Best for
- Use when user wants to create a new Freenet dApp, design contract state, implement delegates, build a Freenet-connected UI, OR upgrade an existing dApp — bump freenet-stdlib, ship a new contract/delegate version (v2), f…
freenet/freenet-agent-skills/skills/dapp-builder/SKILL.md
Build and maintain decentralized applications on Freenet using river as a template. Guides through designing contracts (shared state), delegates (private state), and UI, and through upgrading a live dApp safely. Use when user wants to create a new Freenet dApp, design contract state, implement delegates, build a Freenet-connected UI, OR upgrade an existing dApp — bump freenet-stdlib, ship a new contract/delegate version (v2), fix a bug that re-keys the WASM, or migrate state across a contract/de
Decision brief
Build decentralized applications on Freenet following the architecture patterns established in River (decentralized chat).
Compatibility matrix
| Platform | Status | Evidence | What to check |
|---|---|---|---|
| Codex | Not declared | No explicit evidence | Portability before use |
| Claude Code | Not declared | No explicit evidence | Portability before use |
| Cursor | Not declared | No explicit evidence | Portability before use |
| Gemini CLI | Not declared | No explicit evidence | Portability before use |
Installation
The source command is displayed only when detected. A safe inspection prompt is always available so your agent can explain every action before execution.
npx skills add https://github.com/freenet/freenet-agent-skills --skill "skills/dapp-builder"Inspect the Agent Skill "dapp-builder" from https://github.com/freenet/freenet-agent-skills/blob/294f4ad2d7c185f8e7fa4c1ec10802de5673616c/skills/dapp-builder/SKILL.md at commit 294f4ad2d7c185f8e7fa4c1ec10802de5673616c. List every install step, command, network request, credential, file read/write, external action, and rollback step. Explain whether it fits my task. Do not install or execute anything until I approve.
Workflow
Follow these phases in order.
Start by listing each kind of shared state your app needs — each kind becomes its own contract crate. Then design each one in turn using the questions below.
Determine what private data each user needs stored locally and split it across delegates by responsibility (e.g. one delegate per trust boundary or per long-running background task). Most apps need at least one delegate; many need several.
Build the user interface connecting to contracts and delegates. Two approaches:
Set up the build system, CI, and deployment pipeline.
Permission review
The documentation asks the agent to create, modify, or delete local files.
gh issue create --repo freenet/freenet-agent-skills \The documentation asks the agent to run terminal commands or scripts.
git checkout -b improve-<topic>The documentation asks the agent to run terminal commands or scripts.
# Make changes to dapp-builder/SKILL.md or references/*.mdEvidence record
| Signal | Value | Evidence type | Meaning |
|---|---|---|---|
| Quality score | 97/100 | Computed | Documentation, specificity, maintenance, and trust rules |
| Repository stars | 23 | Source | Repository attention, not individual Skill quality |
| Compatibility | 0 platforms | Source | Declared in the catalog source record |
| Usage guide | automated source guide | Editorial | Generated or reviewed according to the visible evidence level |
Pinned source
Build decentralized applications on Freenet following the architecture patterns established in River (decentralized chat).
Freenet is a platform for building decentralized applications that run without centralized servers. Apps store and exchange data through a global, peer-to-peer Key-Value Store shared by every Freenet node.
The keys in that store are not arbitrary strings — they're derived from small pieces of WebAssembly called contracts that define how each value is allowed to change. The next two sections introduce the kinds of components that make up a Freenet app, then explain exactly how contract keys are formed and why that makes the system trustless.
A Freenet app is built from three kinds of components — contracts, delegates, and a UI. Most non-trivial apps have multiple contracts and multiple delegates, each handling a different concern.
A Freenet app typically has one or more contracts, each defining a different kind of shared state. River has a single room contract today, but a more complex app might have several (e.g. rooms, user profiles, invitations, search indexes), and each one is a separate contract crate that compiles to its own WASM.
A Freenet app may have one or more delegates, each handling a different local responsibility — key management, secret storage, background sync, notifications, and so on. Delegates are the local counterpart to contracts: where contracts hold shared state on the network, delegates hold private state on the user's device.
A single UI typically talks to all of an app's contracts and delegates.
"Native app" above means desktop. Freenet does not currently support running a full node on mobile devices. Do not recommend or generate a production mobile wrapper without clearly warning about likely bandwidth, battery, thermal, CPU, and background-execution problems. Treat any such work as experimental, require explicit resource measurements before calling it viable, and do not represent it as an official Freenet client without approval from the Freenet Project.
