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Deep agents expose a filesystem surface to the agent via tools like ls, read_file, write_file, edit_file, glob, and grep. These tools operate through a pluggable backend. This page explains how to choose a backend, route different paths to different backends, implement your own virtual filesystem (e.g., S3 or Postgres), add policy hooks, and comply with the backend protocol.

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Quickstart

Here are a few pre-built filesystem backends that you can quickly use with your deep agent:
Built-in backendDescription
Defaultagent = create_deep_agent()
Ephemeral in state. The default filesystem backend for an agent is stored in langgraph state. Note that this filesystem only persists for a single thread.
Local filesystem persistenceagent = create_deep_agent(backend=FilesystemBackend(root_dir="/Users/nh/Desktop/"))
This gives the deep agent access to your local machine’s filesystem. You can specify the root directory that the agent has access to. Note that any provided root_dir must be an absolute path.
Durable store (LangGraph store)agent = create_deep_agent(backend=lambda rt: StoreBackend(rt))
This gives the agent access to long-term storage that is persisted across threads. This is great for storing longer term memories or instructions that are applicable to the agent over multiple executions.
CompositeEphemeral by default, /memories/ persisted. The Composite backend is maximally flexible. You can specify different routes in the filesystem to point towards different backends. See Composite routing below for a ready-to-paste example.

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Built-in backends

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StateBackend (ephemeral)

# By default we provide a StateBackend
agent = create_deep_agent()

# Under the hood, it looks like
from deepagents.backends import StateBackend

agent = create_deep_agent(
    backend=(lambda rt: StateBackend(rt))   # Note that the tools access State through the runtime.state
)
How it works:
  • Stores files in LangGraph agent state for the current thread.
  • Persists across multiple agent turns on the same thread via checkpoints.
Best for:
  • A scratch pad for the agent to write intermediate results.
  • Automatic eviction of large tool outputs which the agent can then read back in piece by piece.
Note that this backend is shared between the supervisor agent and subagents, and any files a subagent writes will remain in the LangGraph agent state even after that subagent’s execution is complete. Those files will continue to be available to the supervisor agent and other subagents.

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FilesystemBackend (local disk)

from deepagents.backends import FilesystemBackend

agent = create_deep_agent(
    backend=FilesystemBackend(root_dir=".", virtual_mode=True)
)
How it works:
  • Reads/writes real files under a configurable root_dir.
  • You can optionally set virtual_mode=True to sandbox and normalize paths under root_dir.
  • Uses secure path resolution, prevents unsafe symlink traversal when possible, can use ripgrep for fast grep.
Best for:
  • Local projects on your machine
  • CI sandboxes
  • Mounted persistent volumes

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StoreBackend (LangGraph store)

from langgraph.store.memory import InMemoryStore
from deepagents.backends import StoreBackend

agent = create_deep_agent(
    backend=(lambda rt: StoreBackend(rt)),   # Note that the tools access Store through the runtime.store
    store=InMemoryStore()
)
How it works:
  • Stores files in a LangGraph BaseStore provided by the runtime, enabling cross‑thread durable storage.
Best for:
  • When you already run with a configured LangGraph store (for example, Redis, Postgres, or cloud implementations behind BaseStore).
  • When you’re deploying your agent through LangSmith Deployment (a store is automatically provisioned for your agent).

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CompositeBackend (router)

from deepagents import create_deep_agent
from deepagents.backends import CompositeBackend, StateBackend, StoreBackend
from langgraph.store.memory import InMemoryStore

composite_backend = lambda rt: CompositeBackend(
    default=StateBackend(rt),
    routes={
        "/memories/": StoreBackend(rt),
    }
)

agent = create_deep_agent(
    backend=composite_backend,
    store=InMemoryStore()  # Store passed to create_deep_agent, not backend
)
How it works:
  • Routes file operations to different backends based on path prefix.
  • Preserves the original path prefixes in listings and search results.
Best for:
  • When you want to give your agent both ephemeral and cross-thread storage, a CompositeBackend allows you provide both a StateBackend and StoreBackend
  • When you have multiple sources of information that you want to provide to your agent as part of a single filesystem.
    • e.g. You have long-term memories stored under /memories/ in one Store and you also have a custom backend that has documentation accessible at /docs/.

