Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx skills add ariaramin/flutter-skills --skill dart-flutter-ffi-systems-engineeringgit clone --depth 1 https://github.com/ariaramin/flutter-skillsWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/ariaramin/flutter-skills/dart-flutter-ffi-systems-engineering)<a href="https://agentmods.dev/skills/ariaramin/flutter-skills/dart-flutter-ffi-systems-engineering"><img src="https://agentmods.dev/badge/skills/ariaramin/flutter-skills/dart-flutter-ffi-systems-engineering/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/ariaramin/flutter-skills/dart-flutter-ffi-systems-engineering"><img src="https://agentmods.dev/badge/skills/ariaramin/flutter-skills/dart-flutter-ffi-systems-engineering.svg" alt="Reviewed on agentmods" width="80" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00136 | $0.04987 |
| Opus 5.5 | $0.00054 | $0.01995 |
| Sonnet 5.5 | $0.00027 | $0.00997 |
| Haiku 4.5 | $0.00014 | $0.00499 |
Grade A, and why
dart-flutter-ffi-systems-engineering scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 7d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 487 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Dart & Flutter FFI Systems Engineering
Treat FFI as a systems boundary, not ordinary Dart API usage. Compilation, symbol resolution, or one successful call does not prove correctness. Every native boundary must make these contracts explicit:
ABI
ownership
lifetime
threading
error model
packaging
performance
Prefer this architecture:
application/domain
↓
safe Dart wrapper
↓
generated/raw FFI bindings
↓
small stable C ABI
↓
native implementation
Keep raw pointers, allocators, native structs, function pointers, and DynamicLibrary out of UI/domain code.
Reference routing
Read only what the task needs:
| Need | Reference |
|---|---|
FFI vs Dart/plugins, toolchain gates, exact type mapping, ffigen, @Native, dynamic loading, build hooks |
references/01-decisions-toolchain-bindings.md |
| Memory ownership, allocators, finalizers, pointers, structs/unions, strings, callbacks | references/02-memory-layout-strings-callbacks.md |
Isolates/threading, errors, errno, native crashes, varargs, globals, function pointers, ABI versioning |
references/03-concurrency-errors-api-versioning.md |
| Android/iOS/macOS/Windows/Linux/Web packaging, architecture support, performance, profiling, sanitizers, symbols, supply chain/security | references/04-platform-build-performance-security.md |
| Ownership matrices, checklists, audit, testing, fuzzing, migration, anti-patterns, workflow, evidence/source rules | references/05-ownership-matrices-audit-testing-migration.md |
1. Decide whether FFI is justified
Before adding native code, answer:
- What capability or measured performance need requires native code?
- Could pure Dart solve it adequately?
- Could an existing Flutter plugin/platform channel solve it more safely?
- Is the native API C-compatible, or can you expose a stable C shim?
- Is Web required?
- Can every required OS/architecture build and package the library?
- Will marshaling/copy/allocation dominate the native computation?
- Who will maintain native toolchains, symbols, security updates, and ABI compatibility? Use FFI for C-compatible native libraries, compute-heavy kernels, codecs, cryptography, databases, scientific/numerical code, compression, parsers, or reusable native algorithms when the value justifies the systems cost. Avoid FFI for trivial Dart logic, rich platform-UI lifecycle APIs, or workloads where conversion/copy costs erase the benefit. Do not say “FFI is faster.” State the mechanism: it removes platform-message serialization and makes a direct ABI call; end-to-end speed still depends on conversions, allocations, copies, synchronization, and native work.
What ships with it
5 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 7d ago First seen · 487 lines · 136 tokens per session scan A df42a720f65b
dart-flutter-ffi-systems-engineering is a skill published in the GitHub repository ariaramin/flutter-skills (6 stars, last pushed 7d ago), licensed MIT. It adds 136 tokens to every session and 4,987 once invoked, about $0.0005 per session on Opus 5.5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-10-11.
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