liquid-mcp
Liquid MCP is an agent-native API fabric that lets AI agents discover, connect to, and interact with any HTTP API with token-budget control, structured recovery, and pre-flight cost estimation — requiring no LLM calls at runtime after initial setup.
liquid_connect— Discover any API by URL and map it to a target data model. Handles auth-walled APIs via credentials. Returns anadapter_idfor subsequent operations. One-time setup; all future fetches are deterministic with zero LLM calls.liquid_list_adapters— List all API adapters already connected and persisted locally (~/.liquid), so agents skip redundant rediscovery.liquid_discover— Inspect an API's available endpoints and authentication requirements without creating a persistent adapter. Useful for exploration before committing to a connection.liquid_fetch— Fetch typed, structured records through a connected adapter. Fully deterministic. Returns a_metablock with service, endpoint, latency, and record count.liquid_query— Perform server-side search or aggregation to retrieve only the answer, not the full payload. Supports filtering (where), field selection,limit,group_by, and aggregation functions (e.g., sum, count). Reduces token usage by up to 98–100% vs. fetch-then-filter.liquid_estimate— Get a pre-flight estimate of expected items, bytes, tokens, credits, and latency before making any HTTP call, enabling informed budget decisions.
Enables agents to interact with Adyen's payment API through Liquid's intent layer, supporting operations like charging customers, refunding charges, customer management, and order listing with context optimization and error recovery.
Enables agents to interact with Braintree's payment API through Liquid's intent layer, supporting operations like charging customers, refunding charges, customer management, and order listing with context optimization and error recovery.
Enables agents to interact with PayPal's payment API through Liquid's intent layer, supporting operations like charging customers, refunding charges, customer management, and order listing with context optimization and error recovery.
Enables agents to interact with Shopify's API through Liquid's intent layer, supporting operations like listing orders, canceling orders, and customer management with context optimization and error recovery.
Enables agents to interact with Square's payment API through Liquid's intent layer, supporting operations like charging customers, refunding charges, customer management, and order listing with context optimization and error recovery.
Enables agents to interact with Stripe's API through Liquid's intent layer, supporting operations like charging customers, refunding charges, customer management, listing orders, and canceling orders with context optimization and error recovery.
Liquid
The agent-native API fabric.
Liquid is the transformation layer between AI agents and any HTTP API — actively optimizing for the constraints real agents hit: token budgets, context windows, cross-API cognitive load, recovery from failures, and predictable cost.
Why agents need more than a tool wrapper
Shipping an agent against real APIs surfaces problems most HTTP clients ignore:
A single
list_ordersresponse eats 50k tokens of contextStripe, Shopify, and Square represent "money" in three different shapes
A 401 from the API returns a string — the agent has to guess how to recover
Rate limits trip without warning; one agent run costs another one's budget
The agent has no way to ask "how much will this call cost me?" before making it
Liquid addresses each of these with a concrete primitive. Everything below is shipped and on PyPI.
What Liquid gives your agent
Context-budget control
# Search server-side instead of fetch-then-filter — 10-100x token savings
orders = await liquid.search(
adapter, "/orders",
where={"total_cents": {"$gt": 10000}, "status": "paid"},
limit=20,
)
# Aggregate without ever seeing records
stats = await liquid.aggregate(
adapter, "/orders",
group_by="status",
agg={"total_cents": "sum", "id": "count"},
)
# Full-text search across records (BM25-lite, ranked)
hits = await liquid.text_search(adapter, "/tickets", "shipping delay")
# Fetch only what fits in your budget
data = await liquid.fetch(adapter, "/orders", max_tokens=2000)
# -> _meta.truncated=True, _meta.truncated_at="item_42"
# Identity-plus-two-fields mode for context-constrained runs
data = await liquid.fetch(adapter, "/customers", verbosity="terse")
# Walk pages until a predicate matches, then stop
result = await liquid.fetch_until(
adapter, "/orders",
predicate={"customer_email": {"$eq": "vip@co.com"}},
max_pages=20,
)Cross-API normalization
liquid = Liquid(..., normalize_output=True)
# Stripe: {amount: 1000, currency: "usd"}
# PayPal: {value: "10.00", currency_code: "USD"}
# Square: {amount: 1000, currency: "USD"}
# All three normalize to:
Money(amount_cents=1000, currency="USD", amount_decimal=Decimal("10.00"))Unix timestamps, ISO 8601, and RFC 2822 dates all collapse to datetime in UTC. Pagination envelopes ({data: [...]} / {results: [...]} / {items: [...]} / Link headers) flatten to a single PaginationEnvelope. ID fields normalize across id / _id / uid / uuid / *_id conventions.