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Specify a backend

  • Pass a backend to create_deep_agent(backend=...). The filesystem middleware uses it for all tooling.
  • You can pass either:
    • An instance implementing BackendProtocol (for example, FilesystemBackend(root_dir=".")), or
    • A factory BackendFactory = Callable[[ToolRuntime], BackendProtocol] (for backends that need runtime like StateBackend or StoreBackend).
  • If omitted, the default is lambda rt: StateBackend(rt).

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Route to different backends

Route parts of the namespace to different backends. Commonly used to persist /memories/* and keep everything else ephemeral. 
from deepagents import create_deep_agent
from deepagents.backends import CompositeBackend, StateBackend, FilesystemBackend

composite_backend = lambda rt: CompositeBackend(
    default=StateBackend(rt),
    routes={
        "/memories/": FilesystemBackend(root_dir="/deepagents/myagent", virtual_mode=True),
    },
)

agent = create_deep_agent(backend=composite_backend)
Behavior:
  • /workspace/plan.md → StateBackend (ephemeral)
  • /memories/agent.md → FilesystemBackend under /deepagents/myagent
  • ls, glob, grep aggregate results and show original path prefixes.
Notes:
  • Longer prefixes win (for example, route "/memories/projects/" can override "/memories/").
  • For StoreBackend routing, ensure the agent runtime provides a store (runtime.store).

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Use a virtual filesystem

Build a custom backend to project a remote or database filesystem (e.g., S3 or Postgres) into the tools namespace. Design guidelines:
  • Paths are absolute (/x/y.txt). Decide how to map them to your storage keys/rows.
  • Implement ls_info and glob_info efficiently (server-side listing where available, otherwise local filter).
  • Return user-readable error strings for missing files or invalid regex patterns.
  • For external persistence, set files_update=None in results; only in-state backends should return a files_update dict.
S3-style outline: 
from deepagents.backends.protocol import BackendProtocol, WriteResult, EditResult
from deepagents.backends.utils import FileInfo, GrepMatch

class S3Backend(BackendProtocol):
    def __init__(self, bucket: str, prefix: str = ""):
        self.bucket = bucket
        self.prefix = prefix.rstrip("/")

    def _key(self, path: str) -> str:
        return f"{self.prefix}{path}"

    def ls_info(self, path: str) -> list[FileInfo]:
        # List objects under _key(path); build FileInfo entries (path, size, modified_at)
        ...

    def read(self, file_path: str, offset: int = 0, limit: int = 2000) -> str:
        # Fetch object; return numbered content or an error string
        ...

    def grep_raw(self, pattern: str, path: str | None = None, glob: str | None = None) -> list[GrepMatch] | str:
        # Optionally filter server‑side; else list and scan content
        ...

    def glob_info(self, pattern: str, path: str = "/") -> list[FileInfo]:
        # Apply glob relative to path across keys
        ...

    def write(self, file_path: str, content: str) -> WriteResult:
        # Enforce create‑only semantics; return WriteResult(path=file_path, files_update=None)
        ...

    def edit(self, file_path: str, old_string: str, new_string: str, replace_all: bool = False) -> EditResult:
        # Read → replace (respect uniqueness vs replace_all) → write → return occurrences
        ...
Postgres-style outline:
  • Table files(path text primary key, content text, created_at timestamptz, modified_at timestamptz)
  • Map tool operations onto SQL:
    • ls_info uses WHERE path LIKE $1 || '%'
    • glob_info filter in SQL or fetch then apply glob in Python
    • grep_raw can fetch candidate rows by extension or last modified time, then scan lines

