splera-mcp
A/B testing for vibe coders, exposed as a Model Context Protocol (MCP) server. Your AI agent creates experiments, reads results, and ships winners without you leaving chat.
Three native tools your agent gets once installed: create_experiment, get_results, ship_winner. The agent calls them, edits your code to wire the SDK and variant, and reports stats back in plain English. No dashboard tab, no copy-paste, no test infrastructure to learn.
What you can do
Once installed, paste any of these into your agent:
Create a Splera A/B test for my homepage headline: 'Ship faster.' vs 'Ship with confidence.'
How's my checkout experiment doing?
Ship the winning variant.
The agent picks the right tool, makes the call, and either edits your code to install the SDK, reports Bayesian stats in human terms, or flips the winning variant server-side (takes effect in ~30 seconds worldwide, no redeploy).
Install
1. Generate an API key
Go to splera.ai/settings, click Generate new key, name it something like claude-code-macbook. Copy the key from the one-time modal. It starts with splera_live_. You will not see the full key again. If you close the modal without copying, revoke and regenerate.
2. Add the config to your agent
| Agent | Config file | Method |
|---|
| Claude Code | ~/.config/claude-code/mcp.json | One-liner (below) or edit JSON |
| Cursor | ~/.cursor/mcp.json | Edit JSON (or Settings → MCP) |
| Windsurf | ~/.codeium/windsurf/mcp_config.json | Edit JSON |
| Zed | ~/.config/zed/settings.json (context_servers block) | Edit JSON |
| Replit Agent | Not supported in v1 (cloud-hosted, can't load local stdio MCP) | — |
Claude Code
claude mcp add splera npx -y splera-mcp@latest --env SPLERA_API_KEY=splera_live_your_key_here
Then restart Claude Code.
Cursor / Windsurf
Same JSON shape for both, just different file paths.
{
"mcpServers": {
"splera": {
"command": "npx",
"args": ["-y", "splera-mcp@latest"],
"env": {
"SPLERA_API_KEY": "splera_live_your_key_here"
}
}
}
}
Restart the agent.
Zed
Add to ~/.config/zed/settings.json:
{
"context_servers": {
"splera": {
"command": {
"path": "npx",
"args": ["-y", "splera-mcp@latest"],
"env": { "SPLERA_API_KEY": "splera_live_your_key_here" }
}
}
}
}
Restart Zed.
Verify your install
Option A: check the key from any terminal
curl -H "Authorization: Bearer splera_live_your_key_here" https://splera.app/api/me
200 OK with a JSON body means the key works. 401 means the key is bad or revoked, regenerate at splera.ai/settings.
Option B: check the agent's MCP panel after restart
Open your agent's Server logs or MCP panel. You should see:
splera-mcp: connecting to https://splera.app
splera-mcp: ready. 3 tools loaded. User: [email protected]
If those lines are missing, the MCP isn't loading. Check your config file path and JSON syntax.
Troubleshooting
"splera is not available" / "tool not found"
The MCP config isn't being read. Check that (1) you edited the right file for your agent (see install table above), (2) the JSON is valid, no trailing commas, (3) you restarted the agent after editing.
SPLERA_API_KEY not set / SPLERA_API_KEY_MISSING on every call
The server starts without a key (so your agent still lists the tools), but every call fails until the key is set. The env block in your MCP config is missing or malformed. The key must start with splera_live_. Re-check the examples above.
401 / SPLERA_INVALID_API_KEY on every call
The key is wrong, revoked, or truncated during copy. Go to splera.ai/settings, revoke the existing key, generate a new one, update the config, restart the agent.
SPLERA_PLAN_LIMIT_EXCEEDED on create_experiment
You've hit your plan's monthly experiment cap. Options: upgrade or ship / stop an existing experiment to free a slot. The error hint field tells you which plan and how many slots are used.
get_results says NOT_READY forever
The SDK isn't reaching the page being tested. Verify the script tag is in place:
<script src="https://splera.app/sdk/splera.js"
data-experiment="YOUR-EXPERIMENT-UUID"
data-api-url="https://splera.app"></script>
data-api-url is required: without it the SDK tracks nothing. If your experiment was created with splera-mcp 0.1.1, its install code was missing this attribute and used a callback form of getVariant that never runs. Re-copy the snippet from the experiment page on the dashboard.
Also confirm the page is receiving real traffic. The dashboard shows live exposure counts at splera.ai/experiments/:id.
Agent doesn't use the Splera tool even when I ask
Most agents need explicit mentions of the tool until it's familiar. Try prompts like "use the splera MCP to create an experiment" instead of generic "set up an A/B test". Once the agent calls it once, it remembers.
Tool reference
create_experiment
Create a new A/B test. Returns the experiment ID, variant IDs, and an SDK install snippet the agent can paste into your codebase.
Required: name (3-80 chars), hypothesis (10-500 chars), variants (2-5 items, control first), metrics (1-5 items, each with name + event_name).
Optional: decision_mode (quick_decision / rigorous / bandit, default quick_decision), platform (replit / lovable / bolt / claude_design / other, default other).
Example prompt:
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