Intent layer — canonical operations across APIs
# Same intent, any supported API
await liquid.execute_intent("charge_customer", {
"customer_id": "cus_xyz",
"amount_cents": 9999,
"currency": "USD",
})
# Works on Stripe, Braintree, Square, Adyen — one agent mental modelTen canonical intents ship today: charge_customer, refund_charge, create_customer, update_customer, list_orders, cancel_order, send_email, post_message, create_ticket, close_ticket.
Structured recovery — agents self-heal without parsing text
try:
await liquid.fetch(adapter, "/orders")
except LiquidError as e:
if e.recovery and e.recovery.next_action:
# Agent dispatches the action directly — zero text parsing
await agent.call_tool(
e.recovery.next_action.tool,
e.recovery.next_action.args,
)Every Fetcher / Executor error carries a Recovery with next_action: ToolCall, retry_safe: bool, and retry_after_seconds where applicable. 401 → store_credentials. 404/410 → repair_adapter. 429 → retry with retry_after_seconds.
Predictable cost — know before you call
est = await liquid.estimate_fetch(adapter, "/orders")
# FetchEstimate(
# expected_items=250, expected_tokens=52_000, expected_cost_credits=1,
# expected_latency_ms=800, confidence="high", source="empirical"
# )
if est.expected_tokens < my_budget:
data = await liquid.fetch(adapter, "/orders")Every tool emitted by to_tools() also carries a metadata block with cost_credits, typical_latency_ms, cached, cache_ttl_seconds, idempotent, side_effects, expected_result_size, and related_tools so agents can reason about which tool to pick.
Ambient state — no memorization needed
tools = await liquid.to_tools(format="anthropic")
# Auto-includes: liquid_check_quota, liquid_list_adapters, liquid_health_check,
# liquid_check_rate_limit, liquid_get_adapter_info, liquid_estimate_fetch,
# liquid_aggregate, liquid_text_search, liquid_search_nl, liquid_fetch_until,
# liquid_fetch_changes_sinceThe agent asks "how much budget do I have left?" by calling a tool instead of remembering state in its working memory (where it's unreliable).
Response _meta — provenance and truncation signals
liquid = Liquid(..., include_meta=True)
data = await liquid.fetch(adapter, "/orders")
# {
# "data": [...],
# "_meta": {
# "source": "cache", "age_seconds": 180, "fresh": True,
# "truncated": False, "total_count": 523, "next_cursor": "...",
# "adapter": "shopify", "endpoint": "/orders",
# "fetched_at": "2026-04-20T10:00:00Z", "confidence": 0.93
# }
# }Measured impact
Deterministic benchmarks on realistic agent tasks (500-order, 200-ticket fixtures, mocked HTTP) — reproducible via python -m benchmarks.run:
Task | Metric | Baseline | With Liquid | Delta |
Find 10 orders over $100 | tokens | 75,482 | 1,519 | −98% |
Revenue by status (aggregate) | tokens | 75,482 | 115 | −100% |
Fetch customer (id+email only) | tokens | 424 | 12 | −97% |
Recover from 401 | structured next_action | no | yes | — |
Find the shipping ticket | tokens | 14,588 | 154 | −99% |
Stripe↔PayPal consistency | field overlap | 0.11 | 1.00 | +9× |
Skip wasted call via estimate | tokens | 14,943 | 0 | −100% |
| tokens | 14,943 | 1,999 | −87% |
Full methodology + per-task breakdown: benchmarks/RESULTS.md.