Now that contracts have been introduced, here's how they're addressed in the network.
The key for a piece of data is derived from the cryptographic hash of the contract's WebAssembly (WASM) code, combined with a set of contract parameters that identify a specific instance.
Freenet solves "Eventual Consistency" using a specific mathematical requirement:
Commutative Monoid: The function that merges updates must be a commutative monoid.
Efficiency: Peers exchange Summaries (compact representations) and Deltas (patches/diffs) rather than re-downloading full state.
Requirement: get_state_delta must not ship state to a peer that already has it. When the requester's summary shows it holds everything you have, the delta carries no information, so it must not contain the state or approach the state's size. It should be a literally empty StateDelta (vec![]), which is the unambiguous "converged" answer and what freenet-scaffold produces for you; a few tens of bytes of encoding framing from serializing an all-empty struct is acceptable. What matters is delta size relative to state size: 20 bytes against a 500 KB state is fine, a state-sized delta is a broken delta mechanism that re-ships everything on every reconciliation, forever. Your summary must likewise be far smaller than your state. Core is adding a probe for contracts that get this wrong, and it currently costs the network real bandwidth. Full detail, code shapes, and a test are in references/contract-patterns.md → "The Delta to an Up-to-Date Peer".
Use deterministic maps in your Summary type: BTreeMap, never HashMap. A HashMap serializes in nondeterministic order (ciborium), so two identical states can summarize to different bytes and core's byte-level convergence check misfires — spurious heals, or missed ones. The same caution applies to any map inside whatever summarize returns.
Beyond that, make sure your state genuinely converges through summarize / delta / apply, and test that it does, rather than assuming a live broadcast reaches every peer.
Previously documented here as a live limitation, now fixed. freenet/freenet-core#4857 ("State updates permanently lost for rarely-changing fields") is CLOSED. A
ContractQueueFulldrop was silent, and the sender cached its own summary as the receiver's on send-Ok, so it believed the peer was current and never re-sent — leaving rarely-changing fields (config, permissions, ban lists) diverged until the ~5-minute InterestSync heartbeat happened to correct them.The shipped fix has the queue-full receiver emit a
ResyncRequest, which makes the sender clear its poisoned summary and re-send full state. It is throttled to one per (contract, peer) per 30s, because #4251 showed that one request per dropped delta amplifies into a full-state storm onto the same saturated queue; #4862 hardened it against bridge backpressure. SeeRESYNC_REQUEST_MIN_INTERVALincrates/core/src/ring/interest.rs.Do not design around multi-minute staleness on rarely-changing fields, and do not treat a ban list or permission field as needing to ride alongside a frequently-changing one. The earlier guidance to do so is retired.
Follow these phases in order.
Already shipped v1 and here to UPGRADE? (bump
freenet-stdlib, ship a new contract/delegate version, or fix a bug that re-keys the WASM) — go straight toreferences/upgrade-and-migration.md→ "Upgrading a Freenet dApp — the painless path", the single start-to-finish playbook. A routine WASM/stdlib bump is low-risk and mechanical when you designed for it at v1, not "recreate everything and all invites die" — River's live 0.6→0.8 stdlib re-key (verified 2026-07-12) auto-migrated every room on refresh, kept every invite and the 78-member Official room intact, and needed no recreation. The phases below build a new dApp; the playbook ties the upgrade steps together (v1 design precondition → reproducible builds → register the outgoing hash →freenet-migrate→ publish → do NOT recreate instances or warn of dead invites).
Start by listing each kind of shared state your app needs — each kind becomes its own contract crate. Then design each one in turn using the questions below.
