# Variables API

The Variables API is a fast key-value store for ephemeral state. Unlike
memories (which are indexed, searchable, and structured), variables are
optimized for quick read/write access — perfect for counters, flags, and
session state.

## Endpoints

### POST /var

Set or update a variable.

```bash
curl -X POST https://synapse.schaefer.zone/var \
  -H "Authorization: Bearer YOUR_MIND_KEY" \
  -H "Content-Type: application/json" \
  -d '{"key": "last_session_at", "value": "2026-06-27T14:00:00Z"}'
```

### GET /var/:key

Get a single variable.

```bash
curl -H "Authorization: Bearer YOUR_MIND_KEY" \
     https://synapse.schaefer.zone/var/last_session_at
```

Response:

```json
{ "key": "last_session_at", "value": "2026-06-27T14:00:00Z", "updated_at": "..." }
```

### GET /var

List all variables.

```bash
curl -H "Authorization: Bearer YOUR_MIND_KEY" \
     https://synapse.schaefer.zone/var
```

### DELETE /var/:key

Delete a variable.

```bash
curl -X DELETE -H "Authorization: Bearer YOUR_MIND_KEY" \
     https://synapse.schaefer.zone/var/last_session_at
```

## When to Use Variables vs Memory

| Use Case | Use |
|----------|-----|
| User name, preferences | Memory (searchable, structured) |
| Last session timestamp | Variable (ephemeral state) |
| Counter (e.g. messages sent) | Variable (frequent updates) |
| Workflow state ("step 3 of 5 done") | Variable (transient) |
| Long-form project notes | Memory (full-text indexed) |
| Reusable scripts | Script store (named, versioned) |

## Common Patterns

### Track last session

```bash
# At session end
curl -X POST .../var -d '{"key": "last_session_at", "value": "'$(date -Iseconds)'"}'

# At session start
LAST=$(curl .../var/last_session_at | jq -r .value)
curl .../memory/diff?since=$(date -d "$LAST" +%s)
```

### Counter pattern

```bash
# Increment
N=$(curl .../var/api_calls | jq -r .value)
curl -X POST .../var -d "{\"key\": \"api_calls\", \"value\": $((N+1))}"
```

### Feature flags

```bash
curl -X POST .../var -d '{"key": "feature_x_enabled", "value": "true"}'

# Check
ENABLED=$(curl .../var/feature_x_enabled | jq -r .value)
if [ "$ENABLED" = "true" ]; then ... fi
```

## Next Steps

- [Memory API](/docs/api/memory) — for structured, searchable data
- [Cron & Scheduler](/docs/api/cron)