He told the Scottish Parliament's education committee: "We're not regulators or meter-readers ticking boxes."
Mr Osler said the 5-14 programme was designed to reflect best practice. It would be "entirely open" to education authorities to vary it if they thought that was no longer the case.
But Nicola Sturgeon, the SNP's education spokesperson, suggested that was "a highly theoretical statement". Most schools and authorities saw the guidelines as all but compulsory, she said.
Mr Osler agreed this was a "wide perception," but said some authorities had already begun to depart from the guidelines. He added that, given these were issued as national advice, it was "entirely reasonable" for the inspectorate to draw attention to any departure from them. But the central concern of HMI was simply to evaluate the quality of the experience of individual pupils.
Mr Osler also rebutted the broadside against the inspectorate issued by the Educational Institute of Scotland before Christmas. Ronnie Smith, the union's general secretary, accused HMI of operating a "climate of fear." Mr Osler described his remarks as "disappointing behaviour".
The inspectorate had no evidence such complaints are well-founded, Mr Osler said. The EIS was virtually suggesting that the inspectorate "should get involved in a professional conspiracy to highlight strngths and conceal weaknesses".
Mr Osler revealed that he had commissioned an independent System 3 poll covering parents, teachers and pupils in 90 primary and secondary schools that had been recently inspected. This did not provide any evidence to back the EIS claims, although it had come up with "helpful advice."
He told The TESS later that people's views changed dramatically from the beginning of an inspection to the end, when the process was found to be valuable. Teachers did feel, however, that they should receive more feedback about their teaching and HMI was considering that.
The Parliamentary committee, which was beginning a series of hearings into the Education Bill, also heard pleas from the General Teaching Council for Scotland that the proposed extension of its powers to strike off incompetent teachers and promote continuous professional development should be strengthened.
Ivor Sutherland, the registrar, said the compromise in the bill where the education authority would dismiss incompetent teachers followed by possible GTC deregistration would not work if the authorities did nothing. "Their track record has not been particularly good," he said.
There was evidence of cross-party support in the committee for parents, teachers and others to be able to refer cases of incompetence directly to the GTC.
Gordon Kirk, the GTC's vice-convener, said the council should also be able to approve courses of continuous professional development. Teachers should not feel they could enter the profession "with two Highers and a vaccination".