Key questions (per contract):
identity-and-addressing.md.identity-and-addressing.md → "Cryptographic CAPTCHA". Present the choice to the developer rather than picking silently: ghost keys cost their users money, that money funds Freenet, and the mint is centralized (verification is not). Those are product and architecture decisions, not technical details to settle on the developer's behalf.validate_state/update_state/summarize_state WASM execution cost scales with it too. If a kind of data can grow without bound (message history, uploaded files, a membership list that only grows), don't let one contract instance absorb all of it — shard by the natural unit of write concurrency instead (one contract per room, per user, per time-window, per shard-key, etc.), so each instance stays small regardless of how large the dataset gets in aggregate. See state-authorization-patterns.md → "State Size Budget".Implementation steps:
#[composable] macro from freenet-scaffoldComposableState trait for each componentContractInterface trait for the contractget_state_delta returns a negligible delta (ideally zero bytes, never state-sized) when the requester's summary already matches your state (see contract-patterns.md)upgrade-and-migration.md step 1. Invites and links do not die on an upgrade — River's 0.6→0.8 re-key on the live network kept every room and invite. Recreation is only for deliberately changing the app's identity anchor (e.g. rotating a compromised owner key), never for a routine contract/stdlib bump. The shipped baseline (River #292, Delta) is a backward probe from a committed legacy-code-hash registry: reconstruct each predecessor key from (stable params ‖ old code_hash), GET the old state, fold it forward, and re-PUT under the current key — permissionless because the successor's validate_state re-verifies every byte. The one required operational step is registering the outgoing code hash in the registry before the WASM changes, then republishing. An author-signed OptionalUpgrade pointer is an optional straggler courtesy on top, not the mechanism that moves state. The reusable freenet-migrate crate (0.3.0 on crates.io, with freenet-migrate-build 0.2.0) packages this baseline and owns the probe decisions in a sans-IO driver; it is what River's contract-migration path runs in production (browser UI and riverctl), and existing apps adopt it without a rewrite because its build codegen reads their existing [[entry]] registries and emits view consts matching the hand-rolled shapes (freenet/river#434, #436, #437). See contract-patterns.md → "Contract WASM Upgrade & State Migration". For the cross-cutting operational discipline that keeps the migration itself from losing data (resumable, idempotent, non-destructive, regression-gated, observable), see upgrade-and-migration.md.state-authorization-patterns.md before designing the second iteration. It captures cross-cutting patterns (per-item vs bundled signatures, replay protection via monotonic counter / tombstones / cross-context binding, signed-payload hygiene, time::now() gotchas, related-contracts limits, wire-format stability) that bite on every contract beyond the trivial.References:
references/contract-patterns.md — ContractInterface, commutative monoid, composable state, basic signatures.references/state-authorization-patterns.md — authentication, replay protection, signed-payload hygiene, time, related-contracts, wire-format stability, common pitfalls.references/identity-and-addressing.md — short self-certifying user-facing addresses, keeping large (post-quantum) keys out of identifiers, identity that survives WASM upgrades, and blocking bots without a server (ghost keys vs proof-of-work).Determine what private data each user needs stored locally and split it across delegates by responsibility (e.g. one delegate per trust boundary or per long-running background task). Most apps need at least one delegate; many need several.
Key questions (per delegate):
identity-and-addressing.md → "Cryptographic CAPTCHA" for what it is for, how it pairs with proof-of-work as an escape hatch rather than replacing it, and the two caveats worth relaying to the developer: the mint is centralized, and Freenet has a funding interest in you choosing it.Implementation steps:
DelegateInterface traitExportSecrets handler (an earlier misconception): River's real mechanism messages each old delegate key via DelegateRequest::ApplicationMessages, re-running the old WASM to read its secrets, and folds the signing keys forward (encryption secrets are re-derived). Keep a committed registry of old delegate keys and migrate promptly — the re-run breaks after a stdlib/ABI bump (freenet/river#204). See delegate-patterns.md for the mechanism; freenet-migrate codifies the delegate registry and build codegen, though the delegate secret carry-forward itself still runs app-side today (the crate's field-deployed path is the contract side, freenet-core#2776). See upgrade-and-migration.md for the operational discipline (resumable/interrupted-migration recovery, migration telemetry, and the upgrade test harness).Reference: references/delegate-patterns.md
Build the user interface connecting to contracts and delegates. Two approaches:
Best for: teams already in Rust, complex state logic shared with contracts.
Implementation steps:
<link> / <script> tags from
cdn.jsdelivr.net, cdnjs.cloudflare.com, fonts.googleapis.com, etc.
are blocked in production even though they work in dx serve /
vite dev. See references/ui-patterns.md "Gateway CSP: Vendor Your
Assets".Best for: web developers, faster iteration, familiar tooling (npm, SCSS, etc.).
