DigiNomads
Harness glossary
The words that decide an agent setup: model, harness, agent, tool, skill, MCP, context window, sandbox, approval policy and headless mode.
The agent market has a vocabulary problem: the same word means a product, a loop and a job title. This page fixes the meanings used across the site. It is a working glossary, not a standards document.
The core four
| Term | What it means here |
|---|---|
| Model | The network that produces tokens. It has a context window, a price and a knowledge cut-off. It does not read your files on its own. |
| Harness | The program around the model: tools, permissions, session storage, context assembly and interface. Claude Code, Codex CLI and Aider are harnesses. |
| Agent | The model plus the harness plus the task loop. When someone says “the agent fixed the bug”, they mean the whole loop, not the weights. |
| Tool | A capability the harness exposes to the model: read a file, run a command, search the web, call an MCP server. A tool is a permission boundary as much as a function. |
A useful sentence: the harness gives the model tools, and the agent is what happens when the model uses them on a task.
Context and memory
| Term | What it means here |
|---|---|
| Context window | The maximum amount of text the model can consider at once, including instructions, files, tool output and the conversation. |
| Context assembly | How the harness decides what enters the window: project instructions, file selection, search results, summaries. Two harnesses with the same model can assemble very different contexts. |
| Compaction | Summarising or dropping older context to stay inside the window. It is lossy; a decision that mattered can disappear. |
| Session | One conversation and its tool history. Resuming a session is not the same as restoring the repository state. |
| Subagent | A separate agent loop, often with its own context, that returns a result to the main session. Useful for research and review; not a substitute for a test. |
Control and safety
| Term | What it means here |
|---|---|
| Permission mode | A preset that decides when the harness asks before acting: for example plan, ask, auto-edit or a fully permissive mode. |
| Approval policy | The rule for when the agent must stop and ask. It can be per tool, per path or per command pattern. |
| Sandbox | An operating-system or container boundary that limits what a command can touch. A permission prompt is not a sandbox. |
| Allowlist / denylist | Explicit rules for commands, paths, domains or tools. Prefer a short allowlist over a long denylist. |
| YOLO mode | A mode that skips approvals. It is a development convenience, not a security posture. |
| Prompt injection | Instructions hidden in content the agent reads, such as a web page or a file, that try to redirect the agent. Treat fetched content as data, not orders. |
Extensibility
| Term | What it means here |
|---|---|
| Skill | A folder of instructions, references and optional scripts that an agent loads when a task matches its description. The open format is documented at agentskills.io. |
| MCP | Model Context Protocol, an open protocol for connecting an agent to tools and data sources through a server. See modelcontextprotocol.io. |
| Plugin | A vendor-specific package that may bundle skills, commands, MCP servers and configuration. Portability depends on the vendor. |
| Headless mode | Running the harness without an interactive interface, usually for scripts and CI. The exact flag and output format differ by harness. |
Workflow words
| Term | What it means here |
|---|---|
| Bake-off | Running the same small set of tasks through two or three harnesses on the same repository, then comparing with a scorecard. The 45-minute version is on this site. |
| Diff | The change between two repository states. A reviewable diff is small, has a reason and does not hide a deleted test. |
| Reproduction | The smallest command that shows the failure. A fix without a reproduction is a hypothesis. |
| Rollback | The documented way to return to the previous state. If it is not written down, it is not a rollback. |
| Portable setup | The instructions, prompts, skills and checks you own in plain files, independent of any one harness. See a portable agent setup. |
What the glossary will not settle
It will not tell you which harness to use, whether a local model is good enough for your work, or whether a permission prompt is safe. Those are decisions about your repository, your client and your risk tolerance. The definitions only make the comparison possible.
Related
- Harness comparison — the table this vocabulary is used to read.
- How to test a harness in 45 minutes — the bake-off protocol.
- A portable agent setup — the files that survive a switch.
Corrections and questions.
Found something wrong, out of date, or worth adding? Send it to the help desk or email corrections@diginomads.win. Confirmed corrections change the page and its reviewed date; the page is also available as Markdown at
/harnesses/glossary.md.
Found a gap in the library?
Send the scenario, the prompt that failed, or the harness change that broke your setup. The help desk takes questions and corrections from humans and agents, and every accepted fix updates the page date.