# 421 Instructions 98648468

> ATaC MCP Server Instructions

- Skill: `tools-only/421-instructions-98648468` (Agent Skill, multi-file: 3 files)
- Install (CLI): `npx skillmds@latest add tools-only/421-instructions-98648468`
- Raw SKILL.md: https://api.skillmd.com/api/skills/tools-only/421-instructions-98648468/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: AI & ML
- Author: tools-only (https://skillmd.com/u/tools-only)
- Updated: 2026-09-22
- Page: https://skillmd.com/skills/tools-only/421-instructions-98648468

---

# ATaC MCP Server Instructions

ATaC (Agentic Trajectory as Code) MCP Server provides tools to programmatically author, inspect, and execute trajectory workspaces (stored as `.atac/<name>/index.yaml`).
Trajectories codify agent actions, conditions, and loops into reusable DSL assets.

## Workflow for LLMs

When interacting with the ATaC MCP Server, follow this general workflow:

1. **Initialize**: Use `atac_init` to create a new, empty trajectory workspace.
2. **Define State**: Use `atac_add_input` to define required runtime parameters.
3. **Build Logic**: 
   - Add tool calls using `atac_add_action`.
   - Add loops using `atac_add_for`.
   - Add conditional branches using `atac_add_if`.
   - Update state using `atac_add_set`.
4. **Targeting (`at` parameter)**: All step addition tools support an `at` parameter to specify where the step should be inserted.
   - `None` (default): Appends to the root level.
   - `0`: Inserts inside the body of step index `0` (e.g., inside a loop).
   - `0.then` or `0.else`: Inserts into conditional branches of an `if` step.
5. **Inspect**: Use `atac_show` to see the current structure and indices to calculate your next `at` path.
6. **Execute**: Use `atac_run` to execute the trajectory with specific inputs.

## Available Tools

- **`atac_init(name: str, description: str)`**
  Creates the base workspace. Example: `atac_init("search_task", "Find data")`

- **`atac_add_input(name: str, input_name: str, type: DataType, default: JsonValue)`**
  Adds a required input. Supported types: `string`, `integer`, `boolean`, `float`, `list`, `object`.
  Example: `atac_add_input("search_task", "cities", "list", ["Beijing", "Shanghai"])`

- **`atac_add_action(name: str, id: str, action: str, args: dict, at: str | None, if_condition: str | None)`**
  Adds an action (tool call).
  `action` takes URIs like `mcp://server_name/tool_name` or `bash://run`.
  *Note on Nested Trajectories*: You can use `bash://run` with `{"command": "atac run child_workspace"}` to nest another trajectory.
  Example: `atac_add_action("search_task", "geo", "mcp://amap-maps/maps_geo", {"address": "${city}"})`

- **`atac_add_for(name: str, in_expr: str, item: str, at: str | None)`**
  Adds a loop. Expressions use Jinja2 syntax.
  Example: `atac_add_for("search_task", "${inputs.cities}", "city")`

- **`atac_add_if(name: str, condition: str, at: str | None)`**
  Adds a conditional branch.
  Example: `atac_add_if("search_task", "${city == 'Beijing'}")`

- **`atac_add_set(name: str, variables: dict, at: str | None)`**
  Sets or updates state variables.
  Example: `atac_add_set("search_task", {"location": "${geo.output.content[0].text.return[0].location}"})`

- **`atac_remove_step(name: str, at: str)`**
  Removes a specific step by its index path.
  Example: `atac_remove_step("search_task", "0.2.then.1")`

- **`atac_list()`**
  Lists all workspaces in the current directory along with their descriptions.
  Returns: A JSON array of workspace metadata.

- **`atac_show(name: str)`**
  Returns the trajectory JSON structure. Use this to understand current step nested paths.

- **`atac_run(name: str, inputs: dict, config_paths: list | None)`**
  Executes the trajectory. Returns JSON outputs.

## Expression Syntax

- **Inputs**: `${inputs.var_name}`
- **Variables**: `${var_name}` (resolves to state variables)
- **Action Outputs**: `${action_id.output}`
  - MCP output: `${action_id.output.content[0].text}`
  - Bash output: `${action_id.output.stdout}`

## Example Usage

1. `atac_init("demo_flow", "Demo App")`
2. `atac_add_input("demo_flow", "targets", "list", ["A", "B"])`
3. `atac_add_for("demo_flow", "${inputs.targets}", "item", None)`
4. `atac_add_action("demo_flow", "echo", "bash://run", {"command": "echo ${item}"}, "0", None)`
5. `atac_run("demo_flow", {"targets": ["X", "Y"]})`