Implementation steps:
@freenetorg/freenet-stdlib (TypeScript package)FreenetWsApi class for WebSocket connection (handles FlatBuffers serialization)FreenetWsApi constructor (sandbox blocks cookie reading)define to inject contract hashes and delegate key bytes at build timeClientRequestT, ApplicationMessagesT, etc.)A Freenet UI's real render path only runs in a browser. A Dioxus UI ships as a WASM bundle, so rendering a component tree to a string in a Rust test does not exercise the compiled bundle, its event handlers, or its asset paths, and both options reach the node over a WebSocket that unit tests never touch. Drive the UI with Playwright (or equivalent browser automation) from the first screen onward, not only at release time. Treat "I built the component" as unfinished until a browser has loaded it and a script has clicked through it.
dx serve for Dioxus, vite dev for TypeScript) and
drive it with Playwright against mock or offline data, so render correctness,
navigation, and form validation gate every PR. This is the offline tier in
references/production-smoke-testing.md, which has a starter spec.iso tier). Reaching your app there needs
frameLocator and an absolute-URL goto, because the gateway wraps every
webapp in an iframe shell.For interactive debugging rather than scripted specs, the Playwright MCP browser
tools drive a running dx serve or local node directly. See the local-dev
skill, "Debugging with Playwright".
References:
references/ui-patterns.md - WebSocket connection models, gateway CSP,
framework-specific patterns.references/production-smoke-testing.md - the four test tiers, the
development-loop browser-validation recipe, and the iframe-shell Playwright
idioms.Set up the build system, CI, and deployment pipeline.
Implementation steps:
Set up build orchestration — either Makefile.toml (cargo-make) or plain Makefile
Add a preflight task that runs fmt, clippy, tests, and migration checks before publish
Add GitHub Actions CI workflow (runs on push and PRs)
Back up contract state to the delegate for network resilience
Add a production-liveness smoke test. A ~50-line Playwright spec
asserting the gateway-hosted webapp mounts, vendored CSS loaded, and the
browser console is clean catches CSP blocks, iframe-shell mistakes, and
broken archives that no unit test reaches. See
references/production-smoke-testing.md.
Check the gateway port and (optionally) tar reproducibility. The
gateway runs on 7509 — older docs and scripts still reference 50509.
For byte-reproducible webapp archives across build hosts, invoke tar
with the GNU flags listed under "Tooling Preflight" in
references/build-system.md.
If you'll ship more than one release, plan for a facade contract
from day one. Without it, every release rotates the gateway URL
users have bookmarked. The facade is a stable-URL indirection: a
never-rebuilt contract whose state holds a signed pointer to the
current web-container. See references/facade-pattern.md. Cheaper
to design in now than retrofit later — retrofitting means asking
every existing user to update their bookmark.
Plan contract-WASM stability before the first release. A
cargo update in the workspace root must not silently rotate
contract IDs. See references/build-system.md →
"Per-contract lockfile isolation".
Test the upgrade path and make migration resumable. The dangerous
inputs are old-state -> new-code and interrupted migration, neither
exercised by testing the new version on fresh state. Add an old-format-load
test and an interrupted-migration-recovery test, and make migration
idempotent + resumable (in-progress marker cleared only on full success) +
non-destructive + regression-gated + observable. See
references/upgrade-and-migration.md.
References:
references/build-system.md — build, CI, packaging, tooling
preflight, per-contract lockfile isolation, contract-ID
reproducibility caveat, pre-commit hook for stray .wasm.references/production-smoke-testing.md — iframe shell architecture,
Playwright recipe for post-publish liveness checks.references/facade-pattern.md — stable-URL facade contract
architecture for projects that ship more than one release.references/upgrade-and-migration.md — operational discipline for safe
contract/delegate upgrades: the five migration properties (idempotent,
resumable, non-destructive, regression-gated, observable), enumerating
dynamic key families, the upgrade test harness, and staged reversible rollout.my-dapp/
├── common/ # Shared types between contract/delegate/UI
│ └── src/
│ ├── lib.rs
│ └── state/ # State definitions
├── contracts/ # one subdirectory per contract crate
│ ├── room-contract/
│ │ ├── Cargo.toml
│ │ └── src/lib.rs # ContractInterface implementation
│ └── profile-contract/ # add more as the app grows
│ └── ...
├── delegates/ # one subdirectory per delegate crate
│ ├── chat-delegate/
│ │ ├── Cargo.toml
│ │ └── src/lib.rs # DelegateInterface implementation
│ └── identity-delegate/ # add more as the app grows
│ └── ...
