Verify App Behavior with stably verify Skill

Verify App Behavior with stably verify

stably verify checks whether your application works correctly by describing expected behavior in plain English. It launches an AI agent that navigates your app in a real browser, interacts with it, takes screenshots, and reports a structured PASS / FAIL / INCONCLUSIVE verdict. No test files are generated.

Pre-flight

Always run stably --version first. If not found, install with npm install -g stably or use npx stably. Requires Node.js 20+ and a Stably account.

stably --version
echo "STABLY_API_KEY: ${STABLY_API_KEY:+set}"
echo "STABLY_PROJECT_ID: ${STABLY_PROJECT_ID:+set}"

Usage

# Verify a feature works
stably verify "the login form accepts email and password and redirects to /dashboard"

# With a specific starting URL
stably verify "the pricing page shows 3 tiers" --url http://localhost:3000/pricing

# Set a budget cap (default: $5)
stably verify "checkout flow completes successfully" --max-budget 10

# Non-interactive mode (for CI or background agents)
stably verify "checkout flow completes" --no-interactive

# Use cloud browser instead of local
stably verify "login works" --browser cloud

Options

| Option | Description | |--------|-------------| | -u, --url <url> | Starting URL (auto-detected from localhost if omitted) | | --max-budget <dollars> | Budget cap in USD (default: 5) | | --no-interactive | Skip preflight prompts | | --browser <type> | Browser type: local or cloud (default: local). Also settable via STABLY_CLOUD_BROWSER=1 |

Exit Codes

| Code | Verdict | Meaning | |------|---------|---------| | 0 | PASS | All requirements verified | | 1 | FAIL | One or more requirements not met | | 2 | INCONCLUSIVE | Cannot determine (app unreachable, auth wall, etc.) |

Iteration Loop

After making code changes, use stably verify to check the feature:

Run verify — stably verify "description of expected behavior"
If FAIL — Read the failure reason and evidence from the output
Fix code — Modify your application code based on the failure
Re-verify — Run the same stably verify command again
Repeat until PASS

stably verify does not create or modify any files. It only observes and reports. Fix the code yourself based on its findings.

Composing in Scripts

# Gate on verification
stably verify "login works" && echo "Feature verified!"

# Handle all three outcomes
stably verify "checkout completes" ; code=$?
if [ $code -eq 0 ]; then echo "PASS";
elif [ $code -eq 1 ]; then echo "FAIL";
else echo "INCONCLUSIVE"; fi

Long-Running Commands (AI Agents)

stably verify is AI-powered and can take several minutes depending on complexity.

| Agent | Configuration | |-------|--------------| | Claude Code | timeout: 600000 on Bash tool | | Cursor | block_until_ms: 900000 |

Links

Docs · Verify Guide · CLI Quickstart · Dashboard

Agent Skills: Verify App Behavior with stably verify

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