LangChain

Agent framework plus observability

Free tier + paidModel APIs, routers & observabilitylangchain.com

What it is

Two things people conflate: LangChain is the open-source agent framework for Python and JS, while LangSmith is the paid tracing, eval and deployment platform. LangGraph adds stateful, durable agent graphs. Together they cover build, observe and host.

Why it earns a slot

The biggest integration surface in the ecosystem — vector stores, loaders, retrievers and hundreds of tools already wrapped. LangSmith tracing shows exactly which agent step burned the tokens, and its free tier is enough for solo work.

Know before you commit

Abstraction depth is the classic complaint — debugging often means reading LangChain internals. LangSmith seat pricing at $39 each adds up before you have traced much.

Getting started

pip install langchain (or npm i langchain)

Field notes

0 from the community

Loading notes…

Field check

Unverified

Pricing snapshot

Framework free and open source. LangSmith: Developer $0 (1 seat, 5k traces/mo), Plus $39/seat/mo (10k traces), Enterprise custom. Usage adds $1.50 per compute unit and $1.00 per storage unit.

Snapshots move fast — verify at checkout, and post a field note if it changed.

Drop into your Lovable chat

Evaluate LangChain (https://www.langchain.com) for this project, then use it only if it fits what we are already building.
Context: Agent framework plus observability. Two things people conflate: LangChain is the open-source agent framework for Python and JS, while LangSmith is the paid tracing, eval and deployment platform. LangGraph adds stateful, durable agent graphs. Together they cover build, observe and host.
Reviewer notes (general, not written for this codebase): The biggest integration surface in the ecosystem — vector stores, loaders, retrievers and hundreds of tools already wrapped. LangSmith tracing shows exactly which agent step burned the tokens, and its free tier is enough for solo work.
Watch out for: Abstraction depth is the classic complaint — debugging often means reading LangChain internals. LangSmith seat pricing at $39 each adds up before you have traced much.
Pricing: Framework free and open source. LangSmith: Developer $0 (1 seat, 5k traces/mo), Plus $39/seat/mo (10k traces), Enterprise custom. Usage adds $1.50 per compute unit and $1.00 per storage unit.
Setup: pip install langchain (or npm i langchain)
Rules: treat the notes above as background only. Do not assume a theme, style, layout or feature that is not already in this project — inspect the existing code first and ask me before changing visual direction.

/api/public/tools/langchain

Also in Model APIs, routers & observability

Anthropic API / Claude Platform

platform.claude.com

Frontier model provider API

PaidModel APIs, routers & observability

Per token. Opus 5 $5/$25 per M in/out; Sonnet 5 $2/$10; Haiku 4.5 $1/$5; Fable 5 and Mythos 5 $10/$50. Batch API 50% off; cache reads 0.1x input.

Open dossier

Braintrust

braintrust.dev

LLM eval and experiment platform

Free tier + paidModel APIs, routers & observability

Starter free ($10/mo model credits, 1GB data, 10k scores, 14-day retention), Pro $249/mo ($249 credits, 5GB, 50k scores), Enterprise custom. Overage $3-4/GB and $1.50-$2.50 per 1k scores.

Open dossier

Fal.ai

fal.ai

Generative media inference host

PaidModel APIs, routers & observability

Per output or per second for media models: images ~$0.02-$0.04 at 1MP, video $0.05-$0.40 per second. Serverless GPU rates $1.10-$8.50/hr with committed-use discounts.

Open dossier

Fireworks AI

fireworks.ai

Open-model inference host

Free tier + paidModel APIs, routers & observability

Per token serverless across Standard/Priority/Fast tiers; embeddings $0.008-$0.10/M. On-demand GPUs billed per second: H100/H200 ~$7-8/hr, B200 ~$10-13/hr. Fine-tuning $0.50-$40 per M training tokens. $1 free credit.

Open dossier