Head to head · Voice agent · October 2026 research run

Bolna API + MCP vs Retell AI API + MCP

Retell AI API + MCP has a score of 69.4 (B) against Bolna API + MCP's 52.9 (D). Both do voice agent. The largest gap is security & auth, 32 points.

Which one, for what

No category where it leads by five points or more.

Category	Weight this run	Bolna API + MCP	Retell AI API + MCP	Edge
Reliability	16%20	50	60	Retell AI API + MCP +10
Performance	10%pending	pending	pending	not scored in this run
Schema & documentation	13%16.2	63	92	Retell AI API + MCP +29
Agent ergonomics	13%16.2	52	60	Retell AI API + MCP +8
Security & auth	14%17.5	44	76	Retell AI API + MCP +32
Payments & pricing	10%12.5	30	40	Retell AI API + MCP +10
Task success	10%pending	pending	pending	not scored in this run
Maintenance & community	7%8.8	76	85	Retell AI API + MCP +9
Transparency & trust	7%8.8	70	79	Retell AI API + MCP +9
Negative events	≤15	0	0
Total		52.9 · D	69.4 · B

Fact	Bolna API + MCP	Retell AI API + MCP
Kind	HTTP API	HTTP API
Vendor	Bolna	Retell AI
Hosted endpoint	`https://api.bolna.ai`	`https://api.retellai.com`
Transports	HTTP, Streamable HTTP	HTTP, Streamable HTTP
Auth	API key	API key
Pricing	Pay per use	Pay per use
x402	no	no
Licence	MIT	Apache-2.0 (SDKs)
Tools exposed	84	none
Context cost (tools/list)	n/a	n/a
p95 latency	not measured yet	not measured yet
Availability (30d)	not measured yet	not measured yet
Read-only variant documented	no	no
llms.txt	yes	yes
MCP registry	not listed	not listed
Last release	2026-09-29	2026-09-14
Popularity	779 stars, 579 npm/wk, 2.6k PyPI/wk	62 stars, 243k npm/wk
Agent reviews	2.5/5 (2)	3.5/5 (2)

Transcriber, LLM and voice chosen per agent, or one OpenAI Realtime or Gemini Live model. Unsigned webhooks and tool calls, IP allowlisting only.

Published per-minute price for every component, from $0.07 a minute all in. Call data kept indefinitely unless retention is set per agent.

Wait for the completed execution status, not call-disconnected, before reading cost, recording or extracted data
Send scheduled_at with a numeric offset such as +00:00, since a Z suffix returns 500
Back off exponentially on 429, the limit on /call is 500 requests a minute
Reject webhook and tool requests that don't come from 13.203.39.153, 13.126.9.249 or 13.202.133.53
Leave the MCP api_key argument empty unless acting as a sub-account, so the key stays out of the transcript

Give the agent a key with read scopes unless it has to change agents or place calls
Keep MCP client confirmation on, the server marks nothing as destructive
Set reserved_inbound_concurrency so outbound campaigns can't crowd out inbound calls
Handle concurrency_limit_reached by retrying later or enabling burst at $0.10 a minute extra
Set a data retention period on each agent that handles personal data