Show HN: Forge – Guardrails take an 8B model from 53% to 99% on agentic tasks
338 points - yesterday at 12:23 PM
Hi HN, I'm Antoine Zambelli, AI Director at Texas Instruments.
I built Forge, an open-source reliability layer for self-hosted LLM tool-calling.
What it does:
- Adds domain-and-tool-agnostic guardrails (retry nudges, step enforcement, error recovery, VRAM-aware context management) to local models running on consumer hardware
- Takes an 8B model from ~53% to ~99% on multi-step agentic workflows without changing the model - just the system around it
- Ships with an eval harness and interactive dashboard so you can reproduce every number
I wanted to run a handful of always-on agentic systems for my portfolio, didn't want to pay cloud frontier costs, and immediately hit the compounding math problem on local models. 90% per-step accuracy sounds great, but with a 5-step workflow that's a 40% failure rate. No existing framework seemed to address this mechanical reliability issue - they all seemed tailor-made for cloud frontier.
Demo video: https://youtu.be/MzRgJoJAXGc (side-by-side: same model, same task, with and without Forge guardrails)
The paper (accepted to ACM CAIS '26, presenting May 26-29 in San Jose) covers the peer-reviewed findings across 97 model/backend configurations, 18 scenarios, 50 runs each. Key numbers:
- Ministral 8B with Forge: 99.3%. Claude Sonnet with Forge: 100%. The gap between a free local 8B model on a $600 GPU and a frontier API is less than 1 point.
- The same 8B local model with Forge (99.3%) outperforms Claude Sonnet without guardrails (87.2%) - an 8B model with framework support beats the best result you can get through frontier API alone.
- Error recovery scores 0% for every model tested - local and frontier - without the retry mechanism. Not a capability gap, an architectural absence.
I'm currently using this for my home assistant running on Ministral 14B-Reasoning, and for my locally hosted agentic coding harness (8B managed to contribute to the codebase!).
The guardrail stack has five layers, each independently toggleable. The two that carry the most weight (per ablation study with McNemar's test): retry nudges (24-49 point drops when disabled) and error recovery (~10 point drops, significant for every model tested). Step enforcement is situational - only fires for models with weaker sequencing discipline. Rescue parsing and context compaction showed no significance in the eval but are retained for production workloads where they activate once in a while.
One thing I really didn't expect: the serving backend matters. Same Mistral-Nemo 12B weights produce 7% accuracy on llama-server with native function calling and 83% on Llamafile in prompt mode. A 75-point swing from infrastructure alone. I don't think anyone's published this because standard benchmarks don't control for serving backend.
Another surprise: there's no distinction in current LLM tool-calling between "the tool ran successfully and returned data" and "the tool ran successfully but found nothing." Both return a value, the orchestrator marks the step complete, and bad data cascades downstream. It's the equivalent of HTTP having 200 but no 404. Forge adds this as a new exception class (ToolResolutionError) - the model sees the error and can retry instead of silently passing garbage forward.
Biggest technical challenge was context compaction for memory-constrained hardware. Both Ollama and Llamafile silently fall back to CPU when the model exceeds VRAM - no warning, no error, just 10-100x slower inference. Forge queries nvidia-smi at startup and derives a token budget to prevent this.
How to try it:
- Clone the repo, run the eval harness on a model I haven't tested. If you get interesting results I'll add them to the dashboard.
- Try the proxy server mode - point any OpenAI-compatible client at Forge and it handles guardrails transparently. It's the newest model and I'd love more eyes on it.
- Dogfooding led me to optimize model parameters in v0.6.0. The harder eval suite (26 scenarios) is designed to raise the ceiling so no one sits at 100%. Several that did on the original suite can't sweep it - including Opus 4.6. Curious if anyone finds scenarios that expose gaps I haven't thought of. Paper numbers based on pre v0.6.0 code.
Background: prior ML publication in unsupervised learning (83 citations). This paper accepted to ACM CAIS '26 - presenting May 26-29.
Repo: https://github.com/antoinezambelli/forge
Paper: https://www.caisconf.org/program/2026/demos/forge-agentic-re... https://github.com/antoinezambelli/forge/blob/main/docs/forg...
Dashboard: https://github.com/antoinezambelli/forge/docs/results/dashbo...
Comments
- Breaking down a problem into a planned execution, with executing agent providing the initial plan which includes explicit objectives such as which tools it calls and what it would consider to be a successful execution.
- The harness then executes the plan in order
- Each step that involves a tool call will be executed by breaking down the tool call into component parts: the harness interrogates the agent for a valid parameter value for the current tool argument. The tool definition contains validators for each argument. If the validator fails, the harness rewinds the conversation and injects the failure reason into the next try.
- Once the agent produces a valid response for the argument, the harness proceeds to the next argument.
- Once all the arguments have been filled, the harness calls the tool. It passes the agent's initial expected value along with the actual value, along with any errors that may have been produced and asks the agent if it is satisfied with the result. If it isn't, the agent provides a reason and the harness then retries the tool call process from the beginning rewinding the conversation and inserting the reasoning for the retry.
