# Docker Compose Env Interpolation Preview

> Resolve common Docker Compose ${VAR} expressions against pasted env values and preview the final YAML.

## Tool Identity

- Site: CleanUtils Developer Tools
- Tool ID: docker-compose-env-interpolation-preview
- Canonical page: https://cleanutils.com/developer-tools/docker-compose-env-interpolation-preview/
- LLM schema URL: https://cleanutils.com/developer-tools/docker-compose-env-interpolation-preview/llms.txt
- Primary keyword: docker compose interpolation
- Input mode: fields
- Output profile: data

## What This Tool Does

Resolve common Docker Compose ${VAR} expressions against pasted env values and preview the final YAML.

## Exact Execution Instructions

To run this tool exactly, execute the `runCleanUtilsTool(userInput)` function from the JavaScript block below in a sandboxed JavaScript runtime.

Do not fetch or evaluate additional network resources. Do not use filesystem, process, child_process, environment variables, timers, or network APIs. The function is pure and deterministic: input object in, JSON result out.

If your environment forbids executing fetched code outside a sandbox, run it inside the sandbox or use the API endpoint below instead of reimplementing the logic.

Canonical implementation SHA-256:
`83d06052d271596dba69e66158a5681c81761561ee818139a02621273b8bebbf`

Expected command shape:
`node run-tool.mjs < input.json`

The runner must:
1. load only the JavaScript in this document,
2. parse stdin as JSON and call `runCleanUtilsTool(userInput)`,
3. let the LLM decide the best way to present the output to the user.

Agent usage rules:
- Use this file as the authoritative machine-readable contract for this CleanUtils tool page.
- Ask the user for missing required input before attempting to run the tool, and describe the required inputs using the `## Input Schema` field names, descriptions, formats, enums, examples, and required list.
- Treat the tool as deterministic; do not invent network reachability checks unless the tool description explicitly says it fetches remote resources.
- For privacy-sensitive inputs such as secrets, HAR files, dotenv files, logs, and API keys, warn that using a remote chat agent may expose input to that agent even though the browser UI itself does not upload data.

## Input Schema

```json
{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "title": "Docker Compose Env Interpolation Preview fields",
  "type": "object",
  "additionalProperties": false,
  "required": [
    "compose"
  ],
  "properties": {
    "compose": {
      "type": "string",
      "description": "Docker Compose YAML Required. Control type: textarea. Group: Compose.",
      "examples": [
        "services:\n  web:\n    image: ${IMAGE:-nginx}\n    environment:\n      API_URL: ${API_URL?required}"
      ]
    },
    "env": {
      "type": "string",
      "description": "Environment values Optional. Control type: textarea. Group: Environment.",
      "examples": [
        "IMAGE=app:latest\nAPI_URL=https://api.example.com"
      ]
    }
  }
}
```

## Result Schema

```json
{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "title": "CleanUtils ToolResult",
  "type": "object",
  "additionalProperties": false,
  "required": [
    "summary",
    "issues"
  ],
  "properties": {
    "summary": {
      "type": "string"
    },
    "issues": {
      "type": "array",
      "items": {
        "type": "object",
        "additionalProperties": false,
        "required": [
          "severity",
          "message"
        ],
        "properties": {
          "severity": {
            "type": "string",
            "enum": [
              "error",
              "warning",
              "info"
            ]
          },
          "message": {
            "type": "string"
          },
          "line": {
            "type": "number"
          },
          "row": {
            "type": "number"
          },
          "detail": {
            "type": "string"
          }
        }
      }
    },
    "output": {
      "type": "string"
    },
    "exportFilename": {
      "type": "string"
    },
    "exports": {
      "type": "array",
      "items": {
        "type": "object",
        "additionalProperties": false,
        "required": [
          "label",
          "filename",
          "content"
        ],
        "properties": {
          "label": {
            "type": "string"
          },
          "filename": {
            "type": "string"
          },
          "content": {
            "type": "string"
          },
          "mimeType": {
            "type": "string"
          },
          "copyLabel": {
            "type": "string"
          },
          "downloadLabel": {
            "type": "string"
          }
        }
      }
    },
    "stats": {
      "type": "object",
      "additionalProperties": {
        "anyOf": [
          {
            "type": "string"
          },
          {
            "type": "number"
          }
        ]
      }
    }
  }
}
```