Install
pip install liquid-api
pip install 'liquid-api[mcp]' # bundled self-hosted MCP server (liquid-mcp)
pip install 'liquid-api[litellm]' # any of 100+ LLM providers (or [gemini] / [anthropic])
pip install 'liquid-api[grpc]' # gRPC transport (reflection)
pip install 'liquid-api[ws]' # WebSocket transport
# Framework integrations
pip install liquid-langchain # LangChain / LangGraph
pip install liquid-crewai # CrewAISee it work — live, no pre-config
Point Liquid at an API it has never seen (no adapter, no OpenAPI spec, no auth)
and get typed records back. AI is used once for discovery + mapping; every
fetch after is pure HTTP. Runnable end to end —
examples/live_quickstart.py:
liquid = Liquid(llm=my_llm, vault=InMemoryVault(), sink=CollectorSink(),
registry=InMemoryAdapterRegistry())
adapter = await liquid.get_or_create(
url="https://api.openbrewerydb.org/v1/breweries",
target_model={"name": "str", "city": "str", "state": "str", "country": "str"},
auto_approve=True,
)
data = await liquid.fetch(adapter)Real output (Gemini as the LLM backend):
Connecting to an API Liquid has never seen:
https://api.openbrewerydb.org/v1/breweries
discovery method : rest_heuristic
mapped fields : ['name', 'city', 'state', 'country']
LLM calls so far : 2 (discovery + mapping)
fetch() -> 50 typed records; first 3:
{'name': '(405) Brewing Co', 'city': 'Norman', 'state': 'Oklahoma', 'country': 'United States'}
{'name': '(512) Brewing Co', 'city': 'Austin', 'state': 'Texas', 'country': 'United States'}
{'name': '1 of Us Brewing Company', 'city': 'Mount Pleasant', 'state': 'Wisconsin', 'country': 'United States'}
LLM calls during fetch : 0
LLM calls on 2nd fetch : 0Two model calls to learn the API, then zero forever. That's the whole pitch.
Run as an MCP server (open source, self-hosted)
Expose the engine to any MCP client (Claude Desktop, Cursor, Claude Code). It runs the Liquid engine in your own process — no cloud, no account, no lock-in:
pip install 'liquid-api[mcp]'
export OPENAI_API_KEY=sk-... # or GEMINI_API_KEY / ANTHROPIC_API_KEY,
# or OPENAI_BASE_URL=http://localhost:11434/v1 for local (Ollama/vLLM)
liquid-mcp # or: python -m liquid.mcp_serverZero-install with uvx — Claude Code:
claude mcp add liquid --scope user -e OPENAI_API_KEY=sk-... -- uvx --from 'liquid-api[mcp]' liquid-mcpClaude Desktop / any MCP client:
{ "mcpServers": { "liquid": {
"command": "uvx",
"args": ["--from", "liquid-api[mcp]", "liquid-mcp"],
"env": { "OPENAI_API_KEY": "sk-..." }
} } }(Or after pip install 'liquid-api[mcp]', use "command": "liquid-mcp" directly.)
Tools: liquid_connect (discover + map any API), liquid_fetch, liquid_query
(server-side search/aggregate), liquid_estimate (pre-flight cost/size, no HTTP),
liquid_list_adapters, liquid_discover. fetch/query return a _meta block
(service, endpoint, latency, records).
Adapters and credentials persist under ~/.liquid. Backed by any LLM — OpenAI,
Gemini, Anthropic, any OpenAI-compatible/local endpoint via base_url, any of
100+ providers via LiteLLM (LIQUID_LLM_PROVIDER=litellm,
LIQUID_LLM_MODEL=ollama/llama3 / bedrock/... / …), or, in code, your own
function through CallableBackend.
Real run — connecting to an API it had never seen, fully local:
liquid_connect → {"status":"connected","service":"Openbrewerydb","mapped_fields":["name","city","country"]}
liquid_fetch → 50 typed records, e.g. {"name":"(405) Brewing Co","city":"Norman","country":"United States"}Quick start — LangGraph agent with Shopify
from liquid import Liquid, InMemoryCache, RateLimiter
from liquid._defaults import InMemoryVault, InMemoryAdapterRegistry, CollectorSink
from liquid_langchain import LiquidToolkit
from langgraph.prebuilt import create_react_agent
from langchain_openai import ChatOpenAI
liquid = Liquid(
llm=my_llm,
vault=InMemoryVault(),
sink=CollectorSink(),
registry=InMemoryAdapterRegistry(),
cache=InMemoryCache(),
rate_limiter=RateLimiter(),
normalize_output=True, # cross-API canonical shapes
include_meta=True, # _meta block on every response
)
adapter = await liquid.get_or_create(
"https://api.shopify.com",
target_model={"id": "str", "total_cents": "int", "customer_email": "str"},
credentials={"access_token": "shpat_..."},
auto_approve=True,
)
tools = LiquidToolkit(adapter, liquid).get_tools()
agent = create_react_agent(ChatOpenAI(model="gpt-4o-mini"), tools)
result = await agent.ainvoke({
"messages": [("user", "Find 5 recent orders over $100 from VIP customers")],
})The agent's tools come with rich descriptions (WHEN to use, NOT FOR what, return shape, cost), structured recovery on every error, and server-side search so it never pulls 500 orders to find 5.
