Relay vs MCP Server
A side-by-side look at the Relay and MCP Server MCP servers: transport, auth, tools, quality signals, and the config to install either one in Claude, Cursor, Windsurf or VS Code.
Verdict: choose Relay for conversational ai work as a local process; choose MCP Server for conversational ai as a local process. You can also run both side by side in one mcpServers block.
Which MCP server should you choose?
Choose Relay when
- You need dedicated capabilities in the Conversational AI domain.
- You prefer a local stdio subprocess transport.
- You have the keys it needs:
RELAY_API_KEY, RELAY_BASE_URL. - You want tools like
search_models, get_model, get_pricing.
Choose MCP Server when
- You need dedicated capabilities in the Conversational AI domain.
- You prefer a local stdio subprocess transport.
- Its auth model fits you: API key required.
- You have the keys it needs:
VAPI_TOKEN. - You want tools like
list_assistants, create_assistant, get_assistant.
Feature & specification comparison
Rows where the two servers differ are marked.
| Spec | ||
|---|---|---|
| Category | Conversational AI | Conversational AI |
| Quality signal | 61/100 · Good | 68/100 · Great |
| Install command | Confirmed | Confirmed |
| Transport | Local subprocess (stdio) | Local subprocess (stdio) |
| Auth | Not declared | API key required |
| Pricing | Not declared | BYOK (pay the provider) |
| Required env vars | RELAY_API_KEYRELAY_BASE_URL | VAPI_TOKEN |
| Verified owner | Community listing | Community listing |
| GitHub stars | 0 | 58 |
| Directory activity | 1 views 0 installs 0 upvotes | 1 views 0 installs 0 upvotes |
| Tools | 14 | 13 |
| Full listing | View Relay | View MCP Server |
Tools & capabilities
Relay tools 14
search_modelsLists Relay models by tag and/or text. Common tags: text-to-image, image-to-image, text-to-video, image-to-video, video-to-video, text-to-speech, speech-to-text, text-to-text, text-to-embedding. image-to-image also lists every image model that takes an input image. Returns name, tag, route and accepts (input media the model takes, e.g. ["image"]; [] for none) per model (at most 50). Then call get_model with a name for its input schema.get_modelReturns one model's route, request_schema (what run_model's input must follow), request_example, pricing and availability. Then call run_model with an input shaped like request_example.get_pricingReturns Relay's public list prices (USD), optionally for one model, plus media_storage: the per-file fees of the store_output / upload retention SKUs (relay1d, relay7d, …). Then estimate_cost for a number.estimate_costEstimates the USD cost of a call from the public price list: an estimate, not an invoice (the bill uses provider-reported usage and any custom pricing on your account). Pass only the usage fields the model's billing_type (see get_model or get_pricing) reads: per_token: input_tokens, output_tokens, cached_input_tokens; per_image: image_count, resolution_tier; per_second_video: duration_seconds, quality_mode, sound; per_second_audio: duration_seconds; per_character: character_count; per_media_token: media_input_tokens, media_output_tokens. Add store_output / retention / file_count for storage fees.run_modelRuns any Relay model by name (billed to your key). input follows get_model's request_schema (request_example runs as is). Every model whose schema takes async (image, video, audio) is submitted as a task: it waits up to 45 s, past that it returns a task_id — do not resubmit, call check_task. Chat models answer inline. Result links expire 1 h after completion unless store_output names a media_storage SKU from get_pricing. Pass an idempotency_key if you may retry the same submit. Needs a Relay credential.check_taskChecks a task run_model returned (no key needed: the task_id is the capability). Waits up to 30 s for it to finish; returns the result when completed, else its status: then call check_task again, never resubmit. Task results are kept 1 h after they finish.upload_fileHosts an image, video or audio file on Relay and returns its url: pass that url to any *_url input of run_model. Give exactly one of path (local server only, ≤ 100 MB), base64 (≤ 4 MB) or url (a public link Relay copies). retention: relay1h (default, free within a daily quota) or a media_storage SKU from get_pricing. Needs a Relay credential.list_workflowsList Relay's workflow templates: multi-step pipelines (e.g. script → voiceover) run as one call. Each entry has workflow_id, input_schema and its steps (step_id + model). Run one with run_workflow; inputs follow input_schema.run_workflowStart a workflow run (one submit) and wait up to wait_seconds (≤ 45) for it to finish. Completed → the final output; still running → run_id: call check_workflow_run with it, never resubmit (a new run bills again). Each step is billed as an ordinary request. webhook_url gets ONE signed workflow.completed / workflow.failed delivery when the run ends. Get workflow_id and the inputs shape from list_workflows. Needs a Relay credential.check_workflow_runPoll a workflow run by run_id, waiting up to wait_seconds (≤ 30) for it to end. Completed → the final output; failed / cancelled → the error; still running → its steps so far: call check_workflow_run again. No key needed: the run_id is the access token.cancel_workflow_runCancel a workflow run. Cancels between steps only: a step already running completes and bills. A run that has already ended answers WORKFLOW_RUN_NOT_CANCELLABLE. Needs a Relay credential.get_creditsRead the account's credit balance, active promo credits and consumption. Needs a dashboard JWT or a custom-tier superkey; a plain inference key gets PERMISSION_DENIED (403). Needs a Relay credential.- +2 more on the listing page
MCP Server tools 13
list_assistantsLists all Vapi assistantscreate_assistantCreates a new Vapi assistantget_assistantGets a Vapi assistant by IDupdate_assistantUpdates an existing Vapi assistantlist_callsLists all Vapi callscreate_callCreates a outbound callget_callGets details of a specific calllist_phone_numbersLists all Vapi phone numbersget_phone_numberGets details of a specific phone numberlist_toolsLists all Vapi toolsget_toolGets details of a specific toolcreate_toolCreates a new Vapi tool- +1 more on the listing page
Ready-to-paste client configs
Paste either block (or both) into your client config, e.g. claude_desktop_config.json or ~/.cursor/mcp.json. We only show a config when the install command is confirmed.
Relay
{
"mcpServers": {
"relay-4": {
"command": "npx",
"args": [
"-y",
"@relaygpu/mcp"
],
"env": {
"RELAY_API_KEY": "YOUR_RELAY_API_KEY_HERE",
"RELAY_BASE_URL": "YOUR_RELAY_BASE_URL_HERE"
}
}
}
}
MCP Server
{
"mcpServers": {
"vapi-ai-mcp-server": {
"command": "npx",
"args": [
"-y",
"@vapi-ai/mcp-server"
],
"env": {
"VAPI_TOKEN": "YOUR_VAPI_TOKEN_HERE"
}
}
}
}
Frequently asked questions
Relay is categorized under Conversational AI and uses a local stdio subprocess. MCP Server belongs to Conversational AI and uses a local stdio subprocess. Pick Relay for conversational ai work and MCP Server for conversational ai.
Copy the mcpServers block from the config section on this page into your client's config (for example claude_desktop_config.json or ~/.cursor/mcp.json), then fully restart the client.
Relay has no declared pricing — check the project's own site. MCP Server is bring-your-own-key: usage is billed by the API provider you supply a key for. Auth: api key required. If a server needs environment variables such as API keys, define them under the env key in your client's MCP config.
Yes. MCP clients support multiple servers: add relay-4 and vapi-ai-mcp-server as separate keys in the same mcpServers object, and your assistant will call tools from either one.
On AllMCPs, Relay has a quality signal of 61/100 (Good) with 1 views, 0 installs and 0 GitHub stars. MCP Server has 68/100 (Great) with 1 views, 0 installs and 58 GitHub stars.