- The agent may request to re-plan if it discovers a flaw in its initial plan. The harness will also attempt to re-plan if the agent produces too many failures in a row.
This proves to be quite effective at reducing tool call failures. One benefit is that the sub-agent gets a perfect conversation history where it makes no mistakes. I'm not sure if it's actually better at completing tasks though, I haven't tried to benchmark it.
The retry-nudge layer maps almost 1:1 to what I do manually multiple times an hour: "no, that wasn't a tool failure, the file just doesn't contain that pattern, try X." Encoding it at the framework level is the right shape.
Have you looked at whether these guardrails close the smaller frontier-model gap on long-horizon tasks? My intuition is the 87→99 delta on Sonnet won't quite hold past ~50 steps, where context drift starts dominating more than retry semantics.
I thought Llamafile was just a model and llama.cpp bundled in to a single binary - is this the difference between Llamafile injecting a default sysmtem prompt vs hitting the raw llama-server endpoint with no harness?
That seems like comparing apples to apple pie, there's some ingredients missing.
This was part of testing out how well a tool of mine worked (github.com/jsuppe/loom), which aims to be used to extracts requirements, specs, creates tests. At first I had no intention of using it for code generation but then tried it out with some early success. I tried splitting the work by using the tool with different frontier models, and then providing work to a local ollama instance running one of several models. Not all local models had the same outcome, not all coding languages had the same outcome. I also found in this experiment, when nailing down the coding tasks I wanted to set up positive and negative scenarios- which is where I found setting guardrails can sometimes backfire with inversion- this essentially elaborates on previous work by Khan 2025 (https://arxiv.org/abs/2510.22251); the most interesting finding to me was that if you give guardrails with a rationale, it reduces compliance and may cause the inversion
For coding tasks I found that the improvement was not only ability to use a lower cost model for these broken down tasks, but wall clock time was improved over using frontier model alone, with equivalent outcomes.
One of the most surprising findings was when a 9B model self-corrected through 4 tool parse failures within the guard rails. It tried to use a complex tool (patch_file), kept failing and eventually downshifted to a simpler tool (edit_line) that it could actually execute. The guardrails didn't make the model smarter, it just narrowed the execution space until it could find something that worked.
Basically this is a tool auto-complete that has a workflow element to it with certain steps that need to happen in certain order. In other words the order is defined in advance. Am I correct?
Basically execute step 1 first, then step 2 and finally step 3 and this is the schema for each step. That is effectively the guardrail and there is retry logic.
If it is the case, this is obviously useful but in a very specific set of problems where the solution is kind of known in advance. A workflow automation might work but this is kind of N8N where each step is LLM step.
Anyway, I might me wrong but I wanted to share a few thoughts.
I've been exploring this area and a project like https://github.com/itayinbarr/little-coder (not my work) lets me mix and match with my current setup or any plugins built for pi.
Very early prototype, so I’m looking more for architectural/conceptual reactions than polish: https://wardwright.dev / https://github.com/bglusman/wardwright
The common thread I see is treating the harness around the model as first-class infrastructure. Forge seems focused on tool-call correctness and recovery; Wardwright is more about controlling what the agent is supposed to do, where work gets routed, and how the operator stays in the loop.
Curious whether you see those as complementary layers. I’m planning to try Forge and would be interested in seeing whether they fit together cleanly.
> python -m forge.proxy --backend-url http://localhost:8080 --port 8081
This is a good example because I've currently stuck with llama.cpp's UI. I can read your code (or throw Gemma at it =p ) but thought I'd ask anyway.
In this example, what is it exactly that your proxy is fortifying? The HTTP SSE requests? (Those would be `/chat/completions`.)
Interested in using this for Home Assistant using a Mac Mini as my server. Does it run on MacOS?
How is the latency when using the proxy? I’m using Claude Haiku 4.5 for my voice assistant right now and it’s pretty fast, but if I could keep the LLM local, it’d be even better.
I'll be keen to look through the code on this!
... which lead me to realize that it's one of those terms with multiple meanings - like "agent" or even "AI" itself - but where people who use it may not be aware of how many different definitions are floating around.
In this project it refers to validating tool calls - fixing invalid tool responses, making sure certain required tool calls have been made, maintaining an error budget after which the task is abandoned with an error.
Other projects might use "guardrails" to mean protecting against unsafe content (Llama Gaurd), refusing off-topic queries (NVIDIA NeMo Guardrails "topical rails", filtering PII, detecting jailbreaks, or human-in-the-loop checks of specific actions.
I've even seen people talk about running a coding agent in a sandbox (Docker, Firecracker etc) as a form of guardrail.
Interesting point about backend variance. Do you think serving layer should become part of standard LLM eval reporting?
The https://swival.dev harness already has retry nudges, step enforcement, error recovery, context awareness, etc. to try to support small models as much as possible.
Curious to see how it compares with forge, and if both could be combined.