Framework support
# Anthropic tool use
tools = adapter.to_tools(format="anthropic")
# OpenAI function calling
tools = adapter.to_tools(format="openai")
# MCP (Claude Desktop, Cursor)
tools = adapter.to_tools(format="mcp")
# CrewAI
from liquid_crewai import LiquidCrewToolkit
tools = LiquidCrewToolkit(adapter, liquid).get_tools()
# Opt out of metadata block on tools
tools = adapter.to_tools(format="openai", include_metadata=False)Architecture
URL Agent
↓ ↑
DISCOVERY FETCH / EXECUTE / SEARCH / AGGREGATE
↓ ↑
gRPC · WS · MCP · OpenAPI Deterministic per-protocol transport
GraphQL · SOAP · REST · … • Query DSL (server-side filter)
↓ • Output normalization
APISchema • Verbosity / max_tokens / _meta
↓ • Structured recovery
AI MAPPING (setup only) • Rate-limit-aware token bucket
↓ • Response cache (Cache-Control aware)
AdapterConfig • Empirical probing data (Cloud)AI participates at setup only. Runtime is pure HTTP with transforms — no LLM per call, predictable cost, reproducible behavior. The agent UX layer on top doesn't call an LLM either (except search_nl, which caches compilations).
Discovery pipeline
Method | Where it looks | Cost |
gRPC | server reflection ( | Low |
WebSocket | frame sampling ( | Low |
MCP |
| Low (native protocol) |
OpenAPI |
| Low |
GraphQL |
| Low |
SOAP / WSDL | the WSDL document ( | Low |
REST heuristic | common paths + LLM interpretation | Medium |
Browser | Playwright capturing network | High |
2,500+ APIs are pre-discovered and pre-mapped in the global catalog — most popular services connect with zero discovery cost.
Wire protocols
Liquid speaks more than REST. Discovery tags each endpoint with a protocol, and a
pluggable transport driver runs it — but the agent-facing API (fetch, query,
mapping, recovery, cache, rate limits) is identical across all of them:
Protocol | Runtime | Install |
REST / HTTP+JSON | ✅ built in | — |
GraphQL | ✅ query/mutation + Relay pagination | — |
SOAP / WSDL | ✅ stdlib XML | — |
gRPC | ✅ unary + server-streaming (reflection) |
|
WebSocket | ✅ bounded batch reads + subscribe |
|
New protocols plug in via the liquid.transport.ProtocolDriver protocol.
Protocols
Every component is a swappable Protocol:
from liquid.protocols import (
Vault, LLMBackend, DataSink, KnowledgeStore,
AdapterRegistry, CacheStore,
)In-memory implementations ship for all of them. liquid-cloud provides PostgresVault, RedisCache, etc. for hosted deployments.
Ecosystem
Package | Purpose |
Core library (this repo) | |
LangChain / LangGraph integration | |
CrewAI integration | |
| |
Hosted service + global catalog + empirical probing |
Examples
examples/langchain_agent.py— LangGraph ReAct agentexamples/anthropic_tools.py— Claude tool-use loopexamples/openai_agents.py— OpenAI Assistants
Comparison
Feature | Liquid | Zapier | LangChain tool | DIY |
API discovery | yes | no | no | no |
Server-side search / aggregate | yes | no | no | partial |
Cross-API output normalization | yes | partial | no | no |
Structured recovery with next_action | yes | no | no | no |
Intent layer (canonical operations) | yes | partial | no | no |
Pre-flight cost estimate | yes | no | no | no |
Self-healing on schema drift | yes | no | no | no |
MCP + A2A + LangChain + CrewAI native | yes | no | partial | no |
Open source | yes | no | yes | n/a |
Documentation
Quickstart — discover → map → fetch, plus the no-LLM runtime
OSS vs. Cloud — the honest boundary: what's free/self-hosted vs. hosted
Extending — implement your own Vault / LLM / Sink
Benchmarks — quantitative evidence for each feature
License
AGPL-3.0. Commercial license available for closed-source deployments — contact hello@ertad.com.
Contributing
Community
Maintenance
Latest Blog Posts
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