├── ui/
│ ├── Cargo.toml
│ ├── Dioxus.toml
│ └── src/
│ ├── main.rs
│ └── components/
├── Cargo.toml # Workspace root
└── Makefile.toml # cargo-make build tasks
my-dapp/
├── contracts/
│ └── my-contract/
│ ├── Cargo.toml
│ └── src/lib.rs # ContractInterface implementation
├── delegates/
│ └── my-delegate/
│ ├── Cargo.toml
│ └── src/lib.rs # DelegateInterface implementation
├── web/
│ ├── package.json
│ ├── vite.config.ts # Injects contract/delegate keys at build time
│ ├── tsconfig.json
│ ├── index.html
│ └── src/
│ ├── index.ts # Entry point, connection flow
│ ├── freenet-api.ts # FreenetWsApi wrapper
│ ├── delegate-api.ts # Delegate FlatBuffers message building
│ ├── identity.ts # Identity management (delegate + fallback)
│ ├── types.ts # Shared TypeScript types
│ └── components/ # UI components
├── Cargo.toml # Workspace root (contracts + delegates)
└── Makefile # Build orchestration
River demonstrates all patterns:
contracts/room-contract/delegates/chat-delegate/ui/common/Track the versions River (the reference dApp) uses. Mismatched versions cause deserialization failures, missing features, and "variant index out of range" errors. Check River's workspace Cargo.toml before pinning.
As of May 2026 — River pins freenet-stdlib = "0.6.0" but the upstream
crate is now 0.8 (0.6 → 0.7 added Base58-stringified contract_states
keys in NodeDiagnosticsResponse; 0.7 → 0.8 hardened wire-boundary enums
with #[non_exhaustive] and removed the world-known DEFAULT_CIPHER /
DEFAULT_NONCE constants). If you build only against River, mirror its
pin; if your code links into stdlib 0.8 directly, you need the bumped
version and the wildcard match arms / random cipher generation
documented in references/delegate-patterns.md.
# Workspace-wide (Cargo.toml) — track this against stdlib 0.8 once River bumps.
freenet-stdlib = { version = "0.8", features = ["contract"] }
freenet-scaffold = "0.2.2"
freenet-scaffold-macro = "0.2.2"
# UI crate (ui/Cargo.toml): enables WebApi/WebSocket helpers
freenet-stdlib = { workspace = true, features = ["net"] }
# UI framework
dioxus = { version = "0.7.3", features = ["web"] }
The contract feature is required for contract crates targeting
wasm32-unknown-unknown; use the delegate feature for delegate crates.
The net feature pulls in WebApi for the UI.
For UIs built with TypeScript + Vite (Option B in Phase 3), depend on the
matching @freenetorg/freenet-stdlib release:
{
"dependencies": {
"@freenetorg/freenet-stdlib": "^0.2.0"
},
"devDependencies": {
"vite": "^6.0",
"typescript": "^5.0",
"sass": "^1.0"
}
}
The TS package v0.2.0 brought the API to parity with the Rust client:
FreenetWsApi with promise-based get/put/update/subscribe/
disconnect (await api.X(...)), full ResponseHandler including
onContractNotFound/onSubscribeResponse/onClose, inbound
ReassemblyBuffer, and transparent outbound chunking for payloads
512 KB. Callbacks still fire alongside promises for backward compatibility; the default request timeout is 30 s. See
references/ui-patterns.mdfor the full pattern and a warning about the privatesendRequestcast used for delegate messages until a public builder lands.
stdlib v0.6.0 (PR #75) removed the public constants DEFAULT_CIPHER
and DEFAULT_NONCE to close a CVE-class issue (world-known keys leaked
into any binary that imported them). Delegates that previously used these
must now generate random values per session — e.g.
let key: [u8; 32] = rand::random(); let nonce: [u8; 24] = rand::random();.
Code still referencing the old constants will fail to compile against
stdlib 0.6 or newer.
This skill is designed to be self-improving. When encountering issues while using this skill, agents should file GitHub issues or submit PRs to improve it.
File an issue at freenet/freenet-agent-skills when:
gh issue create --repo freenet/freenet-agent-skills \
--title "dapp-builder: <brief description>" \
--body "## Problem
<describe what was unclear or incorrect>
## Context
<what were you trying to accomplish>
## Suggested Improvement
<optional: how the skill could be improved>"
For concrete improvements:
# Clone and create branch
gh repo clone freenet/freenet-agent-skills
cd freenet-agent-skills
git checkout -b improve-<topic>
# Make changes to dapp-builder/SKILL.md or references/*.md
# ... edit files ...
# Submit PR
git add -A && git commit -m "dapp-builder: <description>"
gh pr create --title "dapp-builder: <description>" \
--body "## Changes
<describe improvements>
## Reason
<why this helps>"
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