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Add policy hooks

Enforce enterprise rules by subclassing or wrapping a backend. Block writes/edits under selected prefixes (subclass): 
from deepagents.backends.filesystem import FilesystemBackend
from deepagents.backends.protocol import WriteResult, EditResult

class GuardedBackend(FilesystemBackend):
    def __init__(self, *, deny_prefixes: list[str], **kwargs):
        super().__init__(**kwargs)
        self.deny_prefixes = [p if p.endswith("/") else p + "/" for p in deny_prefixes]

    def write(self, file_path: str, content: str) -> WriteResult:
        if any(file_path.startswith(p) for p in self.deny_prefixes):
            return WriteResult(error=f"Writes are not allowed under {file_path}")
        return super().write(file_path, content)

    def edit(self, file_path: str, old_string: str, new_string: str, replace_all: bool = False) -> EditResult:
        if any(file_path.startswith(p) for p in self.deny_prefixes):
            return EditResult(error=f"Edits are not allowed under {file_path}")
        return super().edit(file_path, old_string, new_string, replace_all)
Generic wrapper (works with any backend): 
from deepagents.backends.protocol import BackendProtocol, WriteResult, EditResult
from deepagents.backends.utils import FileInfo, GrepMatch

class PolicyWrapper(BackendProtocol):
    def __init__(self, inner: BackendProtocol, deny_prefixes: list[str] | None = None):
        self.inner = inner
        self.deny_prefixes = [p if p.endswith("/") else p + "/" for p in (deny_prefixes or [])]

    def _deny(self, path: str) -> bool:
        return any(path.startswith(p) for p in self.deny_prefixes)

    def ls_info(self, path: str) -> list[FileInfo]:
        return self.inner.ls_info(path)
    def read(self, file_path: str, offset: int = 0, limit: int = 2000) -> str:
        return self.inner.read(file_path, offset=offset, limit=limit)
    def grep_raw(self, pattern: str, path: str | None = None, glob: str | None = None) -> list[GrepMatch] | str:
        return self.inner.grep_raw(pattern, path, glob)
    def glob_info(self, pattern: str, path: str = "/") -> list[FileInfo]:
        return self.inner.glob_info(pattern, path)
    def write(self, file_path: str, content: str) -> WriteResult:
        if self._deny(file_path):
            return WriteResult(error=f"Writes are not allowed under {file_path}")
        return self.inner.write(file_path, content)
    def edit(self, file_path: str, old_string: str, new_string: str, replace_all: bool = False) -> EditResult:
        if self._deny(file_path):
            return EditResult(error=f"Edits are not allowed under {file_path}")
        return self.inner.edit(file_path, old_string, new_string, replace_all)

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Protocol reference

Backends must implement the BackendProtocol. Required endpoints:
  • ls_info(path: str) -> list[FileInfo]
    • Return entries with at least path. Include is_dir, size, modified_at when available. Sort by path for deterministic output.
  • read(file_path: str, offset: int = 0, limit: int = 2000) -> str
    • Return numbered content. On missing file, return "Error: File '/x' not found".
  • grep_raw(pattern: str, path: Optional[str] = None, glob: Optional[str] = None) -> list[GrepMatch] | str
    • Return structured matches. For an invalid regex, return a string like "Invalid regex pattern: ..." (do not raise).
  • glob_info(pattern: str, path: str = "/") -> list[FileInfo]
    • Return matched files as FileInfo entries (empty list if none).
  • write(file_path: str, content: str) -> WriteResult
    • Create-only. On conflict, return WriteResult(error=...). On success, set path and for state backends set files_update={...}; external backends should use files_update=None.
  • edit(file_path: str, old_string: str, new_string: str, replace_all: bool = False) -> EditResult
    • Enforce uniqueness of old_string unless replace_all=True. If not found, return error. Include occurrences on success.
Supporting types:
  • WriteResult(error, path, files_update)
  • EditResult(error, path, files_update, occurrences)
  • FileInfo with fields: path (required), optionally is_dir, size, modified_at.
  • GrepMatch with fields: path, line, text.
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