml, secrets go in .env
New tools need a check_fn so they only appear when requirements are met

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