The 9 best AI agent builders for developers (2026)

As of October 2026, Gumloop has the lowest paid entry price here, from $37/month. 7 have a free plan.

Updated 24 October 20269 agents2 verified in the last 30 days7 updated in that window

Prices checked 9 September–24 October 2026

Reviewed by The Agents Index editorial team.

The ones whose price, API, docs, sources and limits we could confirm come first. How we rank →

This spot is open
Featured agents show here and first on related and alternatives pages.
- API access: Not stated
- Free tier: Not stated
- MCP server: Not stated
- Own API key: Not stated
- Open source: Not stated
- Self-hosted: Not stated
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Letta
Stateful agent harness, cloud and SDK for agents with persistent, git-versioned memory.
Free, then $20/month
From
Free, then $20/month
- API access: Yes
- Free tier: Yes
- MCP server: No
- Own API key: Yes
- Open source: Yes
- Self-hosted: Yes
Checked 2 September 2026
Visit LettaCompare Letta
Sim
Verified
Open-source AI workspace for building, deploying and running agents across 1,000+ integrations.
Free, then $25/seat/month
From
Free, then $25/seat/month
- API access: Yes
- Free tier: Yes
- MCP server: Yes
- Own API key: Yes
- Open source: Yes
- Self-hosted: Yes
Checked 3 September 2026
Visit SimCompare Sim
MindStudio
No-code platform for building, running and deploying AI agents as drag-and-drop workflows.
Free, then $20/month
From
Free, then $20/month
- API access: Yes
- Free tier: Yes
- MCP server: Yes
- Own API key: Yes
- Open source: Partly
- Self-hosted: Partly
Checked 20 September 2026
Visit MindStudioCompare MindStudio
Dify
Open-source platform for building agentic workflows, AI agents and RAG knowledge pipelines.
Free, then $59/month
From
Free, then $59/month
- API access: Yes
- Free tier: Yes
- MCP server: Yes
- Own API key: Yes
- Open source: Yes
- Self-hosted: Yes
Checked 2 September 2026
Visit DifyCompare Dify
Relevance AI
Platform for building and running specialist business agents and multi-agent workforces.
On quote
From
On quote
- API access: Yes
- Free tier: Partly
- MCP server: Yes
- Own API key: Yes
- Open source: Not stated
- Self-hosted: No
Checked 22 September 2026
Visit Relevance AICompare Relevance AI
Agno
Python SDK, self-hosted AgentOS runtime and hosted control plane for running agents as a service.
Free, then $150/month
From
Free, then $150/month
- API access: Yes
- Free tier: Yes
- MCP server: Yes
- Own API key: Yes
- Open source: Partly
- Self-hosted: Yes
Checked 17 October 2026
Visit AgnoCompare Agno
Gumloop
Multiplayer AI agent builder: teams build agents over their apps while IT keeps governance and spend control.
From $37/month
From
$37/month
- API access: Yes
- Free tier: Partly
- MCP server: Yes
- Own API key: Yes
- Open source: Not stated
- Self-hosted: Partly
Checked 30 September 2026
Visit GumloopCompare Gumloop
Pickaxe
No-code platform for building AI agents and selling them through branded portals with billing built in.
Free, then $37/month
From
Free, then $37/month
- API access: Partly
- Free tier: Yes
- MCP server: Yes
- Own API key: No
- Open source: Not stated
- Self-hosted: Not stated
Checked 9 September 2026
Visit PickaxeCompare Pickaxe
StackAI
No-code enterprise platform for building, deploying and governing AI agents across business systems.
Free
From
Free
- API access: Partly
- Free tier: Yes
- MCP server: Yes
- Own API key: Yes
- Open source: No
- Self-hosted: Partly
Checked 9 September 2026
Visit StackAICompare StackAI
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9 agents in Agent builders
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- Every fact sourced to your own pages
- Edit it from your dashboard
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Open-source and hosted builders where you assemble agents from models, tools and your data, then deploy them.

Questions buyers ask

Which agent here costs the least?

Agno, Dify and Letta and 4 more have a free plan. The lowest paid plan is Gumloop, from $37/month. Price checked on 24 October 2026.

Which agents here have a free plan?

7 of the 9: Agno, Dify, Letta, MindStudio and Pickaxe and 2 more.

When were these prices checked?

Between 9 September 2026 and 24 October 2026, each read on the maker's own pricing page.

Sources and method

How we rank

Every price here was read on the maker's own pricing page.

Agno: agno.com/pricing, checked 17 October 2026
Dify: dify.ai/pricing, checked 24 October 2026
Gumloop: gumloop.com/pricing, checked 24 October 2026
Letta: docs.letta.com/pricing, checked 24 October 2026
MindStudio: mindstudio.ai/pricing, checked 24 October 2026
Pickaxe: pickaxe.co/pricing, checked 9 September 2026
Relevance AI: relevanceai.com/pricing, checked 24 October 2026
Sim: sim.ai/pricing, checked 24 October 2026
StackAI: stackai.com/pricing, checked 9 September 2026

All Agent builders

Letta

Sim

MindStudio

Dify

Relevance AI

Agno

Gumloop

Pickaxe

StackAI

Questions buyers ask

Which agent here costs the least?

Which agents here have a free plan?

When were these prices checked?

Sources and method