Category · Voice & speech
Conversational voice-agent APIs
Platforms that run a spoken conversation for you, either with one speech-to-speech model or a configurable pipeline of speech-to-text, a language model and text-to-speech. Compared on response latency, handling interruptions, tool calls, recovery after a misunderstanding and cost per completed call.
Capability keys voice.agent · voice.speech-to-speech · voice.pipeline · voice.tools · voice.telephony · All tools
letme.dev/voice.agent picks the top-graded tool in this list and says how to call it direct; calling through letme comes later.
The same listing from the live API. Graded results come first, then the official MCP registry when no graded-only filter is set.
https://www.anchorterminal.com/api/v1/searchFilters
| Compare | # | Tool | Category | Grade | Score | Agent rating | p95 | Context | Price / x402 | Auth | Where | Details |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 83 | ElevenLabs Agents API + MCPElevenLabs · HTTP API | Voice agents | BB | 71.5 | 3.5 (2) | n/a | n/a | $22 / mo | OAuth or key | Hosted | ||
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ElevenAgents (formerly Conversational AI) runs hosted voice agents as a pipeline of a fine-tuned ElevenLabs ASR model, an LLM of your choice or your own, ElevenLabs TTS and a proprietary turn-taking model. Top strength API keys scoped to endpoint groups, with per-key credit limits and service accounts Top weakness $0.08 a minute excludes LLM tokens and carrier minutes |
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| 114 | Retell AI API + MCPRetell AI · HTTP API | Voice agents | B | 69.4 | 3.5 (2) | n/a | n/a | $2 / mo | API key | Hosted | ||
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Hosted platform for phone and web voice agents, built as single-prompt agents or node-based conversation flows. Top strength Published per-minute price for every component, from $0.07 a minute all in Top weakness Call data kept indefinitely unless retention is set per agent |
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| 126 | Deepgram Voice Agent APIDeepgram · HTTP API | Voice agents | B | 68.4 | 3.0 (2) | n/a | n/a | Pay per use | API key | Hosted + local | ||
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One WebSocket that runs Deepgram STT (Flux or Nova-3), a managed or bring-your-own LLM and Deepgram or third-party TTS, with turn-taking, barge-in and function calling. Top strength $0.075 a minute all in on Standard, $0.050 with your own LLM and TTS, $200 of credit with no card Top weakness No phone numbers or SIP, so you bridge Twilio or another carrier yourself |
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| 191 | Bland AI API + MCPBland AI · HTTP API | Voice agents | B | 64.1 | 3.0 (2) | n/a | n/a | $299 / mo | API key | Hosted + local | ||
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Phone-first voice-agent platform that runs its own speech recognition, language model, TTS and telephony, billed as one per-minute rate. Top strength One per-minute rate covering STT, LLM, TTS and telephony, $0.14 on Start and $0.12 on Build Top weakness No OpenAPI document |
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| 198 | Vapi API + MCPVapi · HTTP API | Voice agents | B | 63.7 | 2.5 (2) | n/a | n/a | $29 / mo | API key | Hosted + local | ||
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Developer platform for phone and web voice agents. Top strength Any mix of transcriber, model and voice provider, or your own keys and endpoints Top weakness Real per-minute cost depends on provider choices |
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| 279 | Ultravox Realtime APIUltravox (Fixie.ai) · HTTP API | Voice agents | C | 58.6 | 3.0 (2) | n/a | n/a | $100 / mo | API key | Hosted | ||
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Hosted voice agents on Ultravox, an open-weight model that takes speech directly with no speech-to-text step and answers through a TTS voice. Top strength Flat $0.05 a minute including model and built-in voices Top weakness No MCP server |
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| 296 | Hume EVI (Empathic Voice Interface)Hume AI · HTTP API | Voice agents | C | 57.3 | 2.0 (2) | n/a | n/a | $14 / mo | OAuth or key | Hosted | ||
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Hume's hosted voice-agent service, accessed through a WebSocket API. Top strength Speech-language model that reads the caller's tone and answers with matching prosody Top weakness One account-wide key, sent in the WebSocket and Twilio webhook URLs |
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| 339 | Bolna API + MCPBolna · HTTP API | Voice agents | D | 52.9 | 2.5 (2) | n/a | n/a | Pay per use | API key | Hosted | ||
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Voice-agent platform built for Indian languages and phone campaigns. Top strength Transcriber, LLM and voice chosen per agent, or one OpenAI Realtime or Gemini Live model Top weakness Unsigned webhooks and tool calls, IP allowlisting only |
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| 352 | Synthflow API + MCPSynthflow · HTTP API | Voice agents | D | 51.3 | 2.0 (2) | n/a | n/a | Paid | OAuth or key | Hosted | ||
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Enterprise voice-agent platform built around a no-code Flow Designer and prompt builder, with a REST Platform API and a hosted MCP server. Top strength Changelog entries almost daily, ten between 7 September and 1 October 2026 Top weakness Sales-led only, contracts from $30,000 a year, no free tier |
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| 383 | Vogent APIVogent · HTTP API | Voice agents | D | 47.4 | 2.0 (2) | n/a | n/a | Pay per use | API key | Hosted | ||
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Phone voice-agent platform with its own conversational LLM, voices and IVR-navigation models alongside GPT. Top strength IVR detection and navigation models for outbound calls Top weakness No public changelog and no release found since January 2026 |
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Nothing matches these filters. .
p95 latency and context cost come from our probes, which haven't run yet, so those columns start hidden. Grades run from AA to F, and agent-ready means BB or better. Filters, sorting and export run in your browser; the table is complete without JavaScript.
Indexed, not reviewed (1)
Listings sorted into this category from public catalogues (the official MCP registry, APIs.guru, the x402 Bazaar and OpenRouter), with facts and our own checks but no score, grade or rank. How the index works.
| Listing | Kind | What it does | Why it's here |
|---|---|---|---|
| callwright topness.com | MCP server | Self-hosted MCP voice agent that places phone calls on your behalf via Retell. | vendor's own |
How we test this category
The same booking and support tasks on every platform. We measure response latency, how interruptions are handled, tool-call success, recovery after a misunderstanding and the total cost per completed call, and record whether the product runs a direct speech-to-speech model or an STT, model and TTS pipeline, since those are different setups. This test hasn't run yet, so Task success is pending and the grades here come from the categories assessed from public evidence.
How the ranking works
Every listing is scored 0 to 100 and given a grade from AA to F. In the October 2026 research run, 7 of the 9 weighted categories are scored from public evidence (status history, docs, pricing, terms, source and security pages) against a published checklist, with the reason and sources for every score on the listing. Performance and Task success wait for our probes and task suites, so their weight is shared across the rest until they run. Negative events deduct up to 15 points. Read the methodology.
For companies
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