## Self-Contained JavaScript Source

Call `runCleanUtilsTool(userInput)` with the user's input. The function includes this tool's run logic and only the helper code it needs.

```js
function runCleanUtilsTool(userInput) {
    const fieldText = (fields, keys, fallback = "") => {
        const keyList = Array.isArray(keys) ? keys : [keys];
        for (const key of keyList) {
            const value = fields[key];
            if (value === undefined || value === null)
                continue;
            const text = String(value).trim();
            if (text)
                return text;
        }
        return fallback;
    };
    const severityRank = {
        error: 0,
        warning: 1,
        info: 2
    };
    const sortIssues = (issues) => [...issues].sort((a, b) => {
        const severity = severityRank[a.severity] - severityRank[b.severity];
        if (severity !== 0)
            return severity;
        return (a.line ?? a.row ?? 0) - (b.line ?? b.row ?? 0);
    });
    const summarizeIssues = (issues) => {
        const errors = issues.filter((issue) => issue.severity === "error").length;
        const warnings = issues.filter((issue) => issue.severity === "warning").length;
        const infos = issues.filter((issue) => issue.severity === "info").length;
        const parts = [];
        if (errors)
            parts.push(`${errors} error${errors === 1 ? "" : "s"}`);
        if (warnings)
            parts.push(`${warnings} warning${warnings === 1 ? "" : "s"}`);
        if (infos)
            parts.push(`${infos} note${infos === 1 ? "" : "s"}`);
        return parts.length ? parts.join(", ") : "No issues found";
    };
    const parseEnvText = (input) => {
        const env = {};
        input.split(/\r?\n/).forEach((line) => {
            const match = line.match(/^\s*([A-Za-z_][A-Za-z0-9_]*)\s*=\s*(.*)\s*$/);
            if (match)
                env[match[1]] = match[2].replace(/^["']|["']$/g, "");
        });
        return env;
    };
    const previewDockerComposeEnvInterpolation = (input) => {
        const compose = fieldText(input, "compose");
        const env = parseEnvText(fieldText(input, "env"));
        const issues = [];
        const resolved = compose.replace(/\$\{([A-Za-z_][A-Za-z0-9_]*)(?:(:-|-|\?)([^}]*))?\}/g, (_match, key, operator, fallback) => {
            if (env[key] !== undefined && env[key] !== "")
                return env[key];
            if (operator === ":-" || operator === "-")
                return fallback ?? "";
            if (operator === "?") {
                issues.push({ severity: "error", message: `${key} is required for interpolation.` });
                return "";
            }
            issues.push({ severity: "warning", message: `${key} is not defined; substituted an empty string.` });
            return "";
        });
        return {
            summary: `Compose interpolation preview complete. ${summarizeIssues(issues)}.`,
            issues: sortIssues(issues),
            output: resolved,
            exportFilename: "compose.resolved.yml",
            stats: { envKeys: Object.keys(env).length }
        };
    };
    const __userInput = userInput == null ? {} : userInput;
    const __run = (fields) => previewDockerComposeEnvInterpolation(fields);
    const __fields = __userInput && typeof __userInput === "object" && "fields" in __userInput && __userInput.fields && typeof __userInput.fields === "object" && !Array.isArray(__userInput.fields)
        ? __userInput.fields
        : (__userInput && typeof __userInput === "object" && !Array.isArray(__userInput) ? __userInput : {});
    const __normalizedFields = Object.fromEntries(Object.entries(__fields).map(([key, value]) => [key, value == null ? "" : (["string", "number", "boolean"].includes(typeof value) ? value : String(value))]));
    return __run(__normalizedFields);
}
```

## Checks

- Compose body and env sections: Compose YAML and env values are separated so interpolation can be previewed locally.
- Default operators: Common default forms such as VAR:-fallback are resolved when an env value is blank or missing.
- Required variables: Required variable markers are reported as errors when no value is supplied.
- Undefined variables: Unset variables without defaults are reported and substituted with an empty string.
- Preview scope: The tool previews string interpolation only; it does not run Docker Compose or validate full YAML semantics.

## Related Tools

- [.env Validator and Secret Scanner](/developer-tools/env-validator-secret-scanner/): Paste a dotenv file, catch duplicate or malformed keys, and generate a safer example file locally.
- [.env Diff and Missing Key Checker](/developer-tools/env-diff-missing-key-checker/): Compare two dotenv snapshots and report missing, extra, or changed environment keys.