> ## Documentation Index
> Fetch the complete documentation index at: https://docs.pidgeon.health/llms.txt
> Use this file to discover all available pages before exploring further.

# Get started with Post

> Generate an HL7 message, validate it against the published spec, check FHIR conformance, and export the proof. Free generation and validation, no account required.

Post generates, validates, and delivers test messages: HL7 v2.3 through v2.8, FHIR R4, and NCPDP SCRIPT. Validation is derived from the published standard's machine-readable definitions, so the generator and validator can't drift from the spec or from each other.

Free generation and validation work without an account. Pro features require a Pidgeon account sign-in.

## Before you start

* [Install Post](/getting-started/install-windows) (or on [macOS](/getting-started/install-macos)).
* Post runs its engine in a local Bridge sidecar on `localhost:5101`. It starts with the app; you don't manage it separately.

## One loop: generate, validate, prove

<Steps>
  <Step title="Generate a message">
    Open the **Generate** panel (under **Compose** in the sidebar). Pick a message type, for example `ADT^A01`, set a count, and generate. The message appears in the output pane with syntax highlighting.

    The same operation from the CLI:

    ```bash theme={null}
    pidgeon generate ADT^A01 --count 10 --output admissions.hl7
    ```
  </Step>

  <Step title="Validate it">
    Open the **Validate** panel (under **Inspect**). Paste your generated message or load the file, then choose a mode: **strict** (the published spec) or **compatibility** (real-world tolerance). Results show field-level issues with rule IDs, expected/actual values, and a fix suggestion per issue.

    CLI equivalent:

    ```bash theme={null}
    pidgeon validate --file admissions.hl7 --mode strict
    ```

    Exit code `0` means validation passed; `1` means issues were found. That makes it a CI gate with no extra wiring.
  </Step>

  <Step title="Inspect a field you don't recognize">
    Every validation issue links into the built-in standards reference. You can also look up any segment or field directly:

    ```bash theme={null}
    pidgeon lookup PID.3
    ```
  </Step>

  <Step title="Run a conformance check">
    Open the **Conformance** panel (under **Inspect**) to probe a FHIR endpoint against a published Implementation Guide and read the pass/fail result per rule. Current IG scope includes US Core and Da Vinci PAS 2.1.

    CLI equivalent:

    ```bash theme={null}
    pidgeon conform --endpoint https://api.example.org/fhir --ig davinci-pas-2.1 --ci
    ```
  </Step>

  <Step title="Export the proof">
    Open **Reports** (under **Library**) to export validation and conformance results as self-contained HTML you can attach to a ticket or hand to a stakeholder.
  </Step>
</Steps>

## When something fails

| What you see                                                                     | What it means                                                                               | Next action                                                                                                                       |
| -------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------- | --------------------------------------------------------------------------------------------------------------------------------- |
| Status bar pill shows **Offline**, and panels report "Pidgeon Bridge is offline" | The local engine sidecar isn't reachable. Generation and validation run on it.              | Open **Settings → Connection** and retry. The connection tab shows the port (`5101`) and live status.                             |
| Validation issues with rule IDs (for example `HL7-REQ-002`)                      | Your input message has a problem; this is the product working, not an error state           | Each issue carries an expected/actual pair and a fix suggestion. Use the `pidgeon lookup` tip on the issue to open the reference. |
| A message type or version combination is marked unsupported                      | Post signals capability per message type and version rather than emitting a partial message | Pick a supported type/version pair from the picker, or check [Message Generation](/post/message-generation) for what's covered.   |

## Next steps

* [Message generation in depth](/post/message-generation)
* [Validation modes](/post/validation)
* [CLI quickstart](/getting-started/